Search

The felicitous electrolyte with advance electrodes (cathode and anode) results in the development of an improved and efficacious battery/fuel cell. Perovskite based zinc‐air batteries with biological gel electrolyte prove to outperform the aqueous batteries. In this research, a zinc‐air battery was developed using a novel biocompatible electrolyte, Guar‐gum employing LaMnO3 (LMO) perovskite as a bi‐functional electro‐catalyst. The performance of the developed perovskite catalyst in guar‐gum electrolyte was obtained and compared with the performance of the material in both polymer gel (polyvinyl alcohol‐KOH) and aqueous medium. The bi‐functional catalyst shows enhanced catalytic activity, endurance and durability in alkaline medium with an open circuit voltage of 1.40 V, power density of 9.77 mW cm−2 at the current density of 11.12 mA cm−2 and a specific capacity of 2624 mAh g−1 comparatively competent with respect to the PVA‐based battery with the specific capacitance of 753 mAh g−1. Also, the rechargeable LMO zinc‐air battery exhibited excellent cycling stability at a current density of 10 mA cm−2. Thus, the results obtained proved the competent performance of the guar‐gum electrolyte compared to the previous developed polymer electrolyte. This is how the combination of LMO in the guar‐gum electrolyte is seen to be successful for commercial use in metal‐air batteries and fuel cells. [ABSTRACT FROM AUTHOR]

Hydrogen fuel cell technology is an essential component of a green economy. However, it is limited in practicality and affordability by the oxygen reduction reaction (ORR). Nanoscale silver particles have been proposed as a cost-effective solution to this problem. However, previous computational studies focused on clean and flat surfaces. High-index surfaces can be used to model active steps presented in nanoparticles. Here, we used the stable stepped Ag(322) surface as a model to understand the ORR performance of steps on Ag nanoparticles. Our density functional theory (DFT) results demonstrate a small dissociation energy barrier for O2 molecules on the Ag(322) surface, which can be ascribed to the existence of low-coordination number surface atoms. Consequently, the adsorption of OOH* led to the associative pathway becoming ineffective. Alternatively, the unusual dissociative mechanism is energetically favored on Ag(322) for ORR. Our findings reveal the importance of the coordination numbers of active sites for catalytic performance, which can further guide electrocatalysts' design. [ABSTRACT FROM AUTHOR]

Developing efficient Pt‐based alloy as oxygen reduction reaction (ORR) electrocatalysts is critical for practical applications of fuel cells. High‐temperature reduction technology can improve the alloy atoms ordering but inevitably accelerate metal sintering. Here, Pt–Ni nanoparticles (<5 nm) embedded into ordered mesoporous carbon (OMC) matrix are developed, and its confinement effect suppresses nanoparticles sintering up to 900 °C. After an elaborative dealloying process, the surface structure of Pt–Ni nanoparticles changes from a Ni‐rich to Pt‐rich layer (the thickness is about 0.15 nm). The optimized sample (PtNi3@OMC‐A) displays outstanding mass and specific activities of 2.11 A mgPt–1 and 3.23 mA cmPt–2, more than one order of magnitude higher than commercial Pt/C (20 wt%). PtNi3@OMC‐A also exhibits long‐term stability with a negligible activity loss after 10 000 potential cycles. Both experimental results and density functional theory calculations reveal that alloying effect as well as strain effect weaken Pt–O binding strength, thus resulting in an outstanding ORR activity. Furthermore, the high long‐term stability can be attributed to the confinement of OMC, inhibiting the detachment or agglomeration of the embedded alloy nanoparticles. [ABSTRACT FROM AUTHOR]

A new isolation protocol was recently reported for highly purified metallic Fullertubes D5h‐C90, D3d‐C96, and D5d‐C100, which exhibit unique electronic features. Here, we report the oxygen reduction electrocatalytic behavior of C60, C70 (spheroidal fullerenes), and C90, C96, and C100 (tubular fullerenes) using a combination of experimental and theoretical approaches. C96 (a metal‐free catalyst) displayed remarkable oxygen reduction reaction (ORR) activity, with an onset potential of 0.85 V and a halfway potential of 0.75 V, which are close to the state‐of‐the‐art Pt/C benchmark catalyst values. We achieved an excellent power density of 0.75 W cm−2 using C96 as a modified cathode in a proton‐exchange membrane fuel cell, comparable to other recently reported efficient metal‐free catalysts. Combined band structure (experimentally calculated) and free‐energy (DFT) investigations show that both favorable energy‐level alignment active catalytic sites on the carbon cage are responsible for the superior activity of C96. [ABSTRACT FROM AUTHOR]

TiO2-based mixed oxide–carbon composite supports have been suggested to provide enhanced stability for platinum (Pt) electrocatalysts in polymer electrolyte membrane (PEM) fuel cells. The addition of molybdenum (Mo) to the mixed oxide is known to increase the CO tolerance of the electrocatalyst. In this work Pt catalysts, supported on Ti1−xMoxO2–C composites with a 25/75 oxide/carbon mass ratio and prepared from different carbon materials (C: Vulcan XC-72, unmodified and functionalized Black Pearls 2000), were compared in the hydrogen oxidation reaction (HOR) and in the oxygen reduction reaction (ORR) with a commercial Pt/C reference catalyst in order to assess the influence of the support on the electrocatalytic behavior. Our aim was to perform electrochemical studies in preparation for fuel cell tests. The ORR kinetic parameters from the Koutecky–Levich plot suggested a four-electron transfer per oxygen molecule, resulting in H2O. The similarity between the Tafel slopes suggested the same reaction mechanism for electrocatalysts supported by these composites. The HOR activity of the composite-supported electrocatalysts was independent of the type of carbonaceous material. A noticeable difference in the stability of the catalysts appeared only after 5000 polarization cycles; the Black Pearl-containing sample showed the highest stability. [ABSTRACT FROM AUTHOR]

Developing economical electrocatalysts as alternatives to platinum for oxygen reduction reaction (ORR) to develop the applications of green energy devices like proton exchange membrane fuel cells (PEMFCs) is of paramount importance. In the current study, a different ratio of nitrogen-doped graphdiyne (GDY) with Fe single-site is reported to be more cost-effective and efficient for PEMFCs. The current study also demonstrates the design principle to improve the ORR activity associated with catalysts using Fe single-site with a greater Fe charge, which is controlled through the coordinated structure of the active center. Based on the simulation results, the formation of N 2 -doped GDY and N 2 -doepd Fe-GDY are more lucrative compared to the formation of Nx-doped GDY (x > 2) in terms of energy. O 2 molecules have a direct dissociation on the N 2 -doepd Fe-GDY via Eley-Rideal (ER) mechanism, which involves the formation of H 2 O by reacting with H+ from the electrolyte. Moreover, N 2 -doepd Fe-GDY exhibits better performance as an ORR catalyst in an acidic medium because of its low overpotential of 0.488 V. However, N 2 -doped GDY follows the OOH∗ formation pathway, showing a higher overpotential for ORR. Furthermore, in the structure under study, the thermodynamic favorability of ORR is observed since the reaction energies calculated at each reaction step are exothermic and the energy profile of all reaction steps are downhill. The results of the current work provide new insights into the construction of extremely efficient heterogeneous catalysts in electrochemical energy technologies. [Display omitted] • The catalytic activity of Fe-doped GDY has been theoretically explored in the ORR. • O 2 molecule can be directly dissociated on the N 2 -doped Fe-GDY. • It is reacting more favorable for the ER mechanism of OH∗ to convert into H 2 O. • The ORR reaction was found to be thermodynamically favorable in N 2 -doped Fe-GDY. [ABSTRACT FROM AUTHOR]

