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Search for a Platinum metal-free catalyst for Proton Exchange Membrane Fuel Cells (PEMFCs) is a concern to scientists as the Pt-catalyzed electrode comprises about 45% of the entire fuel cell stack cost. Due to layered structure, Two-dimensional (2D) MoS2 nanostructured materials have recently drawn attention as effective catalysts for oxygen reduction reaction (ORR). The 1T-phase of MoS2 (1T-MoS2) has higher electronic conductivity than the 2H-phase (2H-MoS2); high surface area 1T-MoS2 can have high electrocatalytic activity towards PEFFCs. Here, we report hydrothermally synthesized 2H-MoS2 and solvothermally synthesized mixed 1T/2H-MoS2 phases as a catalyst for ORR in PEM Fuel Cells. Owing to the high BET-specific surface area, hybrid 1T/2H-MoS2 showed better ORR activity than 2H-MoS2. The limiting current density of the 1T/2H-MoS2 hybrid structure is ‒7.1 mA cm−2 compared to Pt/C (‒8.2 mA cm−2) at 1600 rpm. The Tafel slope values of 2H-MoS2, 1T/2H-MoS2, and Pt/C are 92.7 mV dec−1, 57.5 mV dec−1, and 39.3 mV dec−1, respectively. The electron transferred during ORR are 3.8 and 1.8, respectively, for 1T/2H-MoS2 and 2H-MoS2 (in 0.1 M KOH) ; suggesting less formation of undesirable peroxide formation than 2H-MoS2. The 1T/2H-MoS2 displays better electrochemical durability compared to 2H-MoS2 (after 2000 CV cycles). [ABSTRACT FROM AUTHOR]

Highlights: A novel A/B-sites co-substitution strategy was introduced to enhance the performance and durability of Ruddlesden–Popper perovskite Sr3Fe2O7−δ (SF)-based air electrodes for reversible protonic ceramic cells (RePCCs). Simultaneous Sr-deficiency and Nb-substitution in SF result in Sr2.8Fe1.8Nb0.2O7−δ (D-SFN), offering improved structural stability under RePCC conditions by suppressing the formation of Sr3Fe2(OH)12 phase. The introduction of Sr-deficiency enhances oxygen vacancy concentration in D-SFN, promoting efficient oxygen transport within the material and contributing to excellent activity in RePCCs. Reversible protonic ceramic cells (RePCCs) hold promise for efficient energy storage, but their practicality is hindered by a lack of high-performance air electrode materials. Ruddlesden–Popper perovskite Sr3Fe2O7−δ (SF) exhibits superior proton uptake and rapid ionic conduction, boosting activity. However, excessive proton uptake during RePCC operation degrades SF's crystal structure, impacting durability. This study introduces a novel A/B-sites co-substitution strategy for modifying air electrodes, incorporating Sr-deficiency and Nb-substitution to create Sr2.8Fe1.8Nb0.2O7−δ (D-SFN). Nb stabilizes SF's crystal, curbing excessive phase formation, and Sr-deficiency boosts oxygen vacancy concentration, optimizing oxygen transport. The D-SFN electrode demonstrates outstanding activity and durability, achieving a peak power density of 596 mW cm−2 in fuel cell mode and a current density of − 1.19 A cm−2 in electrolysis mode at 1.3 V, 650 °C, with excellent cycling durability. This approach holds the potential for advancing robust and efficient air electrodes in RePCCs for renewable energy storage. [ABSTRACT FROM AUTHOR]

Anaerobic digestion (AD) was initially evaluated as a potential preprocessing method for preparing biomass-based carbon electrocatalysts in this study. The AD pretreatment succeeded in the structural depolymerization and nitrogen enrichment of Hybrid Pennisetum, which provided favorable conditions to achieve efficient and homogeneous nitrogen introduction due to microorganism community enrichment and provided a porous structure by degradation of the biodegradable components. The resulted biochar exhibited improved physiochemical properties including higher specific surface areas, nitrogen content and graphitization degree than that obtained from pyrolyzing raw biomass. These improvements were positively correlated with the AD time and showed to have enhanced the performance in oxygen reduction reaction and practical microbial fuel cell applications. Amongst the investigated samples, the obtained biochar pretreated by AD for 15 days exhibited the most excellent performance with an onset potential of 0.17 V (VS. saturated calomel electrode) and the maximal power density of 543.2 mW cm−2 assembled in microbial fuel cells. This study suggested applying AD as a new biological pretreatment in the preparation of biomass-based electrocatalysts, and provided a unique pathway for fabricating high-performance biochar-based catalysts by structure optimization and N-containing active sites construction via gentle biological method, thereby providing a cost-effective method to fabricate metal-free catalysts for oxygen reduction reaction. Highlights: Anaerobic digestion pretreatment was conducted to assist electrocatalyst preparation. The biological pretreatment succeeded in carbohydrates decomposition and nitrogen enrichment. Pretreatment derived biochar significantly increased the ORR activity and microbial fuel cell performance. [ABSTRACT FROM AUTHOR]

Highlights: The advancement and current status of dual-atom catalysts are reported. The synergistic effects exhibited by recent dual-atom catalysts in mechanistic studies are classified and summarized. Challenges and prospects of dual-atom catalysts in synthesis, characterization, applications, and theory are discussed. The exploration of sustainable energy utilization requires the implementation of advanced electrochemical devices for efficient energy conversion and storage, which are enabled by the usage of cost-effective, high-performance electrocatalysts. Currently, heterogeneous atomically dispersed catalysts are considered as potential candidates for a wide range of applications. Compared to conventional catalysts, atomically dispersed metal atoms in carbon-based catalysts have more unsaturated coordination sites, quantum size effect, and strong metal–support interactions, resulting in exceptional catalytic activity. Of these, dual-atomic catalysts (DACs) have attracted extensive attention due to the additional synergistic effect between two adjacent metal atoms. DACs have the advantages of full active site exposure, high selectivity, theoretical 100% atom utilization, and the ability to break the scaling relationship of adsorption free energy on active sites. In this review, we summarize recent research advancement of DACs, which includes (1) the comprehensive understanding of the synergy between atomic pairs; (2) the synthesis of DACs; (3) characterization methods, especially aberration-corrected scanning transmission electron microscopy and synchrotron spectroscopy; and (4) electrochemical energy-related applications. The last part focuses on great potential for the electrochemical catalysis of energy-related small molecules, such as oxygen reduction reaction, CO2 reduction reaction, hydrogen evolution reaction, and N2 reduction reaction. The future research challenges and opportunities are also raised in prospective section. [ABSTRACT FROM AUTHOR]

Copyright of Carbon Research is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

CaO is demonstrated as a synergistic electro-catalyst for oxygen reduction reaction on strontium-doped lanthanum ferrite (La0.8Sr0.2FeO3−δ, LSF) cathodes for intermediate-temperature solid oxide fuel cells based on yttria-stabilized zirconia (YSZ) electrolytes. With 3.01 wt% CaO, the interfacial polarization resistance at 750 °C is reduced from 0.83 to 0.42 Ω cm2 for LSF-SDC (samaria-doped ceria) composite electrodes on the YSZ electrolytes. With 3.2 wt% CaO, the peak power density at 800 °C is increased from 0.45 to 0.58 Wcm−2 for anode supported single cells consisting of Ni-YSZ anodes, YSZ electrolytes, and LSF-SDC cathodes. The CaO particles can greatly enhance the kinetics of oxygen reduction reaction on LSF such as improving the oxygen surface exchange coefficient at 750 °C from 1.9 × 10−5 to 54×10−5 cm s−1 as demonstrated by the electrochemical conductivity relaxation measurement. Specifically, CaO particles infiltrated to the LSF electrodes reduce the interfacial polarization resistance associated with the low-frequency response, which is often attributed to the surface reaction steps of the cathode reaction. [ABSTRACT FROM AUTHOR]

