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Electrochemical disinfection via in-situ H 2 O 2 generation through two-electron oxygen reduction (2e--ORR) is deemed as an alternative to traditional chemical dosing disinfection methods. However, its disinfection performance is still confined by its low H 2 O 2 yield, which largely relies on the electronic structure of cathode along with O 2 mass transport, especially for immersed cathode. To tackle this concern, we developed a pulsed-assisted MXene-based electrochemical system with both electronic effect and mass transport being taken into consideration. MXene-based cathode (F-Ti 3 C 2 MXene/CF) was designed by electrodeposition monolayer Ti 3 C 2 T x MXene onto different substrates, which endowed surface groups good for 2e--ORR. Firstly, electrodeposition parameters were investigated including electrodeposition voltage, time and two porous substrates (carbon-based carbon fiber and metal-base nickel foam). Then, H 2 O 2 production was evaluated by pulsed-assisted MXene-based electrochemical configuration, where H 2 O 2 achieved an unprecedented 16.87 mg/L under the conditions of a pulse potential of −0.6 V vs SCE, pulse width of 1 s, and a duty cycle of 50 %. It witnessed a 314.7 % upsurge compared to the constant mode system. This enhancement could be attributed to pulse primarily enhancing the non-Faradaic process by facilitating electron transfer at the three-phase interface on the electrode surface and promoting mass transfer of reactants. In the final section, a 99.99 % deactivation efficiency against E. coli within 60 min was obtained. [Display omitted] [ABSTRACT FROM AUTHOR]

• A ZIF-8-derived carbon (Z8C) supported Fe 2 P 2 O 7 electrocatalyst is fabricated. • The catalyst showed superior electroactivity for the four-electron ORR. • Its electrocatalytic performance and methanol tolerance are better than Pt/C. • XPS and XAS studies suggest an electron redistribution from Z8C to Fe 2 P 2 O 7. • DFT calculations show that the redistribution boosts the catalyst's intrinsic activity. Fuel cells promise high energy density and energy conversion efficiency but are plagued by the scarcity of platinum for facilitating the oxygen reduction reaction (ORR). Herein, a facile synthesis of a heterojunction electrocatalyst of ZIF-8 derived carbon (Z8C) supported Fe 2 P 2 O 7 (Fe 2 P 2 O 7 @Z8C) is reported. The electrocatalyst exhibited higher half-wave potential than the state-of-the-art Pt/C catalyst by more than 33 mV and achieved a peak power density of 152.47 mW cm−2, outperforming the Pt/C-driven cell by ca. 14.5 mW cm−2 in alkaline membrane electrode assemblies under similar operating conditions. X-ray photoelectron and X-ray absorption spectroscopic studies suggested a spontaneous electron redistribution across the heterojunction interface in Fe 2 P 2 O 7 @Z8C. Density functional theory calculations indicated that the electron redistribution may remarkably promote the intrinsic activity of Fe 2 P 2 O 7 @Z8C toward the four-electron ORR pathway. These findings offer an indispensable strategy for rational design of highly efficient and durable non-noble electrocatalysts. [Display omitted] [ABSTRACT FROM AUTHOR]

• Developed a series of transition metal (Fe, Co, Mn) and nitrogen co-doped carbons with a well-defined core-shell structure. • Hollow spherical carbons can anchor or trap metal and nitrogen atoms located at the corners and edges of carbon particles. • Fe- N- C@NSG exhibits a half-wave potential of 0.95 V (vs. RHE) in alkaline solution, surpassing that obtained by commercial Pt/C. • The long Fe- N bond, elevated d-band center and the more positive surface charge of Fe atoms can promote the ORR. Developing non-precious metal catalysts to replace Pt-based catalysts for oxygen reduction reaction (ORR) is a hotspot presently, and transition metal-nitrogen co-doped carbon (TM N C) materials have been deemed as the most promising candidates. In this work, chitosan-derived-curved-carbon covered natural spherical graphite (SG) with a well-defined core-shell structure were prepared via hydrothermal carbonization (HTC) process followed by activation under NH 3 atmosphere. A series of active transition metals (M=Fe, Co, Mn) and nitrogen atom were embedded into the curved carbon to form various M N C moieties on SG surface as active sites for ORR. Among the atomic precise M N C@NSG hybrid catalysts, the Fe N C@NSG shows the best ORR performance and the half-wave potential is 0.95 V (vs. RHE), which are 108 % as high as that obtained by commercial Pt/C in alkaline environment. Besides, the electrochemical stability and methanol tolerance of the catalyst is also superior to commercial Pt/C. DFT calculations reveals that the high-performance stems from the curved Fe N C units in the shell and high electrical conductivity of natural SG in the core for the typical core-shell structures. Moreover, the sluggish ORR kinetics can be efficiently accelerated by the increased Fe N bond length, more positive-shifted d-band center and more positive surface charge of active Fe atoms in the curved Fe N C units on spherical SG. This provides an enlightenment for developing efficient non-platinum group metal (PGM) catalysts using cheap and volume natural spherical graphite as building brick for energy storage and conversion devices. [ABSTRACT FROM AUTHOR]

Alkaline oxygen reduction reaction (ORR) presents an important role for energy conversion technologies and requires the development of an efficient electrocatalyst. Pt-based catalysts provide suitable activity; however, Pt production accessibility and high costs create hurdles to their commercial implementation. Fe coordinated within N-doped carbon materials (Fe N C) are a promising alternative due to their high ORR catalytic activity, although the currently commercially available Fe N C materials rely on harsh synthetic protocols which can lead to increased environmental impacts. In this work we target this issue by taking advantage of an oily sludge waste currently generated in refineries to synthesize Fe N C materials, thus, avoiding the environmental impact caused by the management of this waste. The solid particles within oily sludge, which present a high concentration of C and Fe, were combined by different nitrogen sources and pyrolyzed at high temperatures. The prepared materials present a hierarchical pore structure with surface areas up to 547 m2 g−1. X-ray photoelectron spectroscopy analysis found that the impregnation of N using phenanthroline promotes the formation of pyridinic-N structures, which enhances the ORR performance compared to melamine doping. Additional doping of Fe with phenanthroline results in an ORR mass activity of 1.23 ± 0.04 A g FeNC −1 at 0.9 V RHE, iR-free in a rotating disc electrode (0.1 M KOH). This catalyst also shows a lower relative loss in activity at 0.9 V RHE after 8000 cycles in O 2 -saturated conditions compared to a commercial FeNC catalyst, PMF D14401, (−63.5 vs −69 %, respectively), demonstrating promise as a cheap and simple route to Fe N C catalysts for alkaline ORR. [Display omitted] [ABSTRACT FROM AUTHOR]

• Ultrathin 2D Al-MOF nanosheets were synthesized by a solvothermal method. • The presence of a mixed solvent and sulfate ion is critical to the formation of the specific 2D Al-MOF. • Ther ultrathin morphology is beneficial for the exposure of active sites and mass/electron transport. • The optimized Al-MOF exhibited high catalytic activity with almost no overpotential and high selectivity for 2e− ORR to H 2 O 2. Electrochemical transformation from oxygen reduction reaction (ORR) to hydrogen peroxide (H 2 O 2) is one of the promising green techniques to synthesis H 2 O 2. However, due to the competing two processes of 2e− and 4e−ORR with different products, designing and synthesizing highly selective and active 2e− ORR electrocatalysts for H 2 O 2 production is fundamentally and practically important. In this work, we used a simple solvothermal method and self-template strategy to create ultrathin 2D Al-MOF nanosheets for efficient electrocatalytic synthesis of H 2 O 2 by 2e− ORR. The presence of a mixed solvent and sulfate ion is critical to the formation of the specific structure. Naturally, their ultrathin morphology and abundant mesoporous formation leads to the sufficient exposure of electrochemically active sites and high mass/electron transfer capability. Therefore, the Al-MOF NSs show excellent electrocatalytic performance for 2e− ORR. The optimized Al-MOF NSs-1 exhibited the best ORR catalytic performance with almost no overpotential and high selectivity for 2e− ORR to H 2 O 2 (94 %–98 %) in a wide range of low potentials in alkaline electrolyte. Meanwhile, the high reaction rate of 2.56 molg cat −1h−1 for H 2 O 2 production has also been achieved at 0.6 V. Furthermore, the Al-MOF NSs-1 enable to catalyze H 2 O 2 production with excellent durability and selectivity after long-term stability test (10,000 cycles) and 11 h of potentiostatic electrolysis. The present study indicates the promising application of metal organic frameworks (MOFs) materials in H 2 O 2 electrochemical synthesis. [Display omitted] [ABSTRACT FROM AUTHOR]