A non-precious metal electrocatalyst was obtained through the in-situ growth of iron phosphide (Fe 2 P) encapsulated by carbon nanotubes (CNTs) decorated with zeolitic imidazolate framework-8 (ZIF-8). Upon pyrolysis at a specific temperature, the ZIF-8/Fe 2 P@CNT catalyst exhibits high oxygen reduction reaction (ORR) ability and is close to the ideal electron transfer, which number is 3.99. The structure, high number of nitrogen-containing functional groups, and suitable surface properties of ZIF-8/Fe 2 P@CNT are critical for enhancing the ORR activity. ZIF-8/Fe 2 P@CNT exhibits a decay in electrocatalytic activity of 26 mV in the half-wave potential after 30 000 cycles, which is considerably superior to the decay of 123 mV for Pt/C after the same number of cycles. Therefore, ZIF-8/Fe 2 P@CNT exhibits excellent ORR activity and long-term stability and can be used as a fuel cell catalyst. [Display omitted] • ZIF-8 is grown in-situ on synthesized CNTs to form a ZIF-8/Fe 2 P@CNT catalyst. • Specific structure and unoccupied graphitic π∗ could catalyze the ORR activity. • ZIF-8/Fe 2 P@CNT exhibits excellent activity and long-term stability for fuel cell. [ABSTRACT FROM AUTHOR]

Polyazomethine (PAM) prepared from the polycondensation between p-phenylene diamine (PDA) and p-terephthalaldehyde (PTAl) via Schiff reaction can physically crosslink (complex) with Co ions. Co-complexed PAM (Co-PAM) in the form of gel is calcined to become a Co, N-co-doped carbonaceous matrix (Co-N-C), acting as cathode catalyst of an anion exchange membrane fuel cell (AEMFC). The obtained Co-N-C catalyst demonstrates a single-atom structure with active Co centers seen under the high-resolution transmission electron microscopy (HRTEM). The Co-N-C catalysts are also characterized by XRD, SEM, TEM, XPS, BET, and Raman spectroscopy. The Co-N-C catalysts demonstrate oxygen reduction reaction (ORR) activity in the KOH(aq) by expressing an onset potential of 1.19–1.37 V vs. RHE, a half wave potential of 0.70–0.92 V, a Tafel slope of 61–89 mV/dec., and number of exchange electrons of 2.48–3.79. Significant ORR peaks appear in the current–voltage (CV) polarization curves for the Co-N-C catalysts that experience two-stage calcination higher than 900 °C, followed by double acid leaching (CoNC-1000A-900A). The reduction current of CoNC-1000A-900A is comparable to that of commercial Pt-implanted carbon (Pt/C), and the max power density of the single cell using CoNC-1000A-900A as cathode catalyst reaches 275 mW cm−2. [ABSTRACT FROM AUTHOR]

Proton exchange membrane (PEM) fuel cells using Pt-based materials as electrocatalysts have achieved a decent performance, represented by the launched Toyota Mirai vehicle. The ideal PEM fuel cells consume stored pure hydrogen and air. However, SO2, as a primary air contaminant, may be fed along with air at the cathode, leading to Pt site deactivation. Therefore, it is important to improve the SO2 tolerance of catalysts for the stability of the oxygen reduction reaction (ORR). In this work, we develop the Pt/C-TiO2 catalyst against SO2 poisoning during ORR. Impressively, the hybrid Pt/C-TiO2 catalyst with 20 mass % TiO2 shows the best ORR and anti-toxic performance: the kinetic current density of ORR is 20.5% higher and the degradation rate after poisoning is 50% lower than Pt/C. The interaction between Pt and TiO2 as well as the abundant hydroxyl groups on the surface of TiO2 are both revealed to account for the accelerated removal of poisonous SO2 on Pt surfaces. [ABSTRACT FROM AUTHOR]

Transition metal (TM) single atomic catalysts (MSAC-N-C) derived from doped zeolite imidazolate frameworks (ZIF-8) are considered attractive oxygen reduction reaction (ORR) catalysts for fuel cells and metal-air batteries due to their advantages of high specific surface area, more active catalytic sites, adjustable pore size, and coordination topology features. This review provides an updated overview of the latest advances of MSAC-N-C catalysts derived from ZIF-8 precursors in ORR electrocatalysis. Particularly, some key challenges, including coordination environments regulation of catalysis center in MSAC-N-C, the active sites loading optimization and synergistic effects between TM nanoclusters/nanoparticles and the single atoms on MSAC-N-C catalysis activity, as well as their adaptability in various devices, are summarized for improving future development and application of MSAC-N-C catalysts. In addition, this review puts forward future research directions, making it play a better role in ORR catalysis for fuel cells and metal air batteries. [ABSTRACT FROM AUTHOR]

With the increasing consumption of the global energy demand, the electrochemical conversion and storage of new energy sources have drawn increasing attention in scientific research. As a promising energy conversion technology, fuel cells have attracted extensive attention in academia and industry due to their high energy conversion efficiency, environmental friendliness, high power density and wide range of fuels. Especially, oxygen reduction reaction (ORR) at the cathode is considered as an important electrode reaction in fuel cells. However, several factors, including slow kinetic process, extreme dependence on noble metal platinum, and rapid degradation of catalytic performance and durability after long-term operation, have severely restricted the large-scale promotion and application of these fuel cells commercialization. Therefore, the development of low-cost, highly active and stable catalysts is of great significance to promote the commercialization. Recently, Titanium nitride (TiN), as a highly durable support, has attracted extensive attention because of its superior properties of high conductivity, high melting point, high hardness, abrasion resistance and super anti-corrosion to acid and alkaline. When the advanced TiN material with favorable morphology and porous structure, high surface area and nanostructure is used as catalyst support, the electrocatalytic performance of Pt-based catalysts will be enhanced significantly due to the improved utilization of Pt, enhanced metal-support interactions, promoted mass/charge transfer as well as corrosion resistance. Interesting, TiN has also electronic properties similar to noble metal, and exhibits superior catalytic performance and durability toward ORR, thus obtaining widely attention in non-precious metal catalysts. Based on the above analysis, this review has summarized the current preparation method and synthesis mechanism of TiN materials, and elaborated the latest research progress including TiN, transition metal-doped TiN and its carbon-based composite materials as support or catalyst toward ORR. Based on the presented progress, we finally prospect the future application of TiN materials and directions for designing and developing practical fuel cell cathode catalysts. [ABSTRACT FROM AUTHOR]