Highlights: Analyzed the function of internal polarization field in Ni2P/FeP2 via hydroxyl spillover effect. From theoretical design to experimental verification, to optimize adsorption energy of oxygen intermediates on Ni active site, and further boost the xygen evolution reaction process. A hydroxyl spillover effect driven by internal polarization field in Ni2P/FeP2 can be amplified in low concentration alkaline electrolyte environment, and facilitate the application in anion exchange membrane water electrolyzer systems. The formation of multiple oxygen intermediates supporting efficient oxygen evolution reaction (OER) are affinitive with hydroxyl adsorption. However, ability of the catalyst to capture hydroxyl and maintain the continuous supply at active sits remains a tremendous challenge. Herein, an affordable Ni2P/FeP2 heterostructure is presented to form the internal polarization field (IPF), arising hydroxyl spillover (HOSo) during OER. Facilitated by IPF, the oriented HOSo from FeP2 to Ni2P can activate the Ni site with a new hydroxyl transmission channel and build the optimized reaction path of oxygen intermediates for lower adsorption energy, boosting the OER activity (242 mV vs. RHE at 100 mA cm–2) for least 100 h. More interestingly, for the anion exchange membrane water electrolyzer (AEMWE) with low concentration electrolyte, the advantage of HOSo effect is significantly amplified, delivering 1 A cm–2 at a low cell voltage of 1.88 V with excellent stability for over 50 h. [ABSTRACT FROM AUTHOR]

In this paper, we present a study on the synthesis and electrochemical characterization of nitrogen-doped reduced graphene aerogel (NrGA) prepared through the hydrothermal reduction of graphene oxide (GO) suspension with urea as a nitrogen dopant source. Five samples (rGA, NrGA08, NrGA16, NrGA32, NrGA48) with varying concentrations of urea were prepared to investigate the effect of urea concentration on electrochemical performance. All samples were characterized using XRD, FT-IR, Raman, BET, FESEM, and XPS. The specific surface area of the samples ranged from 110 to 344 m2/g, with the highest value observed for NrGA48. Raman spectroscopy showed the generation of disorder in the structure with the insertion of nitrogen atoms. The electrochemical performance of the sample has been investigated through linear sweep voltammetry, cyclic voltammetry, chronoamperometry, and RDE. The NrGA32 sample exhibited superior electrochemical performance compared to the other samples, and was therefore chosen as the optimized N-doped sample to investigate the effect of cobalt phthalocyanine (CoPC) as a redox mediator. The addition of CoPC significantly improved the electrochemical properties of NrGA32, increasing the electron transfer number from 3.5 to 3.85, enhancing the oxygen reduction current, and shifting the onset potential from 0.480 to 0.700 V vs. SHE. [ABSTRACT FROM AUTHOR]

The preparation of platinum-free electrocatalysts with ideal oxygen reduction reaction (ORR) activity is of great significance for cost-effective fuel cells. Herein, we synthesize a series of Pd-based (PdFe, PdCo, PdNi, and Pd) nanowires (PdM NWs). Their diameters are about 10 nm. And the lengths are up to even micrometers. The mass activity of the series of Pd-based catalysts followed the descending order: PdNi NWs/C > commercial Pt/C > PdCo NWs/C > PdFe NWs/C > pure Pd NWs/C. The optimal half-wave (E1/2) of PdNi NWs/C (839 mV) is positive shift 138 and 25 mV compared with pure Pd NWs/C (701 mV) and commercial Pt/C (814 mV), respectively. The mass activity (MA) of PdNi NWs/C only dropped 28% after 10,000 potential cycles between 0.6 and 1.1 V versus RHE in acid medium. This work provides a promising and reliable strategy to synthesize high performance Pd-based electrocatalyst, which is promising alternative to expensive Pt-based electrocatalysts for fuel cells. TOC: We prepared bimetallic PdNi nanowires, which ORR mass activity higher than pure Pd nanowires and commercial Pt/C in acidic medium. [ABSTRACT FROM AUTHOR]

Recently, transition metal nitrides (TMNs) are a suitable candidate for electrode materials due to their high conductivity, large surface area, electronic structure, and interesting mechanical properties. However, the activity of oxygen reduction reaction (ORR) is too poor to meet the performance and cost requirements in zinc–air batteries. Doping with the other foreign atoms can optimize the structure and performance of TMNs. In this paper, the d-band center of titanium nitride (TiN) was regulated by introducing Cr ions into the lattice, which can lower the energy barrier of the rate determination step (RDS). Moreover, the degree of graphitization of carbon materials and the surface area can be optimized directly by doping amount of chromium into the lattice of TiN. Benefiting from that, the Ti0.95Cr0.05N/NC/C exhibited an onset potential as high as 0.854 V, an ultimate current density of 4.1 mA·cm−2, remarkable stability and durability. The zinc–air battery based with Ti0.95Cr0.05N/NC/C has 1.25 V open-circuit voltage, a 760.26 mAh·g−1 specific capacity, and excellent long-time discharge performance. This work provides a reliable way to develop stable and efficient binary transition metal nitride electrocatalysts. [ABSTRACT FROM AUTHOR]

Expanding the application scenarios of wood-derived biochar guided by the conversion of traditional energy to new energy shows great promise as a field. As thrilling energy conversion apparatus, zinc-air batteries (ZABs) require cathode catalysts with high oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities and stability. Herein, two-dimensional nickel-iron hydroxide nanosheets were creatively assembled in N-doped wood-derived biochar (NiFe-LDH@NC) by an in-situ growth method. The categorized porous organization in wood-derived biochar facilitates the rapid seepage of electrolytes and rapid diffusion of reaction gases. The unique interfacial structure of biochar and NiFe-LDH accelerates electron transfer during oxygen electrocatalysis, and endows NiFe-LDH@NC with first-class catalytic activity and durability for ORR and OER. The ZAB derived from NiFe-LDH@NC showed elevated discharge productivity and cycle endurance, making it promising for viable applications. This work provided a convenient way for the conversion of wood-derived biochar to high-value added electrocatalysts. Article Highlights: Heteroatom-doped wood-derived biochar was assisted in situ growth of NiFe-LDH. NiFe-LDH@NC exhibited excellent bifunctional activity and stability toward ORR/OER. The ZAB achieved a peak power density of 123 mW cm−2 and a cycling stability of 270 h. [ABSTRACT FROM AUTHOR]

Although porphyry systems like metallo-phthalocynine are recognized as promising molecular models for electrocatalytic oxygen reduction reaction (ORR), their poor durability and methanol tolerance are still challenges and need improvement before being considered for practical applications. Herein, we successfully designed and constructed a Fe-phthalocyanine-derived highly conjugated 2D covalent organic framework (2D FePc-COF), using octa-amino-Fe-phthalocyanine (OA-FePc) and cyclohexanone as precursors. The prepared 2D FePc-COF was characterized via multiple analytic techniques. The electrochemical studies indicated that prepared 2D FePc-COF was far more superior to OA-FePc and 20% Pt/C, displaying anodic shift of 100 and 50 mV (vs RHE) in formal potential, respectively. Moreover, this catalyst also demonstrated excellent methanol tolerance and durability (over 10,000 CV cycles). Theoretical investigations revealed that due to extended conjugation and elimination of electron donating groups (-NH2), the shifting of dz2-orbital (Fe) energy took nearer to π*-orbital (O2), allowing optimum coupling of both the orbitals, thereby enhancing 4e− ORR. This work demonstrates the art of molecular design, aiming at improving catalytic activity of macrocyclic molecular systems towards ORR. [ABSTRACT FROM AUTHOR]