The Rh(111) electrode shows superior oxygen reduction reaction (ORR) activity to Ir(111), contradicting the predicted trend based on the volcano plot. To unveil the origin for this, we investigate the interfacial structures of Rh(111) single crystalline electrode in 0.1 M HClO 4 and 0.5 M H 2 SO 4 solutions using cyclic voltammetry and potential step chronoamperometry under a hanging meniscus rotating disk electrode configuration. Our results reveal that i) in N 2 saturated solution even at a potential below 0.20 V, oxygen-containing species adsorbates can be formed on the Rh(111) surface probably generated by oxidation of water; ii) Even under mild conditions, multiple cycles and current transients in O 2 saturated solution at potentials where ORR taking place can cause significant surface disordering; iii) The disordering of the Rh(111) electrode induced by ORR exhibits similar base cyclic voltammograms to those of vicinal Rh(hkl) such as Rh(553) and Rh(332) etc., depending on the potentials applied during ORR, which, in turn, enhances the ORR activity in both 0.1 M HClO 4 and 0.5 M H 2 SO 4. These new findings provide valuable insights into the structure-performance relationship of ORR. [ABSTRACT FROM AUTHOR]

With hydrogen being projected as the fuel of the future, proton exchange membrane fuel cells (PEMFC) have regained prominence as a zero-emission power source. Researchers are focusing on replacing the conventional carbon support used for the platinum catalysts with alternative materials to improve the durability of the electrocatalysts. Despite being a potential candidate, graphene-based materials have been limited by their lower limiting current density, possibly due to restacking of the graphene sheets. On this note, we introduced varying quantities of metal-oxide based 1D TiO 2 nanowires to reduced graphene oxide (rGO) support and analysed their impact on the performance of the electrocatalyst. The optimized support with an initial content of 60 wt.% GO and 40 wt.% TiO 2 exhibited higher mass transfer limiting current density, after Pt incorporation (Pt/TiO 2 -rGO), in comparison to the other composites. The catalyst showed higher retention in electrochemical surface area (1.42 times) and mass activity (1.48 times) compared to the commercial Pt/C after an accelerated durability test. Polarization studies carried out in a 25 cm2 fuel cell fixture exhibited a peak power density close to 720 mW cm−2 and almost two times higher current density (at 0.6 V) than the catalyst without TiO 2. These results reaffirm the role of TiO 2 in overcoming the limitations of graphene-based support. [ABSTRACT FROM AUTHOR]

• A novel layered cobalt oxide Ba 2 Co 9 O 14 is developed as a bifunctional oxygen catalyst. • Ba 2 Co 9 O 14 based ZAB shows an excellent maximum power density of 166 mW cm−2 with good cycling stability. • Ball-milling treatment exhibits increased specific surface area and enlarged pore size. • Ball-milling benefits the enhancement of the ZAB. In this work, a layered cobalt oxide Ba 2 Co 9 O 14 (BCO), belongs to a Ba n+1 Co n O 3n+3 (Co8O8) family composed by alternating CdI 2 based layers (Co8O8) with n (111) perovskite blocks (Ba n+1 Co n O 3n+3), has been developed as a potential bifunctional oxygen electrocatalyst candidate for efficient and durable rechargeable zinc-air battery (ZAB) application. Because of the greatly increased the specific surface area caused by ball-milling, the as-milled BCO material exhibits strongly enhanced bifunctional electrocatalytic activity towards oxygen reduction and oxygen evolution reaction in alkaline medium. Moreover, the assembled BCO-based ZAB yields an effectively improved maximum output power density of 166 mW cm−2, a considerable specific capacity of 789 mAh g −1, and excellent charge-discharge cycle stability of over 250 h at 10 mA cm−2 with over 1500 cycles. A layered cobalt oxide Ba 2 Co 9 O 14 (BCO) is a promising bifunctional oxygen electrocatalyst for efficient and robust rechargeable zinc-air battery, which is further enhanced by the ball-milling treatment because of the formation of more active reaction sites. [Display omitted] [ABSTRACT FROM AUTHOR]

The annual generation of coffee waste has overtaken 6 million metric tons, becoming a serious environmental problem. Herein, we report the fabrication of bimetallic electrocatalysts synthesized by 1) pyrolyzing spent coffee grounds (SCGs) at 400, 600, 800 and 1000 °C, 2) activating the as-obtained char with KOH and 3) functionalizing the activated carbon with iron(II) and manganese(II) phthalocyanine. The final electrocatalysts showed a high degree of amorphousness, defectivity (increasing with temperature) and high specific surface area (up to 1820 m2 g−1). In half-cell compartment (0.1 M KOH electrolyte), the top-notch material in terms of oxygen reduction reaction (ORR) activity and selectivity was CFeMn_600, which showed the same half-wave potential (E 1/2) compared to Pt/C standard along with a lower peroxide production. These outstanding results could be attributed to a high surface area, a Fe-Mn synergy, and an abundance of C-N defects. The performance of CFeMn_600 as a cathode material in alkaline exchange membrane fuel cells (AEMFC) showed an open circuit voltage (OCV) of 0.890 V and power density of 30 mW cm−2. Notwithstanding, this research is one of few cases where a waste-derived electrocatalyst is tested in a real AEMFC, thus becoming a pioneer in the fuel cell study of waste-derived electrode materials. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide production through the electrochemical two-electron oxygen reduction presents a compelling alternative to the anthraquinone process due to the cheap starting materials and low operating temperature and pressure. Transition metal species featuring with multi-active sites, offer high electrochemical activity and selectivity. MXenes, distinguished by excellent electrical conductivity and the two-dimensional structure facilitating smooth ion transportation, further enhance the prospects of this production approach. In this study, three Mo-based MXenes were synthesized: Mo 2 TiC 2 F x , Mo 2 Ti 2 C 3 F x and Mo 2 CF x. Among these, Mo 2 TiC 2 F x emerged as the most promising catalyst for 2e−ORR, achieving a remarkable H 2 O 2 yield of up to 0.54 mol·g cat −1·h−1. Moreover, it also exhibits a high H 2 O 2 selectivity ranging from 81.3 % at 0.2 V to 94.1 % at 0.6 V vs. RHE, coupled with an impressive faradaic efficiency of 76.4 % at 0.4 V using H-cell. Further analysis indicates that the superior 2e−ORR performance can be attributed to the presence of metallic Mo on the surface of Mo 2 TiC 2 F x. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide (H 2 O 2) is an innovative and environmentally friendly oxidant that finds wide-ranging applications across multiple industries. In the past, H 2 O 2 production predominantly relied on the anthraquinone method, which had drawbacks such as the generation of organic waste and the requirement for energy-intensive reactions. A cheap, efficient, and sustainable way of producing H 2 O 2 may be achieved through the redox reaction between oxygen and water. On both small and large scales, the electrosynthesis of H 2 O 2 is practical and affordable. In recent years, it has been thought that the energy-intensive anthraquinone process may be replaced by the electrochemical synthesis of H 2 O 2 via the two-electron oxygen reduction reaction (ORR) route. To eliminate the organic pollutants found in drinking water and industrial effluent, highly effective hydrogen peroxide (H 2 O 2) must be produced electrochemically using gas diffusion electrodes (GDEs). Compared to other carbonaceous cathodes, the GDEs as cathodic electrocatalysts demonstrate greater cost-effectiveness, lower energy consumption, and higher oxygen utilization efficiency for the formation of H 2 O 2. A promising alternative for enabling the growth of sustainable economics in the W&W sector is microbial electrochemical systems (MESs) that create H 2 O 2. To enhance the efficiency and predictability of H 2 O 2 production in MESs, a machine-learning approach was adopted, incorporating a meta-learning methodology to forecast the generation rate of H 2 O 2 in MES based on the seven input variables, comprising several design and operational parameters. [Display omitted] [ABSTRACT FROM AUTHOR]

• The natural sunlight was used to reduce the composite of graphene oxide and carbon nitride, and for creating Lewis active sites. • The first time use of analytical and electrochemical CO 2 adsorption/stripping studies to investigate the effect of Lewis active sites. • Post CO 2 stripping electrochemical studies to corelate active site performance in terms of electrochemical active surface area (ECSA), active site density (ASD), turn over frequency (TOF) and mass activity (MA). • DFT study results highlighting the catalyst's structure and its impact on lowering the overpotential for ORR. Developing cost-effective and highly active oxygen reduction reaction (ORR) electrocatalysts is crucial for advancing fuel cell (FC) technology, but current efforts face challenges due to high cost and complex synthesis procedures. This study presents a rapid and cost-effective synthesis method utilizing solar radiation to prepare ORR electrocatalysts. The approach involves reducing a composite of 2-dimensional graphene oxide (GO) and porous graphitic carbon nitride (g-C 3 N 4) under solar radiation. This process creates Lewis base centers and a hierarchal porous structure with a high surface area, facilitating O 2 molecule diffusion and adsorption. The resulting electrocatalyst exhibits an onset potential of 0.85 V, follows a four-electron pathway for ORR, and demonstrates excellent methanol tolerance and stability compared to Pt/C. The catalyst's outstanding performance is attributed to abundant Lewis base active centers from g-C 3 N 4 on solar reduced GO (SRGO) sheets, optimized surface area, porosity, and a strong interface between electroactive Lewis centers and conductive graphitic domains. Density functional theory (DFT) results confirm the lower limiting potential of the Pyridinic N site, supporting ORR activity. This novel strategy, using sunlight as synthesis route, provides insights into structural properties, Lewis basicity, and enhanced electrochemical activity of high-performance N-doped carbon ORR catalysts. [Display omitted] [ABSTRACT FROM AUTHOR]