Naturally abundant well-decomposed peat was used as a precursor for synthesizing several non-platinum group metal-type oxygen electrocatalysts. The materials were studied in an alkaline environment, where it was discovered that the oxygen evolution (OER) and the oxygen reduction (ORR) activity of the catalysts can be severely influenced by changing the parameters of the peat carbonization procedure. High OER activity was achieved with a minimally treated catalyst which seemed to be because of a Co-rich FeCo alloy species. In both rotating disc electrode and anion exchange membrane fuel cell experiments, the catalyst based on ZnCl 2 -activated peat-derived carbon showed superior ORR performance with a peak power density of 51 mW cm−2. It was found that the peak power densities of the catalysts correlated with several physical parameters. Above all, we demonstrate the possibility of fabricating advanced functional carbon materials for oxygen electrocatalysis from peat. [Display omitted] • Bifunctional platinum-free oxygen catalysts prepared from abundant decomposed peat. • Physical and catalytical properties can be tuned by modifying synthesis conditions. • Correlations between particle size properties and AEMFC performance established. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) plays a key role in the field of fuel cells. Efficient electrocatalysts for the ORR are important for fuel cells commercialization. Pt and its alloys are main active materials for ORR. However, their high cost and susceptibility to time-dependent drift hinders their applicability. Satisfactory catalytic activity of nanostructured transition metal phthalocyanine complexes (MPc) in ORR through the occurrence of molecular catalysis on the surface of MPc indicates their potential as a replacement material for precious-metal catalysts. Problems of MPc are analyzed on the basis of chemical structure and microstructure characteristics used in oxygen reduction catalysis, and the strategy for controlling the structure of MPc is proposed to improve the catalytic performance of ORR in this review. [ABSTRACT FROM AUTHOR]

To eliminate the concerns about fuel cell aroused by the scarcity of Pt and the sluggish kinetics of oxygen reduction reaction (ORR), shortening the pathway of mass transfer and optimizing the utilization of Pt are two effective ways. Herein, we report a facile strategy to efficiently anchor ultrafine Pt nanoparticles on ultrathin nanobowl‐shaped N‐doped carbon (Pt NP@BNC). Ultrathin layers of a two‐dimensional covalent organic framework (COF) were synthesized as the support via a hard‐template strategy and Pt precursors were homogeneously dispersed in the COF via a gas‐phase diffusion method. Then the composite was pyrolyzed and converted into ultrathin nanobowl‐shaped N‐doped carbon (ca. 6 nm) embedded with ultrafine Pt NPs (ca. 3.28±0.7 nm). Compared with the catalyst obtained from the bulk COF, Pt NP@BNC achieved significantly elevated activity towards ORR. This work may pave a new way for the design and synthesis of novel ORR catalysts with high efficiency. [ABSTRACT FROM AUTHOR]

Porous carbon materials are promising electrocatalysts for the oxygen reduction reaction (ORR). Their active sites, involving porosity and surface chemistry, are different from those of metal-doped carbons. The latter have been widely studied and are adapted to today's popular electrochemical devices, the rotating disk electrode being the most useful preliminary tool to evaluate their activity in ORR. However, porous carbon materials have been less explored, and experimental parameters need to be adjusted to achieve the best ORR performance. Therefore, in this study, the optimization of different key factors was investigated to evaluate their effect on the ORR performance of porous carbon electrocatalysts in alkaline medium. The parameters considered were: (i) the relevance of using RRDE or Koutecky-Levich equations for estimating the number of electrons transferred; (ii) the amount of ionomer (Nafion®); (iii) the carbon loading on the electrode; (iv) the carbon grinding method; and (v) the selection of the upper potential of ORR experiments. We conclude that an optimization of the experimental conditions should be done for each material studied, and we give important benchmarks for the appropriate evaluation of the catalytic activity in ORR of carbon-based catalysts. [Display omitted] [ABSTRACT FROM AUTHOR]

In the development of platinum group metal-free (PGM-free) catalysts like carbon-based catalysts for oxygen reduction reaction (ORR), one of the key factors is increasing active site density to achieve highly catalytic activity. This work proposes a facile method to effectively increase the ORR active site density by controlling the interfacial energy between the carbon support and heteroatomic precursor (FePc)-containing solution during solvothermal treatment. Decreasing the interfacial energy by purposefully choosing solvents with proper surface tension promotes the delivery of FePc into intrinsic pores of the carbon support and enhances Fe and N doping, resulting in an increase of ORR active site density by triple to 6.84 × 1018 sites g−1. The high density of active site helps to achieve higher onset potential (0.937 V vs. RHE) and half-wave potential (0.895 V) than the benchmark Pt/C in a same catalyst loading in 0.1 M KOH, as well as a higher power output (16.1 ± 0.3 mW cm−2) when used for air cathode catalyst in a membraneless direct formate fuel cell. These findings provide insights into synthesis of highly active carbon-based catalysts with high active site density and broaden the development for fuel cell application. [Display omitted] [ABSTRACT FROM AUTHOR]

The development of new synthetic methods for methanol-tolerant catalysts with improved performance is of fundamental importance for the commercialization of fuel cells. Herein, we reported a facile displacement reaction-assisted synthesis of graphene-supported sub-nanometer Pt/Bi catalysts (Pt/Bi/rGO). Bismuth (0) nanoparticles produced by NH3BH3 reduction can be further dissolved into the ethylene glycol, implying Bi(0) has a strong interaction with the hydroxyl group. That is the key interaction between Bi(0) and the functional group on the rGO to form the ultra-small Bi/rGO catalyst. Furthermore, Pt clusters are obtained by the displacement between Bi(0) and HPtCl4 and are directly anchored to the rGO surface. The as-synthesized Pt/Bi/rGO catalyst exhibits high oxygen reduction mass activity and high tolerance to methanol poisoning. In the presence of 0.5 mol/L CH3OH, the initial potential and activity of ORR were almost unchanged, which demonstrated great potential in the application of direct methanol fuel cells. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) is one of the fundamental reactions that occur on the cathode of fuel cells. The sluggish kinetics of ORR and the high cost of the conventionally used ORR electrocatalyst mandate extensive research towards the development of inexpensive, high‐performance and stable electrocatalysts. Various supported nanostructures of pristine noble metals and its alloys, transition metals/metal oxides (MOs), chalcogens/pnictogens doped metals/MOs, etc. have attracted great attention towards ORR in both acidic and alkaline electrolytes. This review primarily documents the recent advancements and challenges of supported nanomaterials with fascinating properties towards ORR. This study focuses on the use of carbon‐based materials as support. The significant factors like size, morphology, hetero‐atom doping, defects and interfaces (metal/metal, metal/oxide and metal/hydroxide) that can tailor ORR activity are portrayed elaborately. The electrochemical techniques and parameters that are adopted mainly during data collection and evaluation of ORR are also discussed. [ABSTRACT FROM AUTHOR]

Looking for non‐noble metal catalysts with low cost, high activity, and high stability to replace platinum in oxygen reduction reaction (ORR) has aroused great concern. According to previous studies, Fe‐Nx/C material is one of the most promising non‐noble metal catalysts for ORR. In this study, new Fe‐Nx/C material was synthesized by introducing CeO2 and Fe3O4 nanoparticles into a Fe‐Nx/C material derived from ZIF‐8 as precursors. The new material was called CeO2‐Fe3O4@Fe‐N/C catalyst and the activity of the catalyst was found to be significantly improved in 0.1 mol L−1 KOH. The half‐wave potential of CeO2‐Fe3O4@Fe‐N/C (0.892 V) is higher than that of Pt/C by 67 mV. In the stability test, the half‐wave potential of CeO2‐Fe3O4@Fe‐N/C was only reduced by 4 mV after 5,000 cycles. The high performance is attributed to the introduction of CeO2 and Fe3O4, which gives CeO2‐Fe3O4@Fe‐N/C enhanced electrocatalytic activity and long‐term stability. This approach makes CeO2‐Fe3O4@Fe‐N/C a promising candidate for cathode catalysts in renewable energy conversion devices. [ABSTRACT FROM AUTHOR]