Reduction in solid oxide fuel cells operating temperature to intermediate range (500–700°C) causes significant increase in the electrode polarization, especially at cathode due to high activation energy for oxygen reduction reaction (ORR). In fact, electrochemical performance of cathode significantly depends on the synthesis routes owing to the change in microstructures. PrBaCo2O5+δ double-perovskite cathode is synthesized using four different synthesis routes viz. combustion, sol–gel, mechanochemical alloying and solid-state reaction to obtain desired microstructure in view of optimum electrochemical performance. PrBaCo2O5+δ prepared with different routes crystalizes into tetragonal structure with crystallite size in the range of 48–64 nm. Maximum electronic conductivity (σdc = 178 S cm–1 at 700°C) and minimum polarization resistance (Rp = 0.112 Ω cm2 at 700°C) along with minimum Ea (0.51 eV) for combustion synthesized PrBaCo2O5+δ are attributed to its minimum effective particle size (382 nm), grain size and optimum porosity. Nanocrystallites not only improve sinterability and mechanical strength of cathode but also promotes (large, disordered surface area) chemical and electrochemical processes in it, thereby improve overall electrode performance. Defect equilibria are proposed to understand dependence of σdc and Rp on P O 2 , temperature and crystallite size. The electrochemical performance of PrBaCo2O5+δ shows that the charge transfer during ORR is the rate-limiting step. Thus, PrBaCo2O5+δ prepared using combustion can be a potential cathode for IT-OFC applications. [ABSTRACT FROM AUTHOR]

In this work, carbon-supported Pt-Fe catalysts (Pt-Fe/C) have been synthesized to determine the electrochemical activity toward oxygen reduction reaction (ORR). Compared to the Pt/C catalyst, the Pt-Fe/C catalyst showed around 23% less area-specific activity but 8.6% more mass activity. These findings suggest the possibility to develop a catalyst that is both more active and cost-efficient than platinum. Furthermore, Pt-Fe/C catalyst was successfully compared as a cost-effective catalyst alternative to the Pt/C catalyst. [ABSTRACT FROM AUTHOR]

We report the development of a novel electrocatalyst composed of nanoarchitectured spinel cobalt manganese oxide and graphene for the oxygen reduction reaction (ORR). A combination of co-precipitation and hydrothermal methods achieved the unique nanoarchitecture of the electrocatalyst. The formation of CoMn2O4 electrocatalyst was confirmed by X-ray diffraction, transmission electron microscopy, and other spectroscopic and microscopic techniques. In addition to synthesizing CoxOy and MnxOy as control electrocatalysts, we created a physical mixture of CoMn2O4 and graphene to investigate the impact of their interface on electrocatalytic activity. Our findings indicate that CoMn2O4/graphene exhibits improved ORR activity, stability, and methanol tolerance in an alkaline medium. This enhancement can be attributed to the synergistic effect and strong interface interaction between CoMn2O4 and graphene. This study demonstrates the potential of the proposed electrocatalyst as a cost-effective and eco-friendly alternative for oxygen reduction in fuel cells applications. [ABSTRACT FROM AUTHOR]

The development of new energy storage and conversion pathways has gradually freed people from dependence on oil, and improving conversion efficiency and safety is still the mainstream trend in the development of new energy sources, and electrode catalysts have become crucial in solving these problems. At present, precious metal catalysts have good performance, but the scarcity of resources and the high price limit commercialization. Therefore, it is very important to develop a catalyst for commercialization. In this paper, the Pt nanoparticles were successfully loaded on the mesoporous FeCo2O4 nanosheet catalyst by the sodium borohydride (NaBH4) reduction method. The formation of the Pt-O bond results in covalent coupling between Pt and FeCo2O4. The increase in defect sites also facilitates improved catalytic activity. According to the test results, the ORR process is mainly carried out through the "4-electron reaction" pathway, and the main product is water, and the Tafel slope of Pt-FeCo2O4 (-73 mV dec−1) is smaller than that of Pt/C (-84 mV dec−1) and FeCo2O4 (-76 mV dec−1). The stability of Pt-FeCo2O4 to ORR (After 12 h, only 15.5% current density loss) is significantly higher than that of commercial Pt/C. Meanwhile, in the OER process, Pt-FeCo2O4 (28.1 mA cm−2) has a higher current density than RuO2 (24.4 mA cm−2) and FeCo2O4 (15.1 mA cm−2). Therefore, Pt-FeCo2O4 can be used as a bifunctional catalyst to accelerate the ORR and OER processes, which has important theoretical research significance and commercial value. [ABSTRACT FROM AUTHOR]

The preparation of porous carbon from biomass flour as high-performance electrocatalysts for oxygen reduction reaction (ORR) was reported in this paper. The fast and vigorous pyrolysis of flour was induced in the presence of magnesium nitrate, by which MgO nanoparticles were introduced as nano-template to create numerous nanopores and to increase the specific surface area (SSA). The pore structure, SSA and elemental dopant were influenced by the ratio of biomass to magnesium nitrate and calcination temperature. A highly hierarchical micro-meso-macroporous carbon, which was calcined at 1000 °C and had a high SSA of 1880 m2 g−1, exhibited the best ORR performance in terms of fast ORR kinetic, superior stability and excellent methanol tolerance. [ABSTRACT FROM AUTHOR]

Highlights: JUC-610-nanosheet exhibits highly efficient oxygen reduction reaction (ORR) catalytic activity in alkaline electrolyte with half-wave potential of 0.72 V versus reversible hydrogen electrode, which is one of the best covalent organic frameworks (COF)-based ORR electrocatalysts reported so far. It has been confirmed by experiments and density functional theory calculations that the abundant electrophilic structure in Q3CTP-COFs induces a highly density of carbon active sites, and the unique bilayer stacking facilitates the exposure of active carbon sites and accelerates the mass diffusion during ORR. JUC-610-nanosheet can also serve as a promising cathode for Zn-air batteries (power density of 156 mW cm–2 at 300 mA cm–2), which promotes the development of metal-free carbon-based electrocatalysts. Metal-free carbon-based materials are considered as promising oxygen reduction reaction (ORR) electrocatalysts for clean energy conversion, and their highly dense and exposed carbon active sites are crucial for efficient ORR. In this work, two unique quasi-three-dimensional cyclotriphosphazene-based covalent organic frameworks (Q3CTP-COFs) and their nanosheets were successfully synthesized and applied as ORR electrocatalysts. The abundant electrophilic structure in Q3CTP-COFs induces a high density of carbon active sites, and the unique bilayer stacking of [6 + 3] imine-linked backbone facilitates the exposure of active carbon sites and accelerates mass diffusion during ORR. In particular, bulk Q3CTP-COFs can be easily exfoliated into thin COF nanosheets (NSs) due to the weak interlayer π–π interactions. Q3CTP-COF NSs exhibit highly efficient ORR catalytic activity (half-wave potential of 0.72 V vs. RHE in alkaline electrolyte), which is one of the best COF-based ORR electrocatalysts reported so far. Furthermore, Q3CTP-COF NSs can serve as a promising cathode for Zn-air batteries (delivered power density of 156 mW cm–2 at 300 mA cm–2). This judicious design and accurate synthesis of such COFs with highly dense and exposed active sites and their nanosheets will promote the development of metal-free carbon-based electrocatalysts. [ABSTRACT FROM AUTHOR]