Enzymes with high efficiency and selectivity in biological catalysis have fuelled great interest in being utilized in catalysis apart from living organisms. Owing to the similarity between some enzymatic oxygen reduction reaction (ORR) and electrocatalytic four-electron (4e−) ORR processes in bonding with O 2 , electron transfer between catalysts and substrates/intermediates, and reduction processes from O 2 to H 2 O, enzyme-inspired ORR electrocatalysts have been widely studied. Notably, artificially synthesized molecular electrocatalysts inspired by enzymes can inhibit the limitations of low yield, limited sources, thermal instability, and poor reusability of the direct use of enzymes yet also exhibit high activity and robust stability over specific reactions. This minireview focuses on enzyme-inspired molecular electrocatalysts, especially cytochrome c oxidases and multicopper oxidases, for efficient electrocatalytic oxygen reduction. Furthermore, we outline the challenges and outlook needed to guide the design and application of enzyme-inspired molecular electrocatalysts for the ORR. [Display omitted] [ABSTRACT FROM AUTHOR]

• Atomically dispersed Fe and Cu sites with two-N-bridged decorated N-doped porous carbon is synthesized. • The fine structure of Fe 1 Cu 1 -NC is characterized by AC-HAADF-STEM and XAFS. • The Fe 1 Cu 1 -NC catalyst exhibits a comparable ORR activity to Pt/C with excellent methanol tolerance and stability. • DFT calculation indicates that the synergistic effect between Fe and Cu is preferable for modulating ORR activity. The sluggish reaction kinetics of oxygen reduction reactions (ORR), combined with a long-standing dependence on expensive and unstable platinum-based catalysts, has significantly hindered the progress of sustainable energy solutions. Here, we have developed an atomically dispersed bimetallic FeCu-loaded N-doped porous carbon (Fe 1 Cu 1 -NC) catalyst for remarkable ORR efficiency. X-ray absorption fine structure (XAFS) analysis accurately determines that the coordination state of atomically dispersed Fe-Cu sites is a two-N-bridged with N 6 ligand. Fe 1 Cu 1 -NC has demonstrated superior ORR performance in alkaline environments when compared to commercial Pt/C catalysts. Notably, Fe 1 Cu 1 -NC exhibits a higher power density and specific capacity than Pt/C in zinc-air batteries. Density functional theory (DFT) calculations further confirm that the improved performance is due to the combined action of Cu and Fe single atoms, which results in a negative shift of the d -band center energy of Fe and facilitates activation of ORR intermediates. Atomically dispersed dual-metal with two-N-bridged FeCu-N 6 sites can lead to a negative shift in the d -band center of Fe, resulting in a weakening of the adsorption strength of intermediate species and enhancing the ORR performance in comparison to Pt/C. [Display omitted] [ABSTRACT FROM AUTHOR]

• Electronic agglomeration effect on CoO/CNT is achieved by atomic surface engineering. • DFT reveals F− induces electron increased in Co-O site, leading to high density of Co. • F−CoO/CNT enables an advanced HSAB with low overpotential gap of 0.14 V. • This work offers a new way about electronic structure adjustment to design catalysts. Hybrid sodium–air batteries (HSABs) offer a possible solution for large−scale energy storage due to high theoretical energy density and abundant sodium resource. However, ORR suffers from sluggish kinetics with multielectron transfer step, resulting in high overpotential. Herein, we demonstrated electronic agglomeration effect on CoO/CNT to controllably activate catalytic active species to boost ORR by atomic surface engineering. By virtues of superior electron transfer ability and optimal adsorption energy of reactive species, activities of F− surface‐decorated electrode could be greatly improved. DFT revealed that F− induced electronic agglomeration on Co-O sites, resulting in high electron density of Co and intense combination with OH* in the first step. Surprisingly, the F−CoO/CNT showed favorable ORR activity and enabled advanced HSAB with low overpotential gap of 0.14 V. This work provides a new view about atomic and electronic structure engineering for activating active species, which will pave a new way for designing electrode materials. [Display omitted] [ABSTRACT FROM AUTHOR]

• Pt and Ni dissolution mechanisms are morphology-independent. • Pt and Ni dissolution rates are morphology-dependent. • Increased Pt and Ni dissolution rate above 1 V versus RHE. • In situ ICP-MS evidence of Pt-skeleton nanostructure formation. • Long AST needed for steady state dissolution and catalyst's lifetime prediction. An electrochemical flow cell combined with inductively coupled plasma mass spectrometry (FC-ICP-MS) is a powerful tool to understand the mechanisms of metal dissolution and to develop mitigation strategies. Herein, we quantified in situ the amount of Pt and Ni atoms dissolved from PtNi/C nanocatalysts employed to electrocatalyze the oxygen reduction reaction (ORR) in proton-exchange membrane fuel cell cathode. The nanocatalysts feature similar crystallite size and Pt:Ni atomic ratio but different morphologies (spheres, octahedra, sponges). The FC-ICP-MS results reveal that the nanocatalyst morphology affects the dissolution rate of Pt and Ni but not the dissolution mechanism. They also provide analytical evidence that dissolution of Pt atoms is consistently accompanied by the dissolution of Ni atoms exceeding the stoichiometric composition. Furthermore, we demonstrate that ex situ acid leaching mitigates, but does not entirely prevent, the electrochemical dissolution of Ni atoms. Stabilized Pt and Ni dissolution rates were achieved after a one hour long accelerated stress test (AST). We provide evidence that the Pt dissolution rate remains constant before and after the AST. In contrast, the dissolution rate of Ni decreases by a factor of 10 following the AST. Among various nanoparticle shapes, spherical PtNi/C nanoparticles offer the best solution regarding the Pt and Ni retention compared to other nanoparticle shapes. [Display omitted] [ABSTRACT FROM AUTHOR]

• Redox properties of tetrapyridylalkylamine Cu(II) complexes with diimines. • Oxygen reduction catalysis by tetrapyridylalkylamine Cu(II) complexes with diimines. • Catalytic oxygen reduction mechanism by tetrapyridylalkylamine Cu(II) complexes with diimines. Oxygen reduction reaction (ORR) is important in artificial energy conversion systems such as fuel cells. However, it is kinetically sluggish. It is thereby highly desirable to develop ORR catalysts to improve the efficiency of energy conversion. In this work, three copper(II) complexes based on the hexadentate tetrapyridylalkylamine N,N,N',N'-tetrakis(2-pyridyl-methyl)-1,4-butanediamine (tpbn), namely [Cu 2 (tpbn)(CH 3 OH) 4 (ClO 4) 2 ](ClO 4) 2 (Cu-tpbn), [Cu 2 (tpbn)(bpy) 2 ](ClO 4) 4.2CH 3 COCH 3 (Cu-tpbn-bpy, bpy = 2,2′-bipyridine), and [Cu 2 (tpbn)(Me 2 bpy) 2 ](ClO 4) 4.3CH 3 CN (Cu-tpbn-Me 2 bpy, Me 2 bpy = 4,4′-dimethyl-2,2′-bipyridine), were prepared and their catalytic properties for ORR studied. All three complexes were homogeneous electrocatalysts for ORR in neutral phosphate buffer solutions. The ORR mediated by Cu-tpbn-Me 2 bpy had the most positive onset potential of 0.461 V vs RHE. In the applied potential window of -0.19 – 0.50 V vs RHE, Cu-tpbn boosted the stepwise four-electron ORR to mainly produce H 2 O, whereas Cu-tpbn-bpy and Cu-tpbn-Me 2 bpy mediated the ORR to mainly generate H 2 O 2. The rate constants for the ORR to H 2 O promoted by Cu-tpbn, Cu-tpbn-bpy and Cu-tpbn-Me 2 bpy were 1.2 × 103 s−1, 3.2 × 10 s−1 and 7.8 × 10 s−1, respectively. The foot-of-the-wave analysis showed that the turnover frequencies for the reduction of O 2 to H 2 O 2 mediated by Cu-tpbn, Cu-tpbn-bpy and Cu-tpbn-Me 2 bpy were 1.5 × 104 s−1, 7.5 × 10 s−1 and 2.7 × 102 s−1, respectively. Meanwhile, complexes Cu-tpbn-bpy and Cu-tpbn-Me 2 bpy were more stable than Cu-tpbn. This work unveiled that the catalytic activity and the product selectivity of the ORR were greatly associated with the denticity, the steric effect and the electronic property of the organic ligands. Three tetrapyridylalkylamine copper(II) complexes were homogeneous catalysts for oxygen reduction reaction (ORR). The main product of ORR mediated by the Cu-tpbn systems was directed from H 2 O to H 2 O 2 via the incorporation of the diimine ligands. [Display omitted] [ABSTRACT FROM AUTHOR]