The success of the next generation of anion-exchange membrane fuel cells (AEMFCs) depends on the development of active, reliable, and economical oxygen reduction reaction (ORR) catalysts. Here, we synthesize a series of ultra-low-cost metal-free ORR catalysts by doping a common pristine graphite precursor with chemically singular-type heteroatoms, namely I, S, N, or B, using single-step planetary ball milling technique. All doped-graphites show substantially enhanced ORR performance relative to the pristine (undoped) graphite. Among all the tested catalysts, N-graphite exhibited the highest ORR onset potential of 0.87 V vs. reversible hydrogen electrode. These results are supported by density functional theory calculations. The ORR catalysts also exhibit remarkable stability as evaluated through electrochemical tests. Most importantly, the AEMFCs prepared using these ultra-low-cost doped graphites deliver notable peak power densities with impressive voltage efficiencies, which further supports their efficacy in ORR catalysis and the broad implementation of this technology. [Display omitted] • Highly active metal-free doped-graphite catalysts for alkaline ORR are developed. • Comprehensive alkaline ORR investigation by structural and DFT modeling. • Remarkable catalyst stability is shown by electrochemical and corrosion tests. • High-performance anion-exchange membrane fuel cells using metal-free cathodes. • Ultra-low-cost ORR metal-free catalyst materials and fabrication process. [ABSTRACT FROM AUTHOR]

The cathode's oxygen reduction reaction (ORR) plays a crucial role in a variety of fuel cells. Developing affordable and efficient non-precious electrocatalysts for the ORR poses a major hurdle in the realm of electrochemical energy technologies. This work presents a transition metal-based catalyst, Fe-ONC, in which Fe is loaded in an oxygen-enriched nitrogen-doped carbon (NC) material. Oxygen enrichment of the catalyst was achieved by a pre-oxidation strategy. The XPS analysis reveals that Fe-ONC exhibits a higher abundance of oxidized species. The Fe of Fe-ONC exists in the form of Fe 3 O 4 particles and Fe-N x , respectively, which are uniformly distributed in the NC. The even spread of iron sites and the plentiful presence of oxygen-rich species are key factors in the superior ORR efficiency of Fe-ONC. Fe-ONC's half-wave potential (E 1/2) in an alkaline environment (0.1 M KOH) stands at 0.891 V, markedly surpassing the standard commercial Pt/C value (0.840 V). Additionally, Fe-ONC demonstrated enhanced longevity and resistance to ethanol in comparison to commercially available Pt/C. Fe-ONC's outstanding efficacy highlights its potential as an alternative to precious metal catalysts. The document outlines a plan for creating ORR catalytic materials that are sustainable, economical, and efficient. We propose to oxygenate the initial catalyst Fe-NC by pre-oxidation treatment, which increases the content of oxides and iron species with high oxidation valence states in the catalyst Fe-ONC, thus improving the catalyst activity and ORR performance. [Display omitted] • Fe-ONC is oxygenated by pre-oxidation treatment. • Oxygen-enriched Fe-N x sites boost ORR efficiency significantly. • Fe-ONC achieves a notable E 1/2 of 0.891 V in alkaline conditions. [ABSTRACT FROM AUTHOR]

Fe-N-C catalysts have developed into the most promising substitute for Pt-based precious metal catalysts toward cathodic oxygen reduction reaction (ORR) of fuel cells and Zn-air batteries. Hypercrosslinked polypyrrole microspheres coordinated with Fe (HCP-Py-Fe) were first prepared by condensation of pyrrole (Py) and dimethoxymethane (FDA) in the presence of FeCl 3 as both catalyst and Fe source, and then thermally activated with KOH during pyrolysis followed by acid leaching and heat-treatment, thus constructing hierarchically porous Fe-N-C microspheres (denoted as PPy/FDA-Fe y -HT2-x). The morphology and structural properties of the final synthesized PPy/FDA-Fe y -HT2-x could be tailored to a certain extent by controlling the adding quantities of KOH (x) in the initial solid mixture before pyrolysis and FeCl 3 (y) during condensation of Py and FDA. As a result, the PPy/FDA-Fe 0.4 -HT2–0.25 demonstrated the highest half-wave potential of 0.87 V vs. RHE, with a desired 4-electron transfer for ORR in alkaline medium, which is attributed to the hierarchically micro/mesoporous structure, high surface area and extremely low content of magnetic iron species. Remarkable methanol resistance and durability with only a loss of ∼4 mV in half-wave potential after 10000 potential cycles were obtained as well. The aqueous Zn-air battery (ZAB) fabricated with the PPy/FDA-Fe 0.4 -HT2–0.25 as cathode catalyst delivered a comparable discharge performance to that of the Pt/C-based ZAB but far superior cycling stability. This facile route is promising for large-scale production of Fe-N-C materials as cathodic electrocatalyst applied in practical energy conversion devices. [Display omitted] • Fe3+-catalyzed Friedel-Crafts reaction, pyrolysis with in situ activation was adopted. • Texture, Fe/N species percentages could be tuned by Fe3+-catalysis and KOH activation. • The Fe-N-C favored ORR in 4-e- way with a bit higher activity than that of the Pt/C. • The Fe-N-C microspheres showed better methanol resistance and stability than the Pt/C. • The ZAB assembled with Fe-N-C display superior discharge performance and durability. [ABSTRACT FROM AUTHOR]

Utilizing shrimp waste-derived Chitosan as biomass source, we developed metal-free nitrogen and sulfur-doped porous carbon (NSPC) with a high specific surface area of 609.53 m2/g as a remarkable electrocatalyst for oxygen reduction reaction (ORR), surpassing benchmark Pt/C with half-wave (0.8574 V) and onset (0.9573 V) potentials in alkaline (0.1 M KOH) media. Besides high electrocatalytic activity, NSPC-800 showed excellent methanol tolerance ability and significantly low hydrogen peroxide yields (H 2 O 2) of 5 % and 8 % in 0.1 M KOH and 0.5 M H 2 SO 4 , which is comparably lower than the previously reported chitosan based non-precious catalysts. Interestingly NSPC-800 displays robust stability in 0.1 M KOH electrolyte, improving the current retention rate from 89.17 % to 95.18 % over an increased operation period, evidencing its self-activating characteristics. This self-activating stability is also mirrored in 0.5 M H 2 SO 4 where both fresh and recycled (after 5000 CV cyles) NSPC-800 catalysts retained more than half of their initial current. Additionally, to identify the nature of the active sites, the ORR measurements were correlated with ex-situ spectroscopy for post-stability of fresh and recycled NSPC-800 catalysts revealed dynamic reconfiguration of nitrogen, sulfur, and oxygen active sites evidenced compared to the pre-stability elemental surface, indicating an adaptive response of the catalyst to the harsh operating environment. In the future, our biomass-derived NSPC-800 will pave the way to develop cost-effective and highly efficient catalysts from waste to energy devices promising a twin-goal approach, contributing to the circular economy and sustainable development goals. Schematic illustration of chitosan-derived nitrogen and sulfur-doped porous carbon (NSPC-800) and its application in fuel cells, associated contribution in sustainable development goals. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Heteroatoms in graphene-based materials modulate their electrochemical activity. • Supporting Ni on S,N-doped graphene decreases the HO 2 − route for ORR below 10% • Supporting Ni on doped graphene materials reduces HER overpotential ca. 0.50 V. • These Ni materials are promising electrocatalysts for alkaline PEM devices. In this work, Ni nanoparticles (NPs), with nominal metallic loading of 20 wt%, were deposited on graphene-based materials (GMs) doped with nitrogen and sulphur, in order to study their electrocatalytic activity towards the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) in alkaline medium. Different chemical reducing agents were employed to synthesize the catalysts. Results indicate that the presence of heteroatoms in the GMs influences the activity of both the GMs and the Ni-based catalysts. Thus, best results were obtained for catalyst containing nitrogen and sulphur for the ORR which favours the direct four-electron pathway, whereas for the HER, the highest performance was observed for N -doped materials. [ABSTRACT FROM AUTHOR]