Cathodic electrical stimulation has previously been studied for both the augmentation of bone healing as well as the treatment of implant associated infections. One of the proposed mechanisms of both of these effects is the electrochemical generation of hydrogen peroxide during the oxygen reduction reaction. Titanium and 316L stainless steel are commonly used as implants and surgical hardware in orthopedic applications. The oxygen reduction reaction has been shown to be complex on passivated metal electrodes such as these. Therefore, the exact potential ranges of H2O2 generation on these materials in physiologically relevant media are not fully characterized. This study employed Rotating Ring-Disk Electrode techniques as well as Scanning Electrochemical Microscopy methods to characterize the electrochemical generation of H2O2 on titanium and 316L stainless steel. [ABSTRACT FROM AUTHOR]

The rational construction and preparation of efficient, stable, and economic electrocatalysts for the oxygen reduction reaction (ORR) are necessary for fuel cells. In this work, we fabricated a porous carbon skeleton structure consisting of bimetallic organic framework (BMMOF)-derived N-doped microspheres linked with graphene oxide (GO) conducting network (denoted as UA-Co/RSC@NGF, where "UA" stands for ultrasound-assisted, "RSC" stands for resin microspheres, and "NGF" stands for N-doped graphene framework) as an efficient ORR catalyst by an ultrasound-assisted and one-step pyrolysis method. In this configuration, benefiting from the support of carbon microspheres and the strong synergistic coupling with GO, the structure of UA-Co/RSC@NGF is stabilized, and the large specific surface area enhances the density of active sites. With UA-Co/RSC@NGF as the catalyst, significant ORR properties were achieved with a high half-wave potential (E1/2, 0.90 V), an onset potential (Eonset, 1.03 V), and a large limited current density (5.37 mA cm−2). The durability and methanol resistance of UA-Co/RSC@NGF in alkaline media outperform commercially available Pt/C. This study may open a pathway for rationally designing multidimensional composite-structured carbon-based ORR catalysts for energy-related applications. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Highlights: Fundamental principles for designing highly efficient two-electron oxygen reduction reaction catalysts are briefly reviewed. Strategies to integrate the components into an efficient device for hydrogen peroxide production are discussed. The challenges and perspectives for catalyst and cell design are discussed. Electrochemical synthesis of H2O2 via a selective two-electron oxygen reduction reaction has emerged as an attractive alternative to the current energy-consuming anthraquinone process. Herein, the progress on electrocatalysts for H2O2 generation, including noble metal, transition metal-based, and carbon-based materials, is summarized. At first, the design strategies employed to obtain electrocatalysts with high electroactivity and high selectivity are highlighted. Then, the critical roles of the geometry of the electrodes and the type of reactor in striking a balance to boost the H2O2 selectivity and reaction rate are systematically discussed. After that, a potential strategy to combine the complementary properties of the catalysts and the reactor for optimal selectivity and overall yield is illustrated. Finally, the remaining challenges and promising opportunities for high-efficient H2O2 electrochemical production are highlighted for future studies. [ABSTRACT FROM AUTHOR]

Perovskite-type Nd0.75Ba0.25Co0.8Fe0.2O3-δ (NBCF25) was prepared via solid-state synthesis method at 1300 °C in air. Powder X-ray diffraction showed the formation of a single-phase orthorhombic phase in the Pnma space group. It showed minor reactivity with Sr and Mg-co-doped lanthanum gallate (LSGM) when sintered with 30 wt.% LSGM at 1050 °C. 4-probe DC chronopotentiometry measurements were performed on the sintered sample pellets and showed a maximum conductivity of 674 S/cm at 700 °C. 2-probe AC electrochemical impedance spectroscopy measurements were performed on LSGM pellets from 650 to 800 °C to investigate the oxygen reduction property of NBCF25 using a composite slurry (70 wt.% NBCF and 30 wt.% LSGM). It showed the lowest area-specific resistance of 0.07 Ω cm2 at 800 °C in air. Impedance spectroscopy genetic programming was used to understand the oxygen reduction reaction. [ABSTRACT FROM AUTHOR]

The development of high-efficiency oxygen reduction reaction (ORR) catalysts is crucial to the advancement of fuel cell technology. Herein, a flexible and free-standing carbon fiber membrane immobilized with atomically dispersed Fe-Nx@NC catalyst is synthesized via electrospinning methodology using suitable complexing agents. A major advantage of the newly designed intertwined fibers is that a highly open structure with abundant nanopores increases gas transportation, electrolyte infiltration, and electron transfer and exposes a high concentration of FeNx sites embedded in the carbon matrix. And Fe4N nanoparticles are generated during pyrolysis and dispersed on carbon fibers upon pyrolysis treatment at 800 °C and co-exist with numerous formed Fe–Nx moieties in the carbon matrix, being evidenced by using X-ray absorption and photoelectron spectroscopy. These factors contribute to excellent ORR activities of FeNx sites. As an ORR catalysts, the as-synthesized Fe-Nx@NC catalyst delivered a more positive half-wave potential of 0.90 V compared to commercial Pt/C. Based on the analyses of the scanning electron microscopy (SEM), the transmission electron microscopy (TEM), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy, combined with the density functional theory (DFT) calculations, the generation of FeNx active sites and the formation of the four-coordinate structure of Fe because of the existence of nitrogen-containing complexes were explained, and the catalyst also shows the higher onset potential and half-wave potential in electrochemical tests. [ABSTRACT FROM AUTHOR]

We have constructed N-piperidinyl-substituted trioxotriangulene (TOT) surface as the catalyst for both the oxygen reduction reaction (ORR) pathways, i.e., 2e− and 4e−. Density functional theory (DFT) is used to study the 2e− and 4e− ORR at two active sites, the O site (oxygen) and N site (nitrogen) in the N-piperidinyl-substituted TOT surface. Reactants and intermediates adsorbate are chemisorbed while the product is physisorbed. The free energy values demonstrate that the O site favors strong catalysis for 2e− and 4e− pathways. In the 4e− reduction pathway, associative mechanism is exothermic and highly feasible. The overpotential values are low at 0.88 V for the O-active site in the associative mechanism in the 4e− pathway. All the results identify the new catalyst, N-pipeTOT surface a potential subject of study for fuel cell applications. [ABSTRACT FROM AUTHOR]

Biomass-derived carbon materials have been widely studied as oxygen reduction reaction (ORR) catalysts in recent years, and most directly carbonized materials are still inferior to commercial 20% Pt/C in ORR performance. By ball-milling the carbon powder carbonized by yuba, the interior of carbon particles was exposed, which showed that N content inside carbon particles is higher than that on the surface. Then ultrasonication was employed to refresh the surface of the as-obtained carbon particles to increase C-N-active sites to improve their ORR performance. As a result, the as-treated carbon material was comparable to 20% Pt/C as ORR catalyst in all the key ORR activity parameters (only 7 mV and 16 mV negative shift on onset and half-wave potential, respectively, and 0.28 mA cm−2 at −0.5 V versus Hg/HgO larger in limiting current density). Moreover, the ORR durability and the CO resistance of YUC-850 outperformed that of 20% Pt/C. The detailed experiments indicate that ultrasonication treatment can efficiently exfoliate the small raised material portions of low N content from regular particles to expose more refreshed surface with high N content to improve ORR activity. The subsequent centrifugation collection can remove the small particles to inhibit active site coverage and particle coarsening in service, which leads to further improvement in ORR activity and durability. Ultrasonication of another biomass-derived carbon material also showed significantly improved ORR performance. In conclusion, the application of ultrasonication treatment to biomass-derived carbon materials is proposed to fully promote their ORR activity and durability. The superior ORR performance of the treated carbon materials in this paper also indicates that biomass-derived carbon materials indeed have the potential to serve as redox catalysts in the future. [ABSTRACT FROM AUTHOR]

Highlights: The strong interaction between Ti3C2Sx and FeN4 species induces the central metal Fe(II) in FeN4 species with intermediate spin state transferred to high spin state, in which the latter is favorable to initiate the reduction of oxygen. This strong interaction induces a remarkable Fe 3d electron delocalization with d band center upshift, boosting oxygen-containing groups adsorption on FeN4 species and oxygen reduction reaction kinetics. The resulting FeN4–Ti3C2Sx with FeN4 moieties in high spin state exhibits high half-wave potential of 0.89 V vs. RHE and high limiting current density of 6.5 mA cm−2, enabling wearable zinc–air battery showing a good discharge performance with a maximum power density of 133.6 mW cm−2. Transition metal–nitrogen–carbon materials (M–N–Cs), particularly Fe–N–Cs, have been found to be electroactive for accelerating oxygen reduction reaction (ORR) kinetics. Although substantial efforts have been devoted to design Fe–N–Cs with increased active species content, surface area, and electronic conductivity, their performance is still far from satisfactory. Hitherto, there is limited research about regulation on the electronic spin states of Fe centers for Fe–N–Cs electrocatalysts to improve their catalytic performance. Here, we introduce Ti3C2 MXene with sulfur terminals to regulate the electronic configuration of FeN4 species and dramatically enhance catalytic activity toward ORR. The MXene with sulfur terminals induce the spin-state transition of FeN4 species and Fe 3d electron delocalization with d band center upshift, enabling the Fe(II) ions to bind oxygen in the end-on adsorption mode favorable to initiate the reduction of oxygen and boosting oxygen-containing groups adsorption on FeN4 species and ORR kinetics. The resulting FeN4–Ti3C2Sx exhibits comparable catalytic performance to those of commercial Pt-C. The developed wearable ZABs using FeN4–Ti3C2Sx also exhibit fast kinetics and excellent stability. This study confirms that regulation of the electronic structure of active species via coupling with their support can be a major contributor to enhance their catalytic activity. [ABSTRACT FROM AUTHOR]

Non-precious transition metal oxides demonstrate significant potential as cost-effective alternatives for noble metals electrocatalysts. The perovskite-type oxides with the general ABO3 chemical formula of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) can be used as non-precious metal catalysts for the oxygen reduction reaction (ORR). However, the catalytic activity toward the ORR of the LSCF prepared by the conventional methods can be further improved. Herein, the spray pyrolysis process is employed to prepare the LSCF, exhibiting high ORR activity. The characterization results indicated that the as-prepared LSCF was rich in surface edges and oxygen vacancy on the surface of particles, which could be favorable for ORR. Preparing edge-enriched perovskite electrocatalyst toward oxygen reduction reaction with spray pyrolysis technology. [ABSTRACT FROM AUTHOR]

The development of high-performance electrocatalysts is critical for the widespread applications of the sustainable energy technologies. In this context, single-atom catalysts (SACs) with isolated metal sites have attracted more attention because of their maximum atom utilization and remarkable electrocatalytic performance. However, the high surface energy often results in a low loading of the single metal atoms, limiting their practical applications. Herein, we give an up-to-date review on the progress for the SACs. The research progress of noble metal SACs, transition metal SACs, single-atom alloy SACs, and double metal SACs is summarized. The advantages and disadvantages of synthesis strategies including wet chemistry, atomic layer deposition, and high-temperature pyrolysis are discussed. We also propose some new research direction to obtain the high-performance SACs. It is expected to realize widely applications of SACs. [ABSTRACT FROM AUTHOR]

It has been found that composites based on Co,N,S-doped carbon and Co9S8 can act as catalysts for the hydrogenation of quinoline and its monomethyl derivatives providing the formation of 1,2,3,4-tetrahydroquinolines with 75-99% yields. The high efficiency of these systems is caused first of all with the presence of Co-Nx sites in their composition, which are formed as a result of the pyrolysis of cobalt salts and poly-5-aminoindole. The use of highly dispersed Vulcan XC72R carbon black as a component of the reaction mixture during the composite catalyst preparation by the pyrolysis contributes to a greater extent to the formation of active Co-Nx sites in them, compared to graphene oxide or in the case when a carbon component is not added. [ABSTRACT FROM AUTHOR]

The weak interaction between common carbon support and Pt nanoparticles results in low efficiency for the oxygen reduction reaction (ORR) with high overpotentials, which greatly limits the practical application of proton exchange membrane fuel cells. Employing strong metal–support interaction (SMSI) is a promising method for tuning the electronic structure of Pt to boost the ORR, accompanied by rapid improvement in durability. Herein, titanium carbide (TiC) was grown on the surface of carbon black by the sol–gel method coupled with high-temperature treatment (denoted as TiC-C). Based on the SMSI that occurred between TiC and Pt, the obtained Pt/TiC-C catalyst exhibits higher mass ORR activity, which is twice that of the commercial Pt/C-JM under the same conditions. In addition, the Pt/TiC-C exhibits superior durability relative to the Pt/C-JM by preventing the aggregation and dissolution of Pt nanoparticles during the ORR process. [ABSTRACT FROM AUTHOR]

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Highlights: A comprehensive discussion of monitoring the structure evolutions of catalysts during ORR via multiple in-situ techniques to identify the active sites is presented. The extensive applications of in-situ techniques in elucidating the oxygen reduction reaction (ORR) mechanisms/pathways are reviewed. The challenges and recommendations of current in-situ techniques for monitoring the various dynamic evolutions in ORR are pointed out. Electrocatalytic oxygen reduction reaction (ORR) is one of the most important reactions in electrochemical energy technologies such as fuel cells and metal–O2/air batteries, etc. However, the essential catalysts to overcome its slow reaction kinetic always undergo a complex dynamic evolution in the actual catalytic process, and the concomitant intermediates and catalytic products also occur continuous conversion and reconstruction. This makes them difficult to be accurately captured, making the identification of ORR active sites and the elucidation of ORR mechanisms difficult. Thus, it is necessary to use extensive in-situ characterization techniques to proceed the real-time monitoring of the catalyst structure and the evolution state of intermediates and products during ORR. This work reviews the major advances in the use of various in-situ techniques to characterize the catalytic processes of various catalysts. Specifically, the catalyst structure evolutions revealed directly by in-situ techniques are systematically summarized, such as phase, valence, electronic transfer, coordination, and spin states varies. In-situ revelation of intermediate adsorption/desorption behavior, and the real-time monitoring of the product nucleation, growth, and reconstruction evolution are equally emphasized in the discussion. Other interference factors, as well as in-situ signal assignment with the aid of theoretical calculations, are also covered. Finally, some major challenges and prospects of in-situ techniques for future catalysts research in the ORR process are proposed. [ABSTRACT FROM AUTHOR]

Highlights: A novel method is developed to prepare bifunctional oxygen electrocatalysts composed of Co nanoparticles and highly dispersed Fe loaded on N-doped carbon substrates by virtues of metal-organic frameworks and two different doping processes. The designed catalysts show comparable performance with commercial catalysts. Meanwhile, rechargeable Zn-air batteries with prepared catalysts demonstrate high peak power density and good cycling stability. The performance promotion originates from the synergy between Co nanoparticles and highly dispersed Fe, porous structures, large specific areas, and distinct three-dimensional carbon networks. Searching for cheap, efficient, and stable oxygen electrocatalysts is vital to promote the practical performance of Zn-air batteries with high theoretic energy density. Herein, a series of Co nanoparticles and highly dispersed Fe loaded on N-doped porous carbon substrates are prepared through a “double-solvent” method with in situ doped metal-organic frameworks as precursors. The optimized catalysts exhibit excellent performance for oxygen reduction and evolution reaction. Furthermore, rechargeable Zn-air batteries with designed catalysts demonstrate higher peak power density and better cycling stability than those with commercial Pt/C+RuO2. According to structure characterizations and electrochemical tests, the interaction of Co nanoparticles and highly dispersed Fe contributes to the superior performance for oxygen electrocatalysis. In addition, large specific surface areas, porous structures and interconnected three-dimensional carbon networks also play important roles in improving oxygen electrocatalysis. This work provides inspiration for rational design of advanced oxygen electrocatalysts and paves a way for the practical application of rechargeable Zn-air batteries. [ABSTRACT FROM AUTHOR]

Highlights: Synthesis of high-entropy perovskite oxide for air electrode in reversible proton ceramic electrochemical cells. Triple-conducting high-entropy air electrodes exhibit excellent structural stability and oxygen catalytic activity. The peak power density and current density of the cell with high-entropy air electrode in the fuel cell and electrolysis modes are 1.21 W cm−2 and − 1.95 A cm−2 at 600 °C, respectively. Reversible proton ceramic electrochemical cell (R-PCEC) is regarded as the most promising energy conversion device, which can realize efficient mutual conversion of electrical and chemical energy and to solve the problem of large-scale energy storage. However, the development of robust electrodes with high catalytic activity is the main bottleneck for the commercialization of R-PCECs. Here, a novel type of high-entropy perovskite oxide consisting of six equimolar metals in the A-site, Pr1/6La1/6Nd1/6Ba1/6Sr1/6Ca1/6CoO3−δ (PLNBSCC), is reported as a high-performance bifunctional air electrode for R-PCEC. By harnessing the unique functionalities of multiple elements, high-entropy perovskite oxide can be anticipated to accelerate reaction rates in both fuel cell and electrolysis modes. Especially, an R-PCEC utilizing the PLNBSCC air electrode achieves exceptional electrochemical performances, demonstrating a peak power density of 1.21 W cm−2 for the fuel cell, while simultaneously obtaining an astonishing current density of − 1.95 A cm−2 at an electrolysis voltage of 1.3 V and a temperature of 600 °C. The significantly enhanced electrochemical performance and durability of the PLNBSCC air electrode is attributed mainly to the high electrons/ions conductivity, fast hydration reactivity and high configurational entropy. This research explores to a new avenue to develop optimally active and stable air electrodes for R-PCECs. [ABSTRACT FROM AUTHOR]

Oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) electrocatalyst activity may be regarded as a crucial indicator of expected performance in metal-air batteries, which are limited by the inadequate electrochemical activity and low conductivity of accessible materials. This disadvantage can be solved by the development of hierarchically structured three-dimensional (3D) carbon. Through carbonization method, we synthesize the bifunctional catalysts, Fe, P, N, and S multidoped porous graphene (FePNS-G) for use in rechargeable Zn–air batteries (ZABs). FePNS-G-2 indicates superior active site density for both the OER and ORR. Moreover, the FePNS-G-2 exhibits excellent long-term electrochemical stability for 10 h in both the OER and ORR. ZABs assembled for FePNS-G-2 shows a higher power density (168.3 mW cm−2) and a higher specific capacity (782.36 mA h g−1) than benchmark Pt/C + IrO2 electrocatalyst. The sturdy durability of FePNS-G-2 for OER and ORR leads to the charge–discharge cycle durability. The excellent electrocatalytic activity and steady cycling life of FePNS-G-2 examines the air cathode as an electrocatalyst in feasible ZAB applications. [ABSTRACT FROM AUTHOR]

Using cheap graphite powder as catalyst and polytetrafluoroethylene (PTFE) as binder, graphite/PTFE composite coating cathodes were fabricated for efficient electrochemical synthesis of hydrogen peroxide (H2O2) in a no-diaphragm electrolysis system. A series of experiments were conducted to examine the influence of different factors, such as cathode thickness, cathode area, solution pH and current density, on H2O2 electrogeneration. Adjusting the thickness and area of the cathode was demonstrated to be effective in optimizing the electrocatalytic properties in oxygen reduction reaction. Among the cathodes investigated, the cathode with the thickness of 0.75 mm and area of 16 cm2 achieved the highest H2O2 accumulation and current efficiency. The H2O2 accumulation reached 207.5 mg L−1 and current efficiency reached 34.1% in 180 min when the current density is 5 mA cm−2 and the initial pH is 3.0. The present work successfully develops a simple approach to enhance the H2O2 electrogeneration, as well as the corresponding current efficiency, through optimization of cathode geometric parameters and operation conditions. [ABSTRACT FROM AUTHOR]

Making a consistency with the objectives of circular economy, herein, waste pistachios shells were utilized for the development of hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) electrocatalysts which are the key bottleneck in the technological evolution of electrolyzers and fuel cells, respectively. As an alternative to scarce and expensive platinum-group-metal (PGM) electrocatalysts, metal nitrogen carbons (MNCs) are emerging as a promising candidate for both aforementioned electrocatalysis where iron and nickel are the metal of choice for ORR and HER, respectively. Therefore, FeNCs and NiNCs were fabricated utilizing inedible pistachio shells as a low-cost biosource of carbon. The steps involved in the fabrication of electrocatalyst were correlated with electrochemical performance in alkaline media. Encouraging onset potential of ~ 0.88 V vs RHE with a possibility of a 2 + 2 reaction pathway was observed in pyrolyzed and ball-milled FeNC. However, HF etching for template removal slightly affected the kinetics and eventually resulted in a relatively higher yield of peroxide. In parallel, the pyrolyzed NiNC demonstrated a lower HER overpotential of ~ 0.4 V vs RHE at − 10 mA cm−2. Nevertheless, acid washing adversely affected the HER performance and consequently, very high overpotential was witnessed. [ABSTRACT FROM AUTHOR]

The sluggish kinetics of oxygen reduction reaction (ORR) and the high cost of traditional Pt-based catalyst prompt us to develop highly efficient alternatives with low cost. In this paper, nitrogen-doped graphene (NG)-supported palladium (Pd) and cobalt (Co) catalysts were prepared by the improved Hummers methods assisted with metal ion adsorption and thermal reduction processes, and subsequently were used as electrocatalysts for ORR in alkaline solution. The X-ray diffraction analysis illustrated that the (111), (200), and (220) crystal planes of PdCo/NG shifted in the high-angle direction relative to Pd/NG, mainly due to the simultaneous loading of Pd and Co on NG. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) measurements further confirmed that metallic Pd and Co nanoparticles were simultaneously loaded on NG and uniformly distributed. The Pd and Co nanoparticles were 3–30 nm and 2–15 nm in size, respectively. In particular, unlike the Co nanoparticles encapsulated by several carbon layers in Co/NG, no carbon layers were detected outside of Co nanoparticles in PdCo/NG. This is probably due to the existence of Pd that prevents the carbon agglomeration around Co. Electrochemical measurements suggested that all catalysts manifested catalytic activity for ORR, and ORR catalyzed by them obeys the first-order reaction kinetics with respect to the concentration of O2 in the solution. The PdCo/NG has the most positive peak potential (−0.198 V versus Ag/AgCl) of oxygen reduction in the cyclic voltammetry (CV) curves and most positive onset potential (−0.056 V versus Ag/AgCl) in the linear sweep voltammetry (LSV) curves, illuminating its excellent ORR activity relative to the catalysts loaded with Pd or Co alone. The ORR catalyzed by metal-free NG mainly goes through a 2e− pathway, while a mixed 2e− and 4e− pathway dominated the ORR catalyzed by Pd/NG, Co/NG, and PdCo/NG. Compared with Pd/NG- and Co/NG-catalyzed ORR, the electron transfer number stabilized at 3.2 without fluctuation with the potential negative shift, and the Koutecký–Levich (K–L) plots have better linearity and parallelism for PdCo/NG. These indicated that ORR steps are more concise and stable on PdCo/NG than on other samples. Such conspicuous features of PdCo/NG are probably ascribed to the simultaneous loading of Pd and Co nanoparticles. In particular, replacing partial Pd with Co not only reduces the cost, but also improves the activity of the electrocatalysts. This work developed a bimetallic-supported catalyst with low cost and highlighted the feasibility of replacing partial Pd with Co supported on carbons as ORR electrocatalyst, laying the foundation for large-scale application of non-Pt catalysts. [ABSTRACT FROM AUTHOR]

The exploitation of highly sustainable, highly efficient catalysts toward oxygen reduction reaction to replace the precious Pt is a key issue for metal air batteries. In this report, sustainable pollen derived three-dimensional porous carbon/graphene composites with Zn and N doping are developed as non-precious catalyst toward oxygen reduction reaction. The prepared Zn and N doped porous carbon/graphene composites show a hierarchical porous structure, large specific area, and high N contents. As catalyst toward oxygen reduction reaction, the prepared sample with an optimized graphene content exhibits a half-wave potential ~ 0.90 V (versus reversible hydrogen electrode), and a limited current density of 5.5 mA cm−2 in alkaline electrolytes. Meanwhile, it manifests remarkable electrochemical stability and superior tolerance to methanol poisoning. It is found that Zn, N doping and introduction of graphene are key factors for the improved oxygen electrocatalytic capability because active sites and conductivity are strengthened. Moreover, the prepared sample also shows a good oxygen reduction activity in acid electrolyte. Density functional theory calculations demonstrate that Zn–N4 is the major and the most active site. On the basis of the excellent performance, the prepared composites with renewable biomass sources may have a good potential as a highly efficient and durable oxygen reduction electrocatalysts. [ABSTRACT FROM AUTHOR]

Single-metal-atom catalysts (SMACs) have garnered extensive attention for various electrocatalytic applications, owing to their maximum atom-utilization efficiency, tunable electronic structure, and remarkable catalytic performance. In particular, carbon-based SMACs exhibit optimal electrocatalytic activity for the oxygen reduction reaction (ORR) which is of paramount importance for several sustainable energy conversion and generation technologies, such as fuel cells and metal-air batteries. Despite continuous endeavors in developing various advanced carbon-based SMACs for electrocatalytic ORR, the rational regulation of coordination structure and thus the electronic structure of carbon-based SMACs remains challenging. In this review, we critically examine the role of coordination structure, including local coordination structure (i.e., metal atomic centers and the first coordination shell) and extended local coordination structure (i.e., the second and higher coordination shells), on the rational design of carbon-based SMACs for high-efficiency electrocatalytic ORR. Insights into the relevance between coordination structures and their intrinsic ORR activities are emphatically exemplified and discussed. Finally, we also propose the major challenges and future perspectives in the rational design of advanced carbon-based SMACs for electrocatalytic ORR. This review aims to emphasize the significance of coordination structure and deepen the insightful understanding of structure-performance relationships. [ABSTRACT FROM AUTHOR]

Combing the Mn metal–organic frameworks (MnMOFs) actives with rational carbon-matrix support is an effective way to develop high-performance non-noble metal catalysts in fuel cells. Herein, a novel non-Pt cathodic catalyst for oxygen reduction reaction (ORR), nitrogen co-doping into MnMOF nanoparticles wrapped in the reduced graphene oxide (N-MnMOF@rGO), was designed and successfully synthesized. The two-dimensional layered rGO can not only stabilize the structure of MnMOF, but also improve the overall conductivity of the composite catalyst. Meanwhile, the N doping could provide more active sites and improve the catalytic activity. Benefiting from the advantageous nanostructures featured with extremely high specific surface area, enriched catalytic active sites, and enhanced electronic transportation, the obtained N-MnMOF@rGO catalyst exhibits good catalytic performance. ORR test results show that the onset potential and half-wave potential are 0.88 V and 0.76 V, higher than those of the pure MnMOF, respectively. Furthermore, a small loss of current density after consecutive 10,000 cycles and a high electron transferred number of 4.3 are confirmed, indicating excellent stability and fast reaction kinetics. All these results demonstrate that the obtained N-MnMOF@rGO can be considered a highly potential non-Pt catalyst for practical ORR application in requirement of low cost, high catalytic behavior, and excellent stability. [ABSTRACT FROM AUTHOR]

To improve the oxygen reduction reaction (ORR) performance of biomass-derived carbon materials, N and P co-doped porous carbon ORR catalysts are synthesized by pyrolyzing the mixture containing different of yuba powder and metaphosphate (NaPO3) at 850 ℃ under N2 atmosphere. The as-prepared Y-850-5 contained 4.29 at% of N and 1.13 at% of P. The half-potential and the limiting diffusion current density of Y-850-5 are −0.153 V and −4.78 mA cm-2 @-0.5 V vs. Hg/HgO, respectively, which are improved by 6.5 % and 5.9 % compared to Y-850 (−0.163 V and −4.51 mA cm−2 @-0.5 V vs. Hg/HgO), respectively. DFT calculation indicate that the synergy of N and P co-dope resulted in changing the uniform distribution of electron cloud of carbon and lowering the ORR reaction energy barriers. The above results indicate that NaPO3 can be utilized as P resource to dope and improve the electrochemical performance biomass-derived porous carbon. [ABSTRACT FROM AUTHOR]

The sluggish nature of the cathodic oxygen reduction reaction (ORR), and the expensive price of the precious metal-based nanocatalysts are the biggest obstacles to the practical applications of cutting-edge technologies including metal–air batteries and fuel cells. Hence, it is crucial to engineering a scalable-production pathway for the fabrication of a high-performance ORR catalyst. Herein, it was aimed to boost the performance of the ORR in neutral media, especially for microbial fuel cells, by tailoring a biomass-derived ORR electrocatalyst. In this regard, with the approach of nanochemistry, which is concerned with the fabrication of building blocks that vary in size, surface, shape, and defect characteristics, iron- and nitrogen-doped activated carbon framework (Fe,N-AC) was derived from waste orange peels by a two-stage pathway comprising microwave-assisted chemical activation and the thermal annealing processes. The physicochemical characterizations confirmed the successful co-doping of iron and nitrogen atoms to the activated carbon skeleton with the hierarchically ordered porous structure. Thanks to the interdependent effects of metal and heteroatoms in the structure, as well as the enlarged specific surface area (1098 m2.g−1), Fe,N-AC catalyst offered a superior ORR activity thru the 4-electron transferring way (n = 3.969) with long-term stability (81.4% retention of initial current over the period of 7200 s). The half-wave potential was determined as 0.871 V by the introduction of iron and nitrogen to the nanoarchitecture, implying the boosting impact of the iron and nitrogen decoration. Moreover, the exceptional electrocatalytic activity of Fe,N-AC was validated by an onset potential of 0.951 V that was ca.16 mV smaller than that of Pt/C catalyst (0.967 V). The accelerated S2− poisoning test of Fe,N-AC catalyst was outperformed to Pt/C catalyst, thereby foreboding its practical utilization in MFCs. The current loss of Pt/C catalyst was determined almost five times that of Fe,N-AC catalyst at 5 mM S2− concentration. The findings paved the course for the engineering of the state-of-the-art low-cost nanocatalyst by converting agricultural biomasses to a multi-functional advanced material to be employed in sustainable energy conversion systems. [ABSTRACT FROM AUTHOR]

Cobalt- and nitrogen-doped carbon nanotube-grafted flower- and leaf-like hierarchical porous carbon materials (Co,N/FLC@CNT) are prepared by growth of zeolitic imidazolate framework-67 (ZIF-67) on flower- and leaf-like zinc-ZIF (FL-Zn-ZIF) followed by thermal treatment without additional carbon source. This hierarchically porous structure can expose active sites efficiently and is also favorable for electrolyte permeation and O2 diffusion. Furthermore, the self-generation of CNTs can improve electron conduction. Co,N/FLC@CNT has high contents of pydinic- and graphitic-N and large electrochemical active surface area (463 cm2). The Co,N/FLC@CNT presents excellent ORR activity in terms of high limiting current density (5.6 mA cm−2) and half-wave potential (0.82 V), which is almost the same as commercial Pt/C. The H2O2 yield of Co,N/FLC@CNT for ORR is 11.3%, which is close to that of Pt/C (8.0%). The ORR on Co,N/FLC@CNT proceeds via 4e− path. Co,N/FLC@CNT presents better stability and methanol-tolerant ability than Pt/C. [ABSTRACT FROM AUTHOR]

N-Doped carbon electrocatalysts are a promising alternative to precious metal catalysts to promote oxygen reduction reaction (ORR). However, it remains a challenge to design the desired active sites on carbon skeletons in a controllable manner for ORR. Herein, we developed a facile approach based on oxygen-mediated solvothermal radical reaction (OSRR) for preparation of N-doped carbon electrocatalysts with a pre-designed active site and modulated catalytic activity for ORR. In the OSRR, 2-methylimidazole reacted with Co and Mn salts to form an active site precursor (MnCo-MIm) in N-methyl-2-pyrrolidone (NMP) at room temperature. Then, the reaction temperature increased to 140 °C under an oxygen atmosphere to generate NMP radicals, followed by their polymerization with the pre-formed MnCo-MIm to produce Mn-coupled Co nanoparticle-embedded N-doped carbon framework (MnCo-NCF). The MnCo-NCF showed uniform dispersion of nitrogen atoms and Mn-doped Co nanoparticles on the carbon skeleton with micropores and mesopores. The MnCo-NCF exhibited higher electrocatalytic activity for ORR than did a Co nanoparticle only-incorporated carbon framework due to the improved charge transfer from the Mn-doped Co nanoparticles to the carbon skeleton. In addition, the Zn–air battery assembled with MnCo-NCF had superior performance and durability to the battery using commercial Pt/C. This facile approach can be extended for designing carbon electrocatalysts with desired active sites to promote specific reactions. [ABSTRACT FROM AUTHOR]

Ce0.8Sm0.2O1.9 oxygen-ion conductor was infiltrated into the backbone of pre-prepared porous La1.8Sr0.2NiO4+δ electrode to enhance the electrocatalytic properties of the electrode for oxygen reduction reaction. The phase structure, microstructure, and electrocatalytic properties of the infiltrated electrodes were investigated in comparison with the pristine La1.8Sr0.2NiO4+δ electrode. The Ce0.8Sm0.2O1.9 infiltrated into the porous electrode backbone appeared as nano-sized particles deposited on La1.8Sr0.2NiO4+δ grains. The primary steps of the electrode reaction were facilitated to varying extents with the assistance of oxygen vacancies in the Ce0.8Sm0.2O1.9. As a result, the overall reaction kinetics of the infiltrated electrodes was accelerated. The oxygen vacancy-assisted acceleration effect was leveled off at a Ce0.8Sm0.2O1.9 loading of around 10 vol%. The leveling-off behavior was explained with respect to the microstructural evolution of the electrodes with increasing Ce0.8Sm0.2O1.9 loading. The 10 vol% Ce0.8Sm0.2O1.9 infiltrated electrode achieved appreciably improved electrocatalytic properties. Compared with the pristine La1.8Sr0.2NiO4+δ electrode, the polarization resistance (~0.25 Ω cm2) and overpotential (~53 mV at 200 mA cm−2) of the infiltrated electrode at 800 °C were reduced by ~40% and ~45%, respectively, while the exchange current density (~190 mA cm−2) was enhanced by ~66%. [ABSTRACT FROM AUTHOR]

Designing an efficient ORR electrocatalyst with superior methanol tolerance is crucial to fabricate direct methanol fuel cells (DMFC). In this regard, herein, Pt islands at Pd on carbon nanoparticles (Pd100-xPtx/C) was synthesized by combining the chemical reduction and galvanic replacement method, where Ag was used as a sacrificial element. The galvanic replacement of Ag by Pt in Pd100-xPtx/C was revealed from the absorption spectra with the absence of Ag's surface plasmon resonance (SPR) peak. XRD patterns endorse the formation of Pt@Pd/C and nanoscale crystallites. The photographic images of TEM demonstrate the formation of Pt islands at Pd on carbon matrix. The XPS spectra corroborate the metallic state of Pt and Pd in Pt20@Pd80/C. The optimum composition of Pt20-decorated Pd80 on carbon shows enhanced oxygen reduction reaction (ORR) in an acidic media. Moreover, Pt20-decorated Pd80 on carbon electrocatalyst exhibits low activation energy of 27.6 KJ mol-1 and superior tolerance towards methanol oxidation even at higher concentrations (20 M), signposting it as a promising ORR electrocatalyst for DMFC. [ABSTRACT FROM AUTHOR]

Among rechargeable batteries, metal-air batteries have attracted considerable attention because of their high theoretical specific energy, environmentally friendly, and low-cost. Oxygen reduction reaction (ORR) of electrocatalyst is considered to be a key reaction during discharge process of cathode, determining metal-air batteries performance. However, ORR electrocatalysts still face the key challenges of unsatisfactory electrocatalytic kinetics and complex preparation process that limits their wide applications. Herein, the research progresses of sustainable carbon-based ORR electrocatalysts are reviewed. We introduce the functional design approaches for performance improvement of carbon-based ORR electrocatalysts, including construction of pore structure, activation, and heteroatom doping. Abundant and inexpensive animal metabolites, plant, and microorganism are reviewed as raw material for obtaining high-performance ORR electrocatalysts. Furthermore, research directions of sustainable carbon-based ORR electrocatalysts are proposed. [ABSTRACT FROM AUTHOR]

Behavior of Pt/C catalysts obtained by the platinum deposition on standard and nitrogen-doped carbon supports with different microstructure has been studied in the oxygen electroreduction reaction in an acidic electrolyte. The catalysts based on the modified supports are characterized by a uniform spatial distribution of small-sized (1.5–2 nm) Pt nanoparticles over the surface of the supports, which results in high values of the electrochemically active surface area (110–130 m2 g− 1 (Pt)). The use of various stress testing protocols has shown that the Pt/C material based on the N-doped KetjenBlack EC DJ-600 possesses the highest mass activity and durability, which noticeably exceed the corresponding characteristics of the commercial HiSPEC3000 catalyst. [ABSTRACT FROM AUTHOR]