• The carbon materials (OC-R/CNT) with quinone group were synthesized using rhein and carbon nanotube as the precursors by one-step pyrolysis. • The OC-R/CNT displayed high selectivity, high production rate, good long-term stability and reusability as an electrocatalyst for the 2-e oxygen reduction reaction to synthesize H 2 O 2 in neutral medium. • The H 2 O 2 solution produced in situ showed good antibacterial activity implying the practicability of OC-R/CNT. Oxygen-doped carbon materials (OC) have been studied as the electrocatalysts of two-electron oxygen reduction reaction (2-e ORR) to synthesize H 2 O 2 due to their low cost and high selectivity. In this study, quinone group contained OC (OC-R/CNT) were prepared using the mixture of rhein with quinone group and carbon nanotube (CNT) as the precursor via one-step pyrolysis. The RRDE test showed that the OC-R/CNT gave a H 2 O 2 selectivity of 94 % at 0.20 V in neutral medium. During the H-cell test, the H 2 O 2 yield of OC-R/CNT can be up to 170 mmol g cat −1 h−1 at 0 V vs. RHE and the OC-R/CNT catalyst exhibited good long-term stability and reusability. The H 2 O 2 solution produced at 0 V vs. RHE for 1 hour showed good bactericidal properties. For comparison, the OC without quinone group (OC-G/CNT) were also prepared with glucose and CNT as the precursor under the same condition, which showed poorer 2-e ORR catalytic performance. This study not only provides a feasible method to prepare quinone group contained carbon materials but also verifies the important role of quinone group in 2-e ORR. [ABSTRACT FROM AUTHOR]

• O-Pt 3 Co/CT catalysts are synthesized via repetitive absorption/chemical reaction method. • O-Pt 3 Co/C700 displays an ordered structure with enriched Pt shell. • O-Pt 3 Co/C700 shows a mass and specific activity of 0.53 A mg Pt −1 and 0.91 mA cm−2. Thermal annealing at high temperatures is usually employed to alloy Pt with transitional metals to produce structurally ordered intermetallic electrocatalysts for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells. The most important issue to address in this approach is the particle aggregation during thermal annealing. Herein, the repetitive absorption/chemical reaction method is used to prepare zeolitic-imidazolate-framework-coated carbon and alloy particles by simply soaking an ordered Pt 3 Co (O-Pt 3 Co) sequentially in Co(NO 3) 2 and 2-methylimidazole solutions at room temperature. The as-prepared catalysts display impressive ORR activity and stability relative to their commercial Pt/C counterpart. The optimized catalyst demonstrates a mass and specific activities of 0.53 A mg Pt −1 and 0.91 mA cm−2, respectively. In addition, no obvious decay is observed after 30 000 voltammetric cycles from 0.6 V to 0.9 V. The mechanism study shows that Co and doped N play a key role in promoting ORR activity and stability. [Display omitted] [ABSTRACT FROM AUTHOR]

• At Fe phthalocyanine modified electrodes, different anions affect the Fe(III)/(II) formal potential and the onset potential for the ORR electrocatalysis. • Depending on the electrolyte media a transition from inner (ISET) to other sphere electron transfer (OSET) mechanism is detected. • In alkaline media almost no anion adsorption is detected, if contrasted with acid media. Fe phthalocyanine with carbon nanotubes (FePc-CNT) has been used as catalysts for ORR using the following supporting electrolyte: 0.1 M NaOH, 1 M NaOH, 1 M HNO 3 , 1 M HClO 4 , and 1 M HBr. The thermodynamic and kinetic information was acquired from cyclic voltammetry in N 2 saturated media, and then polarization curves saturating with O 2. The rate-determining step is modulated by the formal potential (E 0' Fe(III)/(II)) in basic media, coherent with the inner sphere electron transfer mechanism. However, in strong acid electrolytes, the Tafel slope value is ∼ -0.090 V dec−1 at low overpotentials and ∼ -0.120 V dec−1 at high overpotentials indicating that a poisoning process is hampering the ORR, and causing an outer sphere electron transfer mechanism. Impedance spectroscopy and poisoning test (recovery of the activity of the catalyst in NaOH after initial use in acid) support the thesis of ion adsorption/poisoning for the low electrocatalytic activity of FePc based catalysts in acid media. [Display omitted] [ABSTRACT FROM AUTHOR]

In order to investigate stability of oxygen reduction reaction (ORR) on a Pt 3 Y thin film under relevant fuel cell conditions, we performed an accelerated stress test (AST) consisting of 3600 potential cycles between 0.4 and 1.4 V at 1 V s−1 in a single proton exchange membrane fuel cell (PEMFC). The ORR activities were evaluated via polarization curves before and after the AST. Electrochemical active surface area (ECSA) was obtained by CO-stripping voltammetry whereas the morphological changes were monitored by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Variations in surface composition and electronic structures were evaluated by energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). After AST, the polarization curves show loss of ORR activity in all voltages for both Pt and Pt 3 Y. Except at very high voltages (E > 0.85 V RHE), the ORR activity of Pt 3 Y after AST is very close to that of Pt before AST. This correlates well with the results from the deconvolution of Pt-4f XPS spectra where the binding energy of metallic Pt in Pt 3 Y is comparable to pure Pt (71.22 eV). SEM and TEM images demonstrate that the morphologies of the aged Pt 3 Y and as-sputtered Pt are similar, whereas EDX results confirm a steady bulk composition of Pt 3 Y thin films throughout the entire electrochemical test. By correlating all these results, we conclude that the loss of ORR activity for Pt 3 Y is due to an increase in the thickness of the Pt overlayer which induces a relaxation of the Pt overlayer decreasing the compressive strain effect. For pure Pt, the loss of ORR activity is associated with a growth of the Pt domains associated with Ostwald ripening process. [ABSTRACT FROM AUTHOR]

The production of H 2 O 2 by oxygen reduction reaction (ORR) is low energy consumption and environmentally friendly. Pd/C is an effective electrocatalyst for oxygen reduction, while its selectivity is low due to a tendentious four-electron pathway ORR process. The limited reserves of palladium and inevitable corrosion issue of carbon support add extra obstacles toward practical application. In this work, Pd nanoparticles with 3–5 nm were synthesized on MXene sheets. Results indicated that Pd/MXene exhibited 3.5∼4.2 times ring current than Pd/C and much higher H 2 O 2 selectivity. The H 2 O 2 yield of Pd/MXene was measured to be 1.43 mol g−1 h−1. The excellence in electrochemistry was from the synergistic effect of Pd and MXene. The existence of MXene increases metallic Pd on the surface. This study on MXenes as supports of Pd nanoparticles for two-electron oxygen reduction provides extensive reference significance to H 2 O 2 generation. [ABSTRACT FROM AUTHOR]

• Triazines enhance oxygen reduction activity of a Pt catalyst. • The dependence of the enhanced activity on the triazine concentration is explained. • Aminotriazines enhance the durability of a Pt catalyst. • Aminotriazines mitigate size increase of Pt nanoparticles after a durability test. The effects of triazines on the oxygen reduction reaction activity and durability of Pt/C were examined. Pt/C treated with triazines besides melamine exhibited lower ORR activity than that treated with melamine. Triazines, with the exception of melamine, were not strongly adsorbed on the Pt surface, and the weak interaction with Pt/C resulted in a low enhancement effect. In contrast, when triazines were dissolved in an electrolyte solution, a strong enhancement effect (> 4-fold at an optimized concentration) was observed because they were supplied from the solution. The dependence of activity on the concentration of triazine in the solution was also examined. The concentration at which maximum activity is observed varied based on the triazine used, reflecting the strength of the interaction between triazines and Pt. Furthermore, triazines with amino group(s) considerably enhanced the durability of Pt/C, whereas cyanuric acid without an amino group did not suppress degradation. While the surface area of Pt decreased by 63 % after a degradation test (0.6 V(3 s)–1.0 V(3 s), 10,000 cycles, at 80 °C) in the absence of triazines, it only decreased by less than 20 % in the presence of aminotrizines. Transmission electron microscopy observations clearly show that aminotriazines significantly attenuated the increase in the Pt nanoparticle size after the degradation test. Cyclic voltammograms of Pt/C in the presence of aminotriazines suggested that the suppression of degradation may be due to the suppression of the Pt surface oxidation and the protection of vulnerable sites on Pt nanoparticles. [Display omitted] [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) is a crucial process for energy conversion and storage devices. Despite platinum (Pt) being the state-of-the-art material for ORR, the limited performance of Pt-based catalyst, Pt scarcity, and vulnerability of global supply chains for critical minerals, have made it imperative to develop alternative electrocatalysts that either contain no precious metals at all or require only a very low loading of these valuable resources. In this study, we demonstrate that the incorporation of co-dopants, nitrogen (N) and boron (B), with a dissimilar electronegativity is a promising approach to develop metal-free electrocatalysts for ORR. We discovered that the interaction between N and B plays a vital role in both (i) incorporating the dopants in high-curvature carbon nano-onions (CNOs) and (ii) promoting ORR performance. Tuning the annealing temperature was crucial to achieve a desirable N-B chemical configuration and synergistic effects of N and B on ORR catalysis. Our investigation revealed that N,B-doped CNOs prepared at 700 °C exhibit the best ORR performance in 0.1 M KOH with a dominant 4-electron pathway and excellent durability. Based on X-ray photoelectron spectroscopy (XPS), Raman analysis, and high-resolution scanning transmission electron microscopy (HR-STEM), we conclude that abundant N and B sites, especially N-C-B (isolated) sites, at the edges in conjunction with high surface activity of CNOs are responsible for such outstanding performances. This study provide insights into the design of metal-free catalysts for efficient ORR catalysis, and the importance of alternative electrocatalysts in the current global supply chain disrutipn scenario. [ABSTRACT FROM AUTHOR]