• Various classes of electrocatalysts for O 2 activation are highlighted. • Modification, and ORR activity of TMOs, TMSs, TMPs, SACs and DACs are provided. • Selectivity, catalytic activity, and durability of M-N-C catalysts are discussed. • Challenges and future prospects with M-N-C electrocatalysts are emphasized. Electrocatalytic oxygen reduction reaction (ORR) is essential in fuel cells and metal-air batteries for converting and storing energy. Nevertheless, these devices suffer from ORR's slow kinetics at cathode surfaces, necessitating effective electrocatalysts. To meet the practical application of these devices, various ORR electrocatalysts, including transition metal oxides (TMOs), sulfides (TMSs), phosphides (TMPs), and single-atom catalysts (SACs), have been developed, each with its issues related to limited activity, selectivity, and durability. Although TMOs possessed promise towards ORR, their limited conductivity and poor selectivity motivated the researcher to perform their sulfurization and phosphorization, resulting in TMSs, TMPs, and SACs, which displayed good ORR. However, at a practical level, these catalysts still exhibited poor selectivity and durability, introducing a novel class of electrocatalysts, 'dual-atom catalysts (DACs)'. DACs have many advantages, including maximum atomic utilization in catalysis and a well-established activity descriptor, over other electrocatalysts. However, an assessment of DAC's evolution, their promise towards ORR, and the learned concepts to design efficient ORR catalysts is required. The purpose of this review is to provide a road map of the transition of electrocatalysts from TMOs to DACs with recent advancements in chemistry, structural-functional relationships, advantages, and disadvantages. In addition, the challenges, and relative prospects of various critical parameters of ORR electrocatalysts are also covered systematically. [Display omitted] [ABSTRACT FROM AUTHOR]

The Pt 7 Ni 3 /C catalyst with heat treatment increased the conductivity by reducing oxygen bonding as well as changing the structure into an ordered FCT structure with good activity in PEMFCs. [Display omitted] • The Pt 7 Ni 3 /C catalyst with heat treatment at 700 °C exhibited excellent catalytic activity and stability. • The crystalline properties and long term durability performance of PtNi catalysts exhibited good evidence to improve ORR. • Pt 7 Ni 3 /C catalyst with heat treatment changed into an ordered FCT structure with excellent electrochemical performance. Demand for replacing the Pt catalyst in proton exchange membrane fuel cells (PEMFCs) has increased because Pt metal is rare and high cost. The most reasonable way is synthesizing Pt-base alloy using transition metals such as Co, Ni, Fe, and Mo. The Pt-based alloy catalysts exhibit excellent catalytic activity by creating a synergistic effect through the interaction between Pt and the transition metals. Here we present the best PtNi alloy composition and maximize the performance of the oxygen reduction reaction (ORR) activity in fuel cells by annealing the alloy under a hydrogen atmosphere. The Pt 7 Ni 3 /C catalyst indicated a higher ORR activity than other compositions due to different structural changes, and the annealing catalysts at 700 °C under an H 2 atmosphere improved the electrochemical activity and stability. The heat treatment increased the conductivity by reducing oxygen bonding as well as changing the structure into an ordered face-centered tetragonal (FCT) structure with good activity. The result of these studies provides a new way to develop high-performance and low-cost catalyst materials for fuel cells. [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]

[Display omitted] • A highly curved and ultrathin P-doped PdMo bimetallene is engineered. • The catalyst has superior performance in electrooxidation of various alcohols. • The activity for ORR surpasses that of commercial Pt/C catalyst. • DFT reveals that P doping enhances both OH adsorption and CO desorption. The commercialization of direct alcohol fuel cells (DAFCs) relies on the development of high performance electrocatalysts for both the alcohol oxidation reaction and the oxygen reduction reaction (ORR). In this study, a novel phosphorus-doped palladium-molybdenum (P-PdMo) bimetallene with a partially amorphous structure is demonstrated. The ultrathin and curved morphology of the nanosheets, combined with electronic regulation by phosphorus atoms, facilitates OH adsorption and CO desorption. Consequently, the catalyst exhibits significantly enhanced activity and durability in the electrooxidation of alcohols, including methanol, ethanol, ethylene glycol, and glycerol. Particularly toward ethanol oxidation, the P-PdMo bimetallene displays exceptional mass and specific activities up to 4.95 A mg-1 Pd and 8.28 mA cm−2, respectively. Furthermore, the P-PdMo bimetallene demonstrates outstanding ORR performance, with an onset potential of 1.0 V and a half-wave potential of 0.88 V. Overall, this study opens new avenues in metallene electrocatalysts and advancing toward the practical implementation of DAFCs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Lamellar structured Ce-S-NC was synthesized with the sheet thickness of 2–3 nm. • Ce-S-NC was applied as the cathode catalyst in alkaline DMFC and DBFC. • Ce-S-NC cathode catalyst shows excellent durability at high current density. • Ce-S-NC are beneficial to improve mass transfer at cathode. Passive direct liquid fuel cells are promising power generation devices with the advantages of convenient transportation, storage for liquid fuel and high power density. This paper focuses on improving the intrinsic electrocatalytic performance and durability of nitrogen-doped carbon (N-C) cathodic electrocatalysts. Then, lamellar structured Ce-S-NC heterogeneous electrocatalyst was synthesized and used as a highly durable cathode for two types of passive direct liquid fuel cells, i.e. , direct methanol fuel cells (DMFCs) and direct borohydride fuel cells (DBFCs). In this work, the effect of the S/C molar ratio on the microstructure and electrocatalytic performance of the Ce-S-NC electrocatalysts was investigated, and excellent intrinsic oxygen reduction reaction activity was obtained at an S/C molar ratio of 0.15. The peak power densities of Ce-S-NC based DMFCs reached up to 12.5, 23.6 and 41.9 mW·cm−2 at 20, 40 and 60 °C, respectively. The peak power densities of 59.3, 84.6 and 132.6 mW·cm−2 were obtained in Ce-S-NC based DBFCs at 20, 40 and 60 °C, respectively. In the durability tests, both the Ce-S-NC based air-breathing DBFCs and passive DBFCs showed the stable operation than that of N-C and Ce-NC. When the current density increased from 50 to 150 mA·cm−2, the Ce-S-NC based DBFC can be operated for 882 h, and only 34 and 91 h for that of N-C and Ce-NC. The electrochemical impedance spectroscopy tests proved Ce-S-NC based DBFC showed the faster mass transfer efficiency. The outstanding durability of Ce-S-NC is mainly attributed to the improved defect density and mass transfer. [ABSTRACT FROM AUTHOR]

Efficient and stable electrocatalysts with low platinum content are crucial for the practical application of fuel cells. The development of Pt-based single atom catalysts (SACs) has emerged as a promising research direction. In this study, we design and prepare a SACs based on MoS 2 with Pt–S–Mo and Pd–S–Mo active sites (Pd, Pt–MoS 2) by successively occupying vacancies, while maintaining the individual characteristics of the active sites. The resulting Pd, Pt–MoS 2 catalyst exhibits excellent electrocatalytic activity for oxygen reduction reaction (ORR), long-term stability, and resistance to common poisons (SCN−, S2−, and methanol) under neutral conditions. Meanwhile, the microbial fuel cell (MFC) equipped with Pd, Pt–MoS 2 exhibits excellent performance in terms of actual electricity generation performance and sewage purification capacity with an ultrahigh power density, average chemical oxygen demand (COD) removal rate, and coulombic efficiency (CE) of 1398.6 ± 43.5 mW m−2, 96.2 ± 2.2 %, and 22.5 ± 0.5 %, respectively. This strategy will provide new insights into the development of advanced bimetallic as well as polymetallic doped vacancies of MoS 2 SACs. [Display omitted] • A feasible approach for the design of bimetallic single atom catalysts. • One SACs based on MoS 2 was prepared by successively occupying vacancies. • Pd, Pt–MoS 2 catalyst exhibits excellent electrocatalytic activity for ORR. • Optimized catalyst exhibits excellent capacity in electricity generation. [ABSTRACT FROM AUTHOR]

Advancements in inexpensive, efficient, and durable oxygen reduction catalysts is important for maintaining the sustainable development of fuel cells. Although doping carbon materials with transition metals or heteroatomic doping is inexpensive and enhances the electrocatalytic performance of the catalyst, because the charge distribution on its surface is adjusted, the development of a simple method for the synthesis of doped carbon materials remains challenging. Here, a non-precious-metal tris (Fe/N/F)-doped particulate porous carbon material (21P2-Fe1-850) was synthesized by employing a one-step process, using 2-methylimidazole, polytetrafluoroethylene, and FeCl3 as raw materials. The synthesized catalyst exhibited a good oxygen reduction reaction performance with a half-wave potential of 0.85 V in an alkaline medium (compared with 0.84 V of commercial Pt/C). Moreover, it had better stability and methanol resistance than Pt/C. This was mainly attributed to the effect of the tris (Fe/N/F)-doped carbon material on the morphology and chemical composition of the catalyst, thereby enhancing the catalyst’s oxygen reduction reaction properties. This work provides a versatile method for the gentle and rapid synthesis of highly electronegative heteroatoms and transition metal co-doped carbon materials.

The high cost and poor reliability of cathodic electrocatalysts for the oxygen reduction reaction (ORR), which requires significant amounts of expensive and scarce platinum, obstructs the broad applications of proton exchange membrane fuel cells (PEMFCs). The principles of ORR and the reasons for the poor stability of Pt-based catalysts are reviewed. Moreover, this paper discusses and categorizes the strategies for enhancing the stability of Pt-based catalysts in fuel cells. More importantly, it highlights the recent progress of Pt-based stability toward ORR, including surface-doping, intermetallic structures, 1D/2D structures, rational design of support, etc. Finally, for atomic-level in-depth information on ORR catalysts in fuel cells, potential perspectives are suggested, such as large-scale preparation, advanced interpretation techniques, and advanced simulation. This review aims to provide valuable insights into the fundamental science and technical engineering for practical Pt-based ORR electrocatalysts in fuel cells.

Zeolitic Imidazolate Frameworks (ZIFs) derived nitrogen‐doped porous carbon (NPC) materials have been proposed as promising metal‐free electrocatalysts for oxygen reduction reactions (ORR). Herein, we report a strategy to control the morphology of ZIF‐8 and ZIF material‐derived NPC materials by the amount of L‐cysteine. The prepared NPC electrocatalysts exhibit different morphologies and ORR properties. The best of these catalysts exhibited a nanosheet‐like morphology with an onset potential of 0.95 V and a half‐wave potential of 0.87 V in alkaline media, which are comparable to those of commercial Pt/C (20 wt%) catalysts. In addition, this catalyst exhibited high stability and methanol resistance. This work not only reveals the effect of L‐cysteine amount on the growth process of ZIF, but also provides a strategy for designing various excellent catalysts in the fuel cell field. [ABSTRACT FROM AUTHOR]

Opening up electrocatalysts for oxygen reduction reaction (ORR) is essential for practical application in fuel cells and metal-air batteries; however, how to make the catalysts with both good performance and low cost is difficult. Recently, research on the ORR of molybdenum disulfide-based catalysts in alkaline electrolytes has been on the rise. However, the development of MoS2 catalyst for acidic ORR is still in its infancy. Herein, without using reductant and morphology control reagent, we firstly obtained flowerball-like MoS2/Vulcan XC-72R (VC) nanocomposites via hydrothermal method. The designed composite exhibits a nearly 4e− ORR process with 0.78 and 0.92 V onset potentials in 0.1 M KOH and HClO4, respectively. Furthermore, the flowerball-like composite shows utmost electrochemical stability judging by 87 and 80% current retention for about 5.5 h either in alkaline or acid media, long term durability for continuous 10,000 cycles, and stronger resistance to methanol than the commercial Pt/C catalyst. The abundant Mo edges as catalytic active centers of flowerball-like structure, high electron conductivity, and enhanced mass transport in either alkaline or acidic electrolyte are favorable for catalytic performance. The prepared catalyst provides great potential for the substitution of noble metal based catalysts in fuel cells and metal-air batteries. [ABSTRACT FROM AUTHOR]

Fuel cells are a promising alternative to non-renewable energy production industries such as petroleum and natural gas. The cathodic oxygen reduction reaction (ORR), which makes fuel cell technology possible, is sluggish under normal conditions. Thus, catalysts must be used to allow fuel cells to operate efficiently. Traditionally, platinum (Pt) catalysts are often utilized as they exhibit a highly efficient ORR with low overpotential values. However, Pt is an expensive and precious metal, posing economic problems for commercialization. Herein, advances in carbon-based catalysts are reviewed for their application in ORRs due to their abundance and low-cost syntheses. Various synthetic methods from different renewable sources are presented, and their catalytic properties are compared. Likewise, the effects of heteroatom and non-precious metal doping, surface area, and porosity on their performance are investigated. Carbon-based support materials are discussed in relation to their physical properties and the subsequent effect on Pt ORR performance. Lastly, advances in fuel cell electrolytes for various fuel cell types are presented. This review aims to provide valuable insight into current challenges in fuel cell performance and how they can be overcome using carbon-based materials and next generation electrolytes. [ABSTRACT FROM AUTHOR]

Atomically dispersed metals stabilized by nitrogen elements in carbon skeleton hold great promise as alternatives for Pt-based catalysts towards oxygen reduction reaction in proton exchange membrane fuel cells. However, their widespread commercial applications are limited by complicated synthetic procedures for mass production. Herein, we are proposing a simple, green mechanochemical approach to synthesize zeolitic imidazolate frameworks precursors for the production of atomically dispersed "Fe-N4" sites in holey carbon nanosheets on a large scale. The thin porous carbon nanosheets (PCNs) with atomically dispersed "Fe-N4" moieties can be prepared in hectogram scale by directly pyrolysis of salt-sealed Fe-based zeolitic imidazolate framework-8 (Fe-ZIF-8@NaCl) precursors. The PCNs possess large specific surface area, abundant lamellar edges and rich "Fe-N4" active sites, and show superior catalytic activity towards oxygen reduction reaction in an acid electrolyte. This work provides a promising approach to cost-effective production of atomically dispersed transition metal catalysts on large scale for practical applications. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Donghua University (Natural Science Edition) is the property of Journal of Donghua University (Natural Science) Editorial Office 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.)

Exploring low‐cost and efficient oxygen reduction reaction (ORR) electrocatalysts is essential for clean energy conversion devices, such as fuel cells. Herein, a series of N, S co‐doped carbon‐based materials were synthesized by the one‐step pyrolysis route, using ZnCl2‐Zn(OH)2 as templates and solidago biomass as carbon and heteroatom sources. The double‐templated ZnCl2‐Zn(OH)2 system was employed to prepare the appealing carbon materials with hierarchical macro‐meso‐micro structure and high specific area. The invasive species of solidagos, as the precursors, have advantages of low cost and improved ecological diversification to some extent. The optimized catalyst (NSC‐Z2‐L) contains abundant hierarchical macro‐meso‐micro pores, high specific surface area (∼1581 m2 g−1) and N, S content (∼2.25 at.%). The special structure endows the catalyst with excellent ORR half‐wave potential (E1/2) of 0.85 V, 0.77 V and 0.76 V in the alkaline, acidic and neutral media, respectively, which are compatible with those of commercial Pt/C. The remarkable ORR performances are attributed to the hierarchically porous structure, high specific surface area and the synergistic effect of pyridinic‐N, graphitic‐N and C−S−C species. This work provides a valuable reference for achieving high‐performance ORR catalysts derived from low‐cost biomass materials. [ABSTRACT FROM AUTHOR]

Developing efficient and stable Pt‐based oxygen reduction reaction (ORR) catalysts is a way to promote the large‐scale application of fuel cells. Pt‐based alloy nanowires are promising ORR catalysts, but their application is hampered by activity loss caused by structural destruction during long‐term cycling. Herein, the preparation of ordered PtFeIr intermetallic nanowire catalysts with an average diameter of 2.6 nm and face‐centered tetragonal structure (fct‐PtFeIr/C) is reported. A silica‐protected strategy prevents the deformation of PtFeIr nanowires during the phase transition at high temperature. The as‐prepared fct‐PtFeIr/C exhibited superior mass activity for ORR (2.03 A mgPt−1) than disordered PtFeIr nanowires with face‐centered cubic structure (1.11 A mgPt−1) and commercial Pt/C (0.21 A mgPt−1). Importantly, the structure and electrochemical performance of fct‐PtFeIr/C were maintained after stability tests, showing the advantages of the ordered structure. [ABSTRACT FROM AUTHOR]

At present, fuel cell is considered to be one of the most ideal application technologies of hydrogen energy. In order to develop fuel cells on a large scale and in a sustainable way, low platinum or non-platinum oxygen reduction catalyst has become a research hotspot. In this work, a kind of doped carbon-based catalyst MPFe 1 Cu 1 -850 is prepared by high temperature synthesis. The catalyst has an ultra-thin lamellar porous structure. In an acidic medium, the MPFe 1 Cu 1 -850 displays good oxygen reduction reaction (ORR) activity (ΔE 1/2 = 0.725 V). In addition, it shows better stability (91%) and higher methanol tolerance than that of commercial Pt/C catalyst. In our catalyst MPFe 1 Cu 1 -850, the contents of nitrogen, iron and copper are 10.31 at.%, 0.51 at.%, and 0.50 at.%, respectively. This work shows that high N content, and the proper ratio of iron to copper (Fe:Cu = 1:1), are conducive to the enhancement of ORR activity. • Design a Fe and Cu bimetallic load on N- and F co-doped carbon material. • The N content of the doped carbon catalyst, MPFe 1 Cu 1 , is up 10.31 at.%. • When the ratio of Fe: Cu = 1, the ORR activity of the catalyst is enhanced. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) is a vital electrochemical reaction for energy conversion that has fascinated the interest of materials researchers to promote active and cost-effective electrocatalysts with improved reaction kinetics. Numerous, researches have been undertaken to achieve the desired characteristic cathode materials to revolutionize energy conversion devices including fuel cells and metal-air batteries (where ORR occurs). More importantly, the evaluation of electrocatalyst efficiency for ORR using typical electrochemical experiments, data collection, and analysis must be performed systematically and uniformly. This review provides a systematic guide to assess the electrochemical efficiency because it includes standard and widely recognized experimental protocols for each electrochemical technique, as well as easy-to-follow lab procedures and a detailed analysis of essential kinetic ORR parameters with a theoretical framework. The major function of each electrode in cyclic voltammetry, hydrodynamic linear scan voltammetry with rotating disc electrodes, and electrochemical impedance spectroscopy for ORR were demonstrated, as well as the construction of a three-electrode electrochemical cell. By following standard protocols and experimental procedures, an aspiring electrochemist would be capable to enforce fundamental and advanced electrochemical techniques much efficiently in their understanding of ORR kinetics evaluation. [Display omitted] • This review provides crucial insights and information on electrochemistry of ORR. • Overview on electrochemical techniques, measurements and calculation procedures. • The desired experimental approach for evaluating ORR electrocatalyst efficiency. • A beginner's guide to perform cathodic ORR for fuel cell applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Oxygen reduction reaction (ORR) has been extensively used in fuel cells and rechargeable metal-air batteries. • This review details the latest developments in ORR electrocatalyst development. • These electrocatalysts specifically include platinum group metals (PGM), transition metals and carbon-based catalysts. • The preparation and ORR performance of various electrocatalysts are discussed in detail. • Speculation and discussion on the development prospects and challenges of ORR electrocatalysts. Oxygen reduction reaction (ORR) has gradually been in the limelight in recent years because of its great application potential for fuel cells and rechargeable metal-air batteries. Therefore, significant issues are increasingly focused on developing effective and economical ORR electrocatalysts. This review begins with the reaction mechanisms and theoretical calculations of ORR in acidic and alkaline media. The latest reports and challenges in ORR electrocatalysis are traced. Most importantly, the latest advances in the development of ORR electrocatalysts are presented in detail, including platinum group metal (PGM), transition metal, and carbon-based electrocatalysts with various nanostructures. Furthermore, the development prospects and challenges of ORR electrocatalysts are speculated and discussed. These insights would help to formulate the design guidelines for highly-active ORR electrocatalysts and affect future research to obtain new knowledge for ORR mechanisms. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) is a critical process for several electrocatalytic and photocatalytic devices. Poly(3,4‐ethylenedioxythiophene), PEDOT, is an efficient ORR catalyst, with hydrogen peroxide (H2O2) being the primary reaction product. Although H2O2 is a green fuel for batteries and fuel cells and used as an industrial oxidant, it is toxic for living systems. As such, its production should be limited when PEDOT films are used in bioelectronic devices. In this work, the ORR behavior of a series of electropolymerized PEDOT films is investigated. By varying the counterion (monomeric vs polymeric), including a hydroxyl‐terminated EDOT monomer in the polymer architecture, or adding a conductivity enhancer in the reaction mixture, the authors aim to understand the parameters governing the ORR properties. It is that the polymer's pristine doping level—influenced by counterion type and the presence of the conductivity enhancer—controls the ORR pathway in PEDOT films. High levels of intrinsic doping led to films with H2O2 as the major ORR product. This work suggests strategies for the design of conducting polymers with optimized performance for electrocatalytic applications and minimized production of harmful chemicals for bioelectronic devices. [ABSTRACT FROM AUTHOR]

Herein, molybdenum disulfide nanoflakes decorated copper phthalocyanine microrods (CuPc-MoS 2) are synthesized via two step simple hydrothermal method. The as synthesized hybrid along with pure molybdenum disulfide (MoS 2) nanoflower and pure copper phthalocyanine (CuPc) microrods are well characterized by various techniques that confirm phase, morphology, elemental compositions etc. Next, electrocatalytic oxygen reduction reaction towards fuel cell is investigated in alkaline medium and obtained results proclaim that our CuPc-MoS 2 heterostructure outperforms the other two constituent materials. Efficient oxygen reduction is achieved following four electron pathway by CuPc-MoS 2 whereas partial reduction is done through two electron process by CuPc and MoS 2 separately. Long-time durability test reveals almost 97.6% retention after 8000s that eventually dictate us that CuPc-MoS 2 heterostructure can be the efficient cathode electrocatalyst for future generation fuel cell. [Display omitted] • Hierarchical growth of MoS 2 on CuPc rod is formed using low temperature facile route. • Enhanced electrocatalytic ORR of CuPc-MoS 2 is observed than bare counterparts. • Long-time durability test reveals almost 97.6% retention after 8000s for CuPc-MoS 2. • Structure activity relationship and active edge sites play role for enhanced ORR. [ABSTRACT FROM AUTHOR]

The replacement of Pt/C catalysts with iron−nitrogen−carbon (Fe−N−C) nanomaterials in the oxygen reduction reaction (ORR) is appealing for the large‐scale application of fuel cells. Herein, an extended Stöber method was used to in situ synthesize Fe−N co‐doped porous carbon spheres (Fe−N−Cs) with large surface areas and impressive ORR performance. Fe−N−Cs were synthesized using 3‐aminophenol as N precursor, ferrocenealdehyde (Fc−CHO) as Fe source and crosslinker, and Pluronic F127 as soft template. Among all prepared catalysts, Fe−N−Cs‐1.0 exhibits much enhanced ORR activities. The initial potential and half‐wave potential are 0.992 V, 0.873 V (vs. RHE) and 0.981 V, 0.871 V in alkaline and acidic media, respectively, which are higher than that of commercial Pt/C catalyst (0.986 V, 0.868 V and 0.979 V, 0.843 V). Meanwhile, the methanol tolerance and durability of Fe−N−Cs‐1.0 were far better than Pt/C. This work manifests the Fe−N−Cs electrocatalysts are expected to replace the commercial Pt/C catalyst in the area of ORR. [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) can take place either through a two‐electron pathway to form H2O2 or through a four‐electron pathway to form H2O. Both the reactions are important in the respective fields, viz. H2O2 production as well as fuel cell technology, and rational design of catalysts is mandatory to acquire high energy efficiency in both cases. Here, we report the structure‐electrochemical property correlation of a series of perovskite related brownmillerite compounds, Ba2In0.75M0.25O5 (M=Mn/Fe/Co/Ni/Cu), synthesized by solid‐state method. On transition metal doping, octahedral distortions were observed, and the highly disordered material tends to follow the 4e transfer mechanism. More symmetrical structures followed the 2e pathway to form H2O2 as the product with high peroxide selectivity. The distortion in the octahedral arrangement can be a descriptor to finetune the selectivity of the catalysts towards the 2e and 4e pathways of ORR. [ABSTRACT FROM AUTHOR]

A novel route for the valorization of waste into valuable products was developed. Surgical masks commonly used for COVID 19 protection by stopping aerosol and droplets have been widely used, and their disposal is critical and often not properly pursued. This work intended to transform surgical masks into platinum group metal‐free electrocatalysts for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) as well as into crude oil. Surgical masks were subjected to controlled‐temperature and ‐atmosphere pyrolysis, and the produced char was then converted into electrocatalysts by functionalizing it with metal phthalocyanine of interest. The electrocatalytic performance characterization towards ORR and HER was carried out highlighting promising activity. At different temperatures, condensable oil fractions were acquired and thoroughly analyzed. Transformation of waste surgical masks into electrocatalysts and crude oil can open new routes for the conversion of waste into valuable products within the core of the circular economy. [ABSTRACT FROM AUTHOR]

In this work copper oxide nanoparticles (CuONPs) are prepared from precursor CuSO4.5H2O using plant leaves extract (PEE) of Eranthemum pulchellum(E. pulchellum).The synthesized CuONPs are characterized by ultraviolet visible (UV‐vis) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X‐ray diffraction (XRD) and transmission electron microscopy (TEM). CuONPs are distorted spherical in shape, with the sizes ranging from 5 to 17 nm. PEE and CuONPs are coated on glassy carbon (GC) electrode and abbreviated as GC/PEE and GC/CuONPs, respectively. The modified electrodes GC/PEE and GC/CuONPs are characterized with cyclic voltammetry (CV) techniques. The modified electrode GC/CuONPs exhibits good electrocatalytic activity for oxygen reduction reaction (ORR). GC/CuONPs also shows excellent operational stability up to 1000 CV cycles. [ABSTRACT FROM AUTHOR]

The structurally ordered PtM with surface coating layers strategy has drawn increasing attention. In this work, we synthesize a structurally ordered PtFe@NC-X-PDA catalyst modified with nitrogen-doped carbon coating layers by confined space annealing strategy. Compared with the current commercial Pt/C catalyst, the structurally ordered PtFe@NC-X-PDA catalyst shows better catalytic activity and stability. Especially, the mass activity and specific activity of the synthesized PtFe@NC-0.06-PDA sample with the optimized poly-dopamine feeding mass content (0.06 g) exhibit 9.95 and 11.53 times higher than that of commercial Pt/C catalyst. In addition, after 20,000 CV cycles, the PtFe@NC-0.06-PDA sample achieves the minimum activity loss (7%). The PtFe alloy catalyst with the different thickness NC shell (PtFe@NC-X-PDA) possesses the enhanced ORR activity and stability owing to the protection of nitrogen carbon shell (NC) and the strong electronic interaction of the ordered PtFe NPs. The improved ORR activity and stability of the structurally ordered PtFe@NC-X-PDA catalyst provide a promising direction for the development of fuel cells. Herein, we have successfully achieved precise modulation of the nitrogen doped carbon coating layers thickness in situ and simultaneously regulation the interfacial or chemical ordering energy at the atomic level that possess enhanced catalytic ORR activity and stability. [Display omitted] • A confined space annealing strategy of poly-dopamine was proposed to improve the performance of PtFe nanoparticles. • The level of alloy degree is turned by the poly-dopamine feeding mass content. • The protection from NC shell and ordered structure collectively guarantee the stability of the catalyst. • The PtFe@NC-0.06-PDA catalyst with suitable NC shell thickness possesses enhanced oxygen reduction performance. [ABSTRACT FROM AUTHOR]