Electrocatalysts For Oxygen Reduction Reaction Research Articles

Recent Advances in Carbon-Based Single-Atom Catalysts for Electrochemical Oxygen Reduction to Hydrogen Peroxide in Acidic Media

Electrochemical oxygen reduction reaction (ORR) via the 2e− pathway in an acidic media shows great techno-economic potential for the production of hydrogen peroxide. Currently, carbon-based single-atom catalysts (C-SACs) have attracted extensive attention due to their tunable electronic structures, low cost, and sufficient stability in acidic media. This review summarizes recent advances in metal centers and their coordination environment in C-SACs for 2e−-ORR. Firstly, the reaction mechanism of 2e−-ORR on the active sites of C-SACs is systematically presented. Secondly, the structural regulation strategies for the active sites of 2e−-ORR are further summarized, including the metal active center, its species and configurations of nitrogen coordination or heteroatom coordination, and their near functional groups or substitute groups, which would provide available and proper ideas for developing superior acidic 2e−-ORR electrocatalysts of C-SACs. Finally, we propose the current challenges and future opportunities regarding the acidic 2e−-ORR pathway on C-SACs, which will eventually accelerate the development of the distributed H2O2 electrosynthesis process.

The current state of transition metal-based electrocatalysts (oxides, alloys, POMs, and MOFs) for oxygen reduction, oxygen evolution, and hydrogen evolution reactions

Climate change is showing its impacts now more than ever. The intense use of fossil fuels and the resulting CO2 emissions are mainly to blame, accentuating the need to develop further the available energy conversion and storage technologies, which are regarded as effective solutions to maximize the use of intermittent renewable energy sources and reduce global CO2 emissions. This work comprehensively overviews the most recent progress and trends in the use of transition metal-based electrocatalysts for three crucial reactions in electrochemical energy conversion and storage, namely, the oxygen evolution (OER), oxygen reduction (ORR), and hydrogen evolution (HER) reactions. By analyzing the state-of-the-art polyoxometalates (POMs) and metal-organic frameworks (MOFs), the performance of these two promising types of materials for OER, ORR, and HER is compared to that of more traditional transition metal oxides and alloy-based electrocatalysts. Both catalytic activity and stability are highly influenced by the adsorption energies of the intermediate species formed in each reaction, which are very sensitive to changes in the microstructure and chemical microenvironment. POMs and MOFs allow these aspects to be easily modified to fine-tune the catalytic performances. Therefore, their chemical tunability and versatility make it possible to tailor such properties to obtain higher electrocatalytic activities, or even to obtain derived materials with more compelling properties towards these reactions.

ZIF-8 derived iron-, sulphur-, and nitrogen-doped catalysts for anion-exchange membrane fuel cell application

This study presents the preparation of tridoped Fe, N, S carbon-based catalysts using ZIF-8 as the main carbon source and iron(II)acetate, 1,10-phenanthroline, ammonia gas and thiourea as precursors for Fe, N and S elements. Thiourea was mixed via planetary ball-milling with a Fe–N–C catalyst prepared by inert gas pyrolysis, and different pyrolysis conditions were applied thereafter. The main goal of the work is to synthesise active non-precious metal electrocatalysts for oxygen reduction reaction (ORR). High electrocatalytic ORR activity in alkaline media was observed for the two materials obtained after thiourea addition and subsequent pyrolysis. Physico-chemical characterisation revealed successful S- and N-doping for all three catalysts with enhanced porosity for the two materials that were subjected to additional pyrolysis after the thiourea addition. The sulphur doping was highest for the FeNSC3 material that was subjected to a second pyrolysis in N2 and a third pyrolysis in NH3, compared to the FeNSC2 material that was subjected to a single pyrolysis in NH3 flow after thiourea addition. The ORR activity of FeNSC2 with half-wave potential of 0.88 V was slightly higher than that of FeNSC3, and the former was selected for evaluation as a cathode catalyst in an anion-exchange membrane fuel cell.

Enhanced Mass Activity and Durability of Bimetallic Pt-Pd Nanoparticles on Sulfated-Zirconia-Doped Graphene Nanoplates for Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cell Applications.

Developing highly active and durable Pt-based electrocatalysts is crucial for polymer electrolyte membrane fuel cells. This study focuses on the performance of oxygen reduction reaction (ORR) electrocatalysts composed of Pt-Pd alloy nanoparticles on graphene nanoplates (GNPs) anchored with sulfated zirconia nanoparticles. The results of field emission scanning electron microscopy and transmission electron microscopy showed that Pt-Pd and S-ZrO2 are well dispersed on the surface of the GNPs. X-ray diffraction revealed that the S-ZrO2 and Pt-Pd alloy coexist in the Pt-Pd/S-ZrO2-GNP nanocomposites without affecting the crystalline lattice of Pt and the graphitic structure of the GNPs. To evaluate the electrochemical activity and reaction kinetics for ORR, we performed cyclic voltammetry, rotating disc electrode, and EIS experiments in acidic solutions at room temperature. The findings showed that Pt-Pd/S-ZrO2-GNPs exhibited a better ORR performance than the Pt-Pd catalyst on the unsulfated ZrO2-GNP support and with Pt on S-ZrO2-GNPs and commercial Pt/C.

Tandem supported, high metal-loading, non-PGM electrocatalysts for oxygen reduction reaction

Developing non-platinum group metal (non-PGM) electrocatalysts for the oxygen reduction reaction (ORR) is a critical effort toward low-cost fuel cells and metal–air batteries. Such catalysts require a uniform dispersion of metal atoms on a solid support, typically consisting of nitrogen doped carbon. However, the synthesis of non-PGM electrocatalysts is often complex, and metal loadings are typically below 10 wt. %, limiting the number of active sites and, therefore, the catalytic activity. In this work, we overcome these limits by synthesizing tandem supported, copper loaded electrocatalysts. Through one-pot pyrolysis, we make carbon black/Cu-doped graphitic carbon nitride (g-C3N4) core–shell structures to optimize the trade-off between conductivity and metal-loading capacity and achieve a Cu loading larger than 20 wt. %. By controlling the pyrolysis temperature, we systematically modulate the catalyst composition, structure, electrocatalytic activity, and stability. At a low pyrolysis temperature of only 600 °C, we achieve an onset potential of 0.90 V and a half-wave potential of 0.81 V vs RHE for alkaline ORR and negligible current loss after 10 000 potential cycles. These results demonstrate an effective approach to realize non-PGM electrocatalysts with optimum metal-loading, activity, and stability, thus unlocking their potential for real-world applications.

Transforming Cigarette Wastes into Oxygen Reduction Reaction Electrocatalyst: Does Each Component Behave Differently? An Experimental Evaluation

AbstractTrillion of cigarette butts are annually littered without being recycled. This work aims at valorizing the whole cigarette butts and their components (paper, filter and tobacco) into Fe‐Nx‐C electrocatalysts for oxygen reduction reaction (ORR) in acid and alkaline media. The pristine wastes were pyrolyzed at 450 °C, activated with KOH at 700 °C, blended with iron phthalocyanine (FePc) precursor, and heat‐treated at 600 °C to produce a robust Fe‐Nx‐C material with ORR active units. The effect of the cigarette components on the final electrocatalytic activity was evaluated by thoroughly investigating the surface chemistry with XPS. The electrocatalysts displayed similar results among the different components in both media due to comparable surface chemistry, especially concerning the nitrogen functional groups. The highest performance was obtained in alkaline where the electrocatalysts from whole cigarettes and paper (CIGF_450 and CIGPF_450) showed an E1/2 of 0.89 V vs RHE, slightly larger than that of Pt/C with 40 wt % of Pt, which encouraged to replace Pt‐based electrocatalysts in alkaline fuel cells.

Chitosan-derived carbon sphere with self-activating behavior for stable oxygen reduction reaction in acid and alkaline media