Here, we investigate the oxygen reduction reaction activity of near-monocrystalline platinum nanoflowers presenting a low microstrain to decorrelate the contribution of (i) distorted lattice and (ii) high coordination active sites found within the platinum nanoflower pores to the specific activity enhancement. The results are discussed within the framework of previous investigations onto various catalytic nanostructures. We evidenced that the microstrain of the platinum nanoflowers stands out of the trends previously established for defective platinum-based nanostructures, where the activity is driven by lattice distortion. This indicates that (i) 'defective' structures with low lattice distortion, but high variation in coordination number, can be synthesized and (ii) that their specific activity improvement is comparable to the surface distortion approach in liquid electrolyte. [ABSTRACT FROM AUTHOR]

• Highly durable and performing bifunctional alkaline Zn-air battery air electrodes. • Bifunctional GDEs, based on α-MnO 2 nanorods for ORR and Ni/NiO nanoparticles for OER. • Structural and spectral-imaging characterization of GDEs: pristine and post mortem. • Degradation mechanisms understood with STXM-based chemical-state mapping and TEM. • Molecular-level study of role of Zn2+ in electrolyte in electrocatalyst degradation. Electrically rechargeable alkaline zinc air batteries (RZAB) – currently still at the R&D stage –, have great potential for stationary, as well as prospectively mobile, electrochemical energy storage applications. Their chief appeal is that they are made of abundant, environmentally friendly, intrinsically safe, and cheap materials, with established recycling concepts and auspicious life-cycle costs. One of the key weak points of present-generation RZAB programs is the air gas-diffusion electrode (GDE). In fact, on the one hand, GDE fabrication and testing are generally based on poorly understood protocols, and, on the other hand, performance is challenged by efficiency and durability issues. This work is centred on the fabrication of a novel bifunctional GDE for the air side of RZABs, on the assessment of its electrochemical performance and on the identification of factors impacting its efficiency and durability. The electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are α-MnO 2 nanowires and Ni/NiO nanoparticles, respectively. The composition of the active layer was optimized with rotating ring-disc electrode (RRDE) electrocatalysts tests. The GDEs were fabricated by spray-coating an ink, formulated with the electrocatalysts and the PTFE binder in an aqueous matrix. Fabrication and functional performance of GDEs – in pristine form and after ageing under realistic RZAB conditions – are rationalized on the basis of Scanning Electron Microscopy (SEM), Scanning Transmission X-ray SpectroMicroscopy (STXSM) at the Mn l -edge and Transmission Electron Microscopy (TEM) analyses. Imaging and spectral imaging disclosed the morphological and chemical-state evolution, brought about by electrochemical cycling. Special attention was devoted to the understanding of the role played by the presence of zincate in the electrolyte on the performance and ageing of the reversible air electrodes. [Display omitted] [ABSTRACT FROM AUTHOR]

Despite their potential as electrocatalysts, the catalytic mechanisms of main-group single-atom catalysts (MSACs) remain largely unexplored. To address this knowledge gap, we conducted a series of first-principles calculations to investigate a repertoire of MSACs that incorporated 17 active main-group atoms and 8 carbon supports, systematically screening the optimal catalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) via activity-adsorption scaling relations. Our findings reveal that as the single-atom in MSACs moves down the periodic table, their adsorption capabilities become even more enhanced. Moreover, MSACs derived from the fifth and sixth periods exhibit mild adsorption capabilities and robust catalytic activity. In addition, our study identifies a linear correlation between the adsorption energy of *OH intermediates, the p -band center, and the electronegativity of the main-group atom in MSACs, serving as an efficacious ORR activity descriptor and allowing for the prediction of novel catalysts. Our analysis further illuminated two distinct interaction patterns of MSACs with oxygenated species, elucidated through studying the p x - and p z -band centers and the resulting effects of orbital hybridization. Moreover, we successfully delineated the regulator role of carbon support species in enhancing the adsorption abilities of MSACs. By strategically pairing the appropriate main-group atoms with suitable carbon supports, we propose an innovative approach for the design of high-performance MSAC catalysts. [ABSTRACT FROM AUTHOR]

The electrocatalytic oxygen reduction reaction (ORR) is the key bottleneck of fuel cells and rechargeable metal-air batteries, and recently, metal nitrogen complex carbon (M N C) demonstrates great potential in these fields. However, the complex and easily degraded M N C structure often results in inferior activity and poor durability in electrolysis. Herein, we fabricate a catalyst of h-CeO 2 @CoNC through the extended Stöber method and subsequent pyrolysis, involving the hollow CeO 2 as the core and Co N C as the shell. The h-CeO 2 @CoNC catalyst exhibits notable ORR catalytic performances in 0.1 M KOH with a half-wave potential of 0.82 V and excellent durability, attributed to the synergistic interaction between CeO 2 and Co N C matrix. Specifically, the inner layer of CeO 2 is principally responsible for enhancing the chemical stability and the outer one of Co N C matrix is beneficial to boosting the ORR catalytic activity. This work provides an efficient preparation approach and further insight of rational design of the unique M N C catalysts for energy storage. [ABSTRACT FROM AUTHOR]

This study delves into the potential of MB 36 clusters (where M = Fe, Co, Ni) supported on graphene as effective single-atom catalysts (SACs). Our research is methodically segmented into several stages, each designed to validate the feasibility of the proposed material. We begin by investigating the potential energy surface of MB 36 clusters. Our findings reveal a preference for metallic atoms to position themselves above the central hexagonal vacancy of the B 36 cluster. This factor significantly contributes to the stabilization of the resultant MB 36 system. Subsequently, we employ ab-initio molecular dynamic simulations to affirm the stability of the graphene-supported MB 36 clusters. In the final stage, we evaluate the system's catalytic capability for the oxygen reduction reaction (ORR) by calculating the dissociation energy of O 2 and OOH post their adsorption on the M atom of the graphene-supported MB 36 cluster. These simulations suggest that FeB 36 could maintain stability at room temperature, exhibiting activation energies for O 2 and OOH dissociation lower than those previously reported on Fe/N/C-type SACs, approaching those found on the Pt(111) surface, the most efficient ORR electrocatalyst. This computational study suggests that graphene-supported FeB 36 clusters could emerge as a promising candidate for SACs. [Display omitted] [ABSTRACT FROM AUTHOR]

Using reactivity predictors to enhance or control the electrocatalytic activity of materials is a fascinating concept. This is especially true for the development of alternative platinum metal group-free materials as it facilitates the rational design of active catalytic materials for the oxygen reduction reaction (ORR). In previous work, we have found that the peripheral and non-peripheral electron-withdrawing effects and the electron-pull effect from axial extraplanar ligand in iron-phthalocyanine (FePc) are key factors in improving the binding energy between the active Fe site and O 2 resulting in an increase of the electrocatalytic activity of FePcs for the ORR. In this work, we have utilized fundamental principles of electrocatalysis and DFT calculations to design and synthesize FeN4 molecular catalysts to increase their catalytic performance for the ORR through the "pull" effect. To achieve this, by chemical synthesis, we have incorporated pyridinium functional groups (N+py) in peripheral and non-peripheral positions into the porphyrazine cyclic ligands. In this fashion we obtain the porphyrazinium molecular catalysts, [Fe(II)2,3-(TMe)TPyPz]4+ and [Fe(II)3,4-(TMe)TPyPz]4+. Because these new compounds are not commercially available and, to the best of our knowledge, they have not been tested for ORR. In order to determine their effectiveness, we have compared porphyrazinium with neutral analog porphyrazine compounds (Fe(II)TPyPz) and perfluorinated and perchlorinated iron phthalocyanines, which are currently the best molecular catalysts for ORR. The electrocatalytic activity was determined for each molecular catalyst deposited on the edge plane of a graphite electrode (EPG) surface in an alkaline medium. Only for the purpose of comparison we include two Fe porphyrins studied previously, which show low activity for ORR. Although the DFT theoretical analysis of porphyrazinium complexes suggests a high activity for these catalysts, our experimental findings revealed the opposite trend. Therefore, this finding makes us reconsider the interfacial effects, such as the counter-ions effects on N+ py that could influence the electron-pull effect, opening new insights for designing molecular catalysts considering interface engineering. Moreover we report for the first time, the reactivity linear relationship between the metal-centered redox potential gap (E° Fe(III)/(II) – E° Fe(II)/(I))) with the electrocatalytic activity for ORR for all catalysts studied, emerging this potential gap as a possible and promising new reactivity descriptor for ORR in MN4 catalyst. [Display omitted] [ABSTRACT FROM AUTHOR]

• The Fe/NSC-800 catalyst was prepared with a simple and green way. • The introduction of heteroatoms (N, S) through N-rich and S-rich precursor provides more defects and active sites for the electrocatalyst. • Electrocatalyst Fe/NSC-800 has excellent ORR performance and practical application prospects for Zn-air batteries. Currently, the scientific community is keenly interested in the design and production of efficient and durable transition metal electrocatalysts for oxygen reduction reactions (ORR). Therefore, this study reports a simple and reproducible N and S co-doped two-dimensional (2D) hierarchical porous electrocatalyst is reported. NSC the support material first was obtained by pyrolyzing trithiocyanuric acid (TTCA) and loaded on hemin to obtain the final material named Fe/NSC-800. 2D hierarchical porous structures with the large specific surface area were constructed by using TTCA as the template, S source, and additional N source. The addition of hemin not only retained the morphology of the NSC but also provided source of Fe for Fe/NSC-800. The Fe/NSC-800 possessed the limiting current density of 5.85 mA cm–2 and good ORR stability in 0.1 M KOH solution. Based on the excellent ORR performance of Fe/NSC-800, it was assembled into the primary Zn-air battery, which also exhibited satisfactory open circuit voltage (1.55 V) and energy density (880 W h kg–1). This work has contributed to the rational engineering and fabrication of high-performance ORR electrocatalysts for Zn-air battery applications. [Display omitted] [ABSTRACT FROM AUTHOR]

The structural and electronic characteristics of FeN4 are the determining factors in the catalytic performance of heat-treated Fe-N-C materials, as they serve as active sites. The insertion of heteroatoms as co-dopants (B, S, halogens) can induce electronic effects in the carbon matrix that improves their ORR catalytic activity. Therefore, it has become essential to combine experimental studies with DFT approaches to rationally design this type of catalyst. In this work, we evaluated by means of first principle DFT approaches, the ORR activity for the Fe(phen) 2 N 2 moiety including atoms/functionalities with different atomic radii and electronegativity, to resemble co-doped Fe-N-C -R catalysts. The results showed that the inclusion of halogens heteroatoms (-F, -Cl , and -Br) in the graphitic N C surrounding the FeN4 core could improve its ORR activity in terms of Fe-O 2 binding energy that is related to the Fe(III)/Fe(II) formal potential and, in consequence, with the on-set potential for the ORR. The high expected ORR activity is obtained for bromide co-doped FeN4 catalyst (FeN4-C-Br) since -Br atoms act synergistically, inducing long- and short-range electronic effects over both the FeN4 unit and N-pyridinic-like functions that change the electronic distribution over the aromatic N C structure modulating the Fe acidity, Fe-O 2 binding, and Fe-O 2 orbital interaction. [Display omitted] [ABSTRACT FROM AUTHOR]

It has been identified that the oxygen reduction reaction (ORR) is an extremely vital process for sustainable energy supply and sufficient chemical productions. In order to explore noble metal-free catalysts, instead of noble Pt, for ORR to overcome sluggish kinetics, much amazing and interesting research progress has been made in the past decades. Recently, owing to the intrinsic merits of tunable single-atom coordination structures, biomimetic active sites and comparable catalytic activity with Pt, transition metal-nitrogen-carbon (M–N–C) materials have been considered as one of the most promising catalysts toward ORR. Herein, regarding the critical role of activating and supporting oxygen (ASO) in the M–N–C materials toward ORR performances, a comprehensive review of the most recent significant research breakthroughs, remaining challenges and perspectives is timely presented in this work. Firstly, mechanism pathways of ORR catalyzed by M–N–C materials are displayed. Also, for boosting the intrinsic 4 e− /2 e− ORR activity and selectivity, influence of manipulating the microenvironments in the M–N–C catalysts is overviewed at length. Subsequently, the role of ASO in the M–N–C catalysts is systematically summarized. Then, the methods of oxygen identification and introduction are addressed in detail to achieve the M–N–C materials with outstanding electrochemical catalytic performances. Last but not the least, opinions/points of view for remaining challenges of the M–N–C catalysts are given. In closing, future directions of the M–N–C catalysts for ORR and other analogous reactions are proposed. [ABSTRACT FROM AUTHOR]

The incessant and drastic growth of global energy demand make it imperative to develop new affordable high-quality materials at a large scale to act as powerful electrocatalysts (ECs) on the relevant energy reactions. Here, we report the synthesis and characterization (FTIR, Raman, XPS, XRD, TEM and SEM) of new engineered electrocatalysts based on situ co-precipitation of Co 3 O 4 or Mn 3 O 4 nanoparticles in the presence of N, S-doped graphene (Co/N 3 S 3 -GF and Mn/N 3 S 3 -GF). The nitrogen, sulphur dual-doped graphene was achieved by a scalable dry ball-milling procedure followed by thermal treatment using graphene flakes as carbon source and trithiocyanuric acid as the precursor. The three materials prepared were applied as electrocatalysts for the oxygen reduction reaction (ORR) and demonstrated excellent electrocatalytic performance in alkaline medium with Co/N 3 S 3 -GF and Mn/N 3 S 3 -GF presenting onset potentials of 0.87 V vs. RHE. These were comparable to Pt/C onset potential (0.91 V). All materials showed good diffusion-limiting current densities (−3.49 to −4.17 mA cm−2) and selectivity for the 4-electron O 2 reduction to H 2 O. Furthermore, the Co/N 3 S 3 -GF and Mn/N 3 S 3 -GF electrocatalysts presented good tolerance to methanol poisoning and good stability with current retentions (76–81%). The approach followed in this work showed that affordable, simple and scalable procedures can be applied to develop ORR electrocatalysts with enhanced performances. • N,S dual-doped graphene was successfully prepared by scalable ball-milling method. • Co/N 3 S 3 -GF and Mn/N 3 S 3 -GF electrocatalysts showed excellent ORR performance. • Good stability/durability and tolerance to methanol crossover were achieved. [ABSTRACT FROM AUTHOR]

Understanding the kinetics of oxygen reduction reactions (ORRs) over non-precious-metal (NPM) catalysts in alkaline media is quite important for commercializing anion exchange membrane fuel cells. Rotating ring-disk electrode (RRDE) voltammetry has been useful for studying the selectivity of ORR, but typical analytical models might overestimate the four-electron pathway. The present study investigated ORR in alkaline media over Fe/N/C and N/C catalysts, which were prepared by pyrolyzing polyimide nano-particles. The obtained data were analyzed using the novel RRDE theory, which involves the Nabae model to distinguish a genuine four-electron reduction from a quasi-four-electron reduction (two plus two-electron reduction). The results demonstrated that the reduction with the Fe/N/C catalyst proceeded via an inherent four-electron pathway while that with the N/C catalyst prepared by a similar method proceeded majorly via a two-electron pathway. Image 1 • The kinetics of ORR in alkaline media over Pt-free catalysts was studied. • A novel RRDE theory with Nabae model was applied. • ORR over an N-doped carbon catalyst proceeded via a 2 + 2 electron pathway. • Fe/N/C catalyst exhibited a genuine 4 electron pathway. [ABSTRACT FROM AUTHOR]

Heteroatom doped carbon materials have been emerging as active materials for electrochemical energy generation and storage. The activity of such carbon materials is strongly depended the specific molecular structure of selected precursors and their synthetic strategy. Herein, we report an efficient bifunctional N, S co-doped carbon nanosphere(NS/C) via pyrolysis of poly (2,6-Diaminopyridine) spheres as precursor for the first time, in which 2,6-Diaminopyridine was polymerized in water using ammonium persulfate as both initiator and sulfur source in the absence of templates and surfactants. The resultant NS/C exhibits uniformly spherical structure filled with hierarchical pores, outstanding electronic conductivity and highly effective doping content of N(4.02 at%) and S(0.87 at%) elements. Electrochemical measurements demonstrate that the NS/C not only exhibits outstanding specific capacitance of 800 F/g in 6.0 M KOH and 710 F/g in 1.0 M H 2 SO 4 , but also displays excellent catalytic performance for oxygen reduction reaction (ORR) with the onset potential at 1.01 V vs RHE and the half-wave potential at 0.85 V vs RHE in 0.1 M KOH, outperforming the activity of carbon materials previously reported. The superior electrochemical properties of NS/C is directly attributed to the synergetic effect of N,S co-doping and its excellent conductivity, accessibility, high specific surface area as well as hierarchical pore structure. Image 1 • N, S-co-doped carbon nanospheres were synthesized via pyrolysis of the self-polymerized compound of 2,6-Diaminopyridine. • The N, S-co-doped carbon nanospheres exhibit high charge storage capacity with high specific capacitance and highly efficient ORR catalytic performance. • Heterocyclic polymers with meta-amino group can be used to synthesize heteroatom doped carbon nanospheres by this method. [ABSTRACT FROM AUTHOR]

A future widespread application of electrochemical energy conversion and storage technologies strongly depends on the substitution of precious metal-based electrocatalysts for the high-overpotential oxygen reduction and oxygen evolution reactions. We report a novel Co/Co–Fe nanoparticles/N-doped carbon composite electrocatalyst (Co/Co x Fe y /NC) obtained by pyrolysis of CoFe layered double hydroxide (CoFe LDH) embedded in a film of a bisphenol A and tetraethylenepentamine-based polybenzoxazine poly(BA-tepa). During pyrolysis poly(BA-tepa) forms a highly conductive nitrogen-doped carbon matrix encapsulating Co/Co–Fe nanoparticles, thereby circumventing the need of any additional binder material and conductive additives. Optimization with respect to pyrolysis temperature, the CoFe LDH/BA-tepa ratio, as well as of the gas atmosphere used during the thermal treatment was performed. The optimized Co/Co x Fe y /NC composite material catalyst exhibits remarkable bifunctional activity towards oxygen reduction (ORR) and oxygen evolution (OER) reactions in 0.1 M KOH represented by a potential difference of only 0.77 V between the potentials at which current densities of −1 mA cm−2 for the ORR and 10 mA cm−2 for the OER were recorded. Moreover, the Co/Co x Fe y /NC composite material pyrolyzed in ammonia atmosphere exhibits promising stability during both the ORR and the OER. [ABSTRACT FROM AUTHOR]

Bifunctional catalysts for oxygen electrodes, active for both the oxygen reduction and evolution reactions (ORR, OER), are highly desirable for the development of electrochemical energy conversion devices. In this work, carbon-supported tantalum based catalysts were synthesized by a microemulsion procedure from tantalum ethoxide through a fast hydrolysis reaction followed by heat treatment. The nature and composition of the different tantalates and oxides (general formula Na a Ta b O c , with a/b = 0–1 and c/b = 2.5–3) relied on the concentration of ethanol as well as on the annealing temperature, with Na 2 Ta 8 O 21 as predominant crystal phase in all cases. High annealing temperatures resulted in a certain degree of oxygen substoichiometry, which creates defects responsible of electrocatalytic activity. The electrochemical response for the oxygen reduction and the oxygen evolution reactions in alkaline electrolyte (0.1 M NaOH) was evaluated for the first time in this type of materials. The presence of Na 2 Ta 8 O 21 phase over other oxides/tantalates, a high crystallinity of such Ta-phase, and the oxygen substoichiometry are the three parameters playing a relevant role to favor ORR and OER electro-activity. The best formulations were found in a trade-off situation using 3% ethanol and annealing at 900 °C. [ABSTRACT FROM AUTHOR]

It is highly essential to produce cost-effective and efficient multifunctional porous carbon materials for sustainable energy technologies. Here, we report a facile approach to synthesis biomass derived porous carbon having inherited heteroatoms by mechanochemical method and post pyrolyzing treatment. The optimized porous carbon exhibits superior oxygen reduction reaction performances in an alkaline electrolyte with a half-wave potential of 0.76 V (vs. reversible hydrogen electrode) with a small kinetic current density of 35.5 mV dec−1 and outsanding stability with great tolerance against methanol poisoning. It also shows the multifunctional capability of electrochemical energy storage as supercapacitor electrode material (coin cell), showing high gravimetric capacitance of 273 F g−1 in the aqueous electrolyte with superior cycling stability. [ABSTRACT FROM AUTHOR]

LaSrNiO nanoparticles with different doping amount of strontium are synthesized through sol-gel method accompanied by high-temperature calcination. With the increase of Sr content, the crystal structure of samples changes from perovskite to spinel phase that promote both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) property. As a cathode catalyst for Li-O 2 battery, LaSrNiO nanoparticles show a capacity performance of 9000 mAh·g−1 and significantly enhanced cyclability. The improved battery performance with Sr-doped nanoparticles can be ascribed to the high surface area of Sr-doped LaSrNiO nanoparticles combined with mixed spinel and perovskite phased structure which facilitate specific capacity and OER performance obviously. This research work is believed to shed light on a new thought to boost the performance of Li-O 2 battery. • LaSrNiO are prepared via sol-gel way accompanied by high-temperature calcination. • LaSrNiO nanoparticles possess mixed perovskite and spinel phase for Sr doping. • Unique crystal structure of LaSrNiO effectively boost Li-O 2 battery performance. [ABSTRACT FROM AUTHOR]

Platinum nanoparticles (NPs) were photo-deposited on SnO 2 -C nanocomposites prepared by sol-gel method. Surface morphology of the prepared materials, examined by scanning electron microscopy (SEM) and transmission electron microscopy, confirmed selective deposition of Pt NPs on SnO 2 nanoclusters formed on carbon surface. X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) analysis, cyclic voltammetry (CV) and CO stripping experiments revealed modification of the electronic properties of the Pt NPs photo-deposited on the oxide-carbon composite in comparison to Pt/C prepared by the carbonyl chemical route. Rietveld refinement was employed to identify existing phases of catalysts and to determine the crystallite size. Micro-strain and intrinsic stacking fault increased and decreased, respectively, as a function of crystallite size. Pt loadings were determined by inductively coupled plasma mass spectrometry (ICP-MS). The oxygen reduction reaction (ORR) activity of the electrocatalysts was investigated in acid media using the rotating disk electrode (RDE) system. Accelerated durability test (ADT) results showed that photo-deposited Pt nanoparticles onto SnO 2 -C nanocomposite are more durable than those chemically deposited on carbon. • Pt/SnO 2 -C composite electrocatalysts were prepared by photo-deposition. • For comparison, platinum nanoparticles were chemically deposited on carbon. • Metal-support interaction was studied by physical and electrochemical characterization. • Pt/SnO 2 -C catalysts showed high oxygen reduction activity in acid media. • Durability of the Pt/SnO 2 -C catalyst was superior in comparison with Pt/C. [ABSTRACT FROM AUTHOR]

In this work, a glucose-derived carbon supported CrN composite is prepared by using a hydrothermal method and followed by a nitridating process. It is found that CrN nanoparticles in the composite are well-dispersed and separated by the carbon support. More importantly, the composite exhibits significantly enhanced oxygen reduction reaction activity than free-standing aggregated CrN nanoparticles, especially in acidic medium. The onset potential of the composite reaches 0.81 V in acidic medium, which is one of the highest values among the reported metal nitrides. The rotating ring disk electrode results indicate that the composite is more beneficial to O 2 dissociation than free-standing CrN nanoparticles. Results of X-ray photoelectron spectroscopy, O 2 temperature-programmed desorption and electrochemical impedance spectroscopy indicate that the significantly enhanced oxygen reduction reaction activity of the composite over free-standing CrN is derived not from the new formed active sites or enhanced oxygen adsorption but from the much enhanced electron transfer rate. This observation helps to understand the role of electron transfer rate playing in the oxygen reduction reaction activity of metal nitrides. Image 1 • Glucose-derived carbon supported well-dispersed CrN nanoparticles are prepared. • The ORR onset potential of the catalyst reaches 0.81 V in acidic medium. • The catalyst shows much enhanced ORR activity than aggregated CrN nanoparticles. • The catalyst is more beneficial to O 2 dissociation than aggregated CrN. • The much enhanced ORR activity is attributed to enhanced electron transfer rate. [ABSTRACT FROM AUTHOR]

In this study, top-down synthesis of sulfur-doped graphene nanosheets (SDGNs) by simple electrochemical exfoliation was explored as a means of producing metal-free electrocatalysts for oxygen reduction and oxygen evolution reactions (ORR and OER, respectively). In a typical procedure, graphite foils were used to obtain bulk quantities of SDGN catalysts in the presence of thiosulfate as a sulfur source. Highly stable colloidal dispersions of SDGNs were obtained by applying a voltage of 15 V at an optimized Na 2 S 2 O 3 :H 2 SO 4 molar ratio of 5 : 1 (denoted SDGN(5)). Physicochemical characterizations by Raman spectroscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy confirmed the existence of sulfur and its electronic/structural properties in graphene nanosheets. In alkaline media, SDGN(5)-modified electrodes were comparable or superior to pristine graphene and a benchmark commercial platinum-based electrodes in terms of stability, methanol tolerance, n values, and onset potential for ORR and OER. The specific capacitance (149.9 F g−1) of SDGN(5) supported its excellent ORR/OER performance and enhanced surface area. [ABSTRACT FROM AUTHOR]

Designing efficient and durable bifunctional oxygen catalyst to replace expensive Pt catalysts in oxygen reduction reaction and oxygen evolution reaction is crucial for various energy conversion devices, such as metal-air batteries and fuel cells. Although various nanocarbon/metal oxides have been developed, their catalytic efficiencies remain unsatisfactory; moreover, bi-functionality and the issue of long-term durability have remained elusive goals. Herein, we report the self-assembly of interconnected nickel-cobaltite nanocrystals on nitrogen-doped graphene via hydrothermal synthesis. The Co3+ sites, the key radicals for bifunctional oxygen reduction and evolution reactions. Well-dispersed nitrogen-doped graphene serve as a platform for anchoring the interconnected nickel-cobaltite nanocrystals and improve the conductivity to maintain a high saturation current in oxygen reduction and low overpotential in evolution reaction, similar to Pt/C. Lifetimes as long as 200 h for oxygen reduction and 300 h for oxygen evolution are demonstrated with negligible degradations. The present approach paves the way for the rational design of various Gr-metal oxide hybrids for numerous applications. Image 1 • Interconnected i -NiCo 2 O 4 grown on nitrogen-doped graphene via self-assembly strategy. • The interconnected nanostructure prevented the migration of nanoparticles. • The electrocatalytic activity was evaluated in oxygen reduction/evolution reactions. • The hybrid exhibited high catalytic activity and long term durability. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) on an electrode is a multi-step process that involves both H 2 O and H 2 O 2 as final products, and the mechanism focusing on the productions of them has yet to be elucidated. In this study, simplifying the multi-step process of ORR by means of rate-limiting step (RLS) led to a H 2 O 2 -mediated pathway model. This model accounts for the productions of H 2 O and H 2 O 2 by the H 2 O 2 -mediated strategy existing in 2 × 2e pathway. The model links the overall reaction with RLS and serves to establish the electrochemical kinetic equations of sub-processes. A tending degree (R H2O2) quantifying the "tendency" toward H 2 O and H 2 O 2 was proposed. Finally, a mathematic approach based on the H 2 O 2 -mediated strategy are formed and well account for two common ORR behaviors: i) H 2 O 2 is inevitably produced on most of the ORR catalysts, including Pt-based catalysts, and ii) the tendency is regulable from external factors rather than merely determined by the intrinsic properties of catalysts. Furthermore, this model is fully validated by the kinetic simulations of the ORR behaviors in the rotating ring-disk electrode (RRDE) system. This study opens a way to advance the ORR applications by regulating the tendency, and may facilitate the comprehensive understanding of ORR mechanism. [ABSTRACT FROM AUTHOR]

Development of abundant and cost-effective electrocatalysts for hydrogen evolution reaction (HER) has gained momentum in recent years. In spite of being one of the largest class of materials, very few metal oxides have shown the propensity for HER in acidic medium. Herein, we report V 10 O 24.nH 2 O nanofibers as an excellent electrocatalyst material for HER for the first time. We show that V 10 O 24.nH 2 O nanostructures with a mixed V5+/V4+ oxidation state and a jute-fiber like morphology having a layered disposition and large interlayer spacing of 1.3 nm characterized by interlayer water molecules, can act as an excellent HER electrocatalyst in acidic medium. It required a low overpotential of 118 mV reaching to −10 mA cm−2 current density and at 600 mV overpotential reached a current density of −405 mA cm−2. It showed excellent durability retaining ca. 90% of its initial activity even after cycling for more than 11 h. Mechanism of the HER electrocatalysis was investigated by Tafel analysis that revealed typical Volmer-Heyrovsky mechanism for the HER with an excellent exchange current density of 1.62 mA cm−2. The vanadium oxide catalyst was also explored as oxygen reduction reaction electrocatalyst for application in alkaline fuel-cells. • Layered V 10 O 24.nH 2 O nanofibers with large interlamellar spacings of ∼ 1.3 nm was synthesized via hydrothermal method. • HER activity was achieved in acidic medium, one of the rare instances where metal oxides have been reported for the same. • Requires low overpotentials of -126 and 600 mV to achieve current densities of -10 mAcm-2 and -425 mAcm-2, respectively. • Nanofibers were also active for oxygen reduction reaction in alkaline medium with onset potential of ∼ 0.67 V vs RHE. [ABSTRACT FROM AUTHOR]

Functional low-cost catalysts derived from earth abundant materials are vitally important for enabling mass implementation of renewable energy conversion systems, such as fuel cells and metal-air batteries. Herein, we report the activation of earth-abundant coal to realize very active and stable catalysts for the oxygen reduction reaction (ORR) through oxidative pretreatment followed by thermal treatment under ammonia forming self-doped heteroatoms and defects. The coal thermally pretreated in air at 350 °C for 30 min followed by treatment in ammonia for 2 h presented very good electrocatalytic ORR activity with onset potential of 0.978 V, half-wave potential of 0.871 V, Tafel slope of 57 mV dec−1, and predominant 4-electron reduction of O 2 to OH−. The influence of the preoxidation step prior to ammonia treatment on the properties of the coal-derived carbon and hence the ORR has been specifically studied. The optimized catalyst also displayed stable performance during the ORR in 0.1 M NaOH for a test period of 35 h and exhibited excellent tolerance to methanol. The preoxidation step facilitates elimination of aliphatic and amorphous carbon, condensation of aromatic structures and the formation of initial pore structures, and subsequent removal of unstable heteroatoms from aromatic carbon rings to form surface and edge defects as potential active sites for promoting the ORR. Using pristine coal as raw material to produce functional ORR catalysts will be of great importance for real applications. [ABSTRACT FROM AUTHOR]

Microbial fuel cell (MFC) technology has been widely experimented nowadays, as it is a promising clean energy technology, which can harvest bioelectricity while simultaneously treating wastewater. Platinum (Pt), a precious transition metal, has long been regarded as a superior catalyst material for oxygen reduction reaction (ORR) at the cathode of the MFCs, however the high cost associated with it clutch it back for field scale applications. In this study, Co 3 O 4 or Fe 3 O 4 was blended with synthetically prepared conductive ink to act as microporous layer to explore its efficacy as an ORR catalyst. Applicability of these catalysts on cathode was investigated in dual chambered aqueous cathode MFCs and the performance was compared with MFC without any cathode catalyst, MFC with only conductive ink and another MFC with Pt as benchmark ORR catalyst. X-Ray diffraction, Fourier transform infrared spectra, Raman and field emission scanning electron microscope analysis were done to characterize the prepared catalysts. Cathode containing Co 3 O 4 with conductive ink demonstrated higher reduction current (- 30 mA) than cathode having Pt and conductive ink with Fe 3 O 4 (- 9 mA each) during cyclic voltammetry analysis. MFCs having cathodes printed with conductive ink containing Co 3 O 4 and Fe 3 O 4 exhibited a maximum volumetric power density of 6.62 W m−3 and 5.06 W m−3, respectively, which were much higher than the one without any catalyst (2.95 W m−3). Similarly, coulombic efficiency (CE) of 22.3%, 17.1% and 11.2% was observed in MFCs having cathode with conductive ink containing Co 3 O 4 or Fe 3 O 4 and without any catalysts, respectively. Moreover, more than 90% chemical oxygen demand removal efficiency was observed for MFCs having cathode with conductive ink containing Co 3 O 4 or Fe 3 O 4. Importantly, the performance obtained from MFC with conductive ink blended Co 3 O 4 was found superior compared to MFC having Pt as cathode catalyst, where later produced power density of 6.13 W m−3 and CE of 21.1%. Hence, it can be concluded that Co 3 O 4 can be used as an alternative to expensive platinum for efficient ORR in MFCs to make this technology effective for field scale application. • Conductive ink printed Co 3 O 4 or Fe 3 O 4 cathode catalyst improve MFC performance. • MFC with conductive ink printed Co 3 O 4 cathode gave higher power density than Pt. • 22% Coulombs recovery observed with conductive ink printed Co 3 O 4 as cathode catalyst. • Electrochemical analysis showed higher redox activity of the fabricated materials. [ABSTRACT FROM AUTHOR]

• Simple synthesis of MnO2 nanostructures by hydrothermal method • Comparative ORR study for different nanostructured-MnO2 modifying Vulcan XC-72 • Highest H2O2 electrogeneration using 1% α-MnO2/Vulcan XC-72 (402 mg L-1) The electrochemical performances of the α-MnO 2 /Vulcan XC-72 and δ-MnO 2 /Vulcan XC-72 nanostructures in hydrogen peroxide (H 2 O 2) electrosynthesis were compared herein. Both materials were synthesized by a simple hydrothermal route. Their structures and morphologies were analyzed by SEM, HRTEM, XPS, Raman Scattering and XRD, and their ORR electrochemical properties and H 2 O 2 electrosynthesis efficacies were investigated in alkaline NaOH solutions applying the rotating ring-disk electrode (RRDE) technique. Gas diffusion electrode (GDE) setups in acid media aiming at H 2 O 2 formation were also performed. The 3% δ-MnO 2 /C and 1% α-MnO 2 /C electrocatalysts were more efficient and selective than pure Vulcan XC-72 through the ORR 2-electron pathway in the RRDE essays. Concerning H 2 O 2 electrogeneration using GDE, the 1% α-MnO 2 /C electrocatalyst displayed better activity, with peroxide accumulation of 402.6 mg/L at -1.9 V (vs Ag/AgCl) after 120 min, 48 % higher than pure Vulcan XC-72 GDE. These results can be ascribed to a synergistic effect between α-MnO 2 and Vulcan XC-72, as well as oxygen functional acid species improvement, increasing electrocatalytic surface hydrophilicity and enhancing H 2 O 2 electrosynthesis. [Display omitted] [ABSTRACT FROM AUTHOR]

Being attractive among metal-air batteries due to its high theoretical energy density and voltage, aprotic magnesium-oxygen system is still much less studied than alkali metal-oxygen ones. Here we report a comparative study of Mg–O 2 cells with carbon-based cathode in various aprotic solvents: DMSO, diglyme, MeCN and tetramethylene sulfone. We found that the main discharge product in DMSO-based electrolyte is amorphous MgO 2 , with noticeable concentration of sulfur-containing byproducts being revealed. Upon partial electrode passivation, one-electron oxygen reduction to superoxide is observed on cycling voltammograms, and MgO 2 is predominantly formed by chemical disproportionation of superoxide. As for recharge, it was shown that the depassivation of the electrode proceeds along with the electrolyte (or carbon electrode) oxidation in any electrolyte solvents. In electrolyte solvents except DMSO the discharge capacity is quite limited due to metallic Mg anode issues. The addition of chloride ions to DMSO- and diglyme-based electrolyte solution increases the discharge voltage without affecting the charge process. The results contribute to the further development of electrolyte composition for rechargeable MgO 2 electrochemical system. [ABSTRACT FROM AUTHOR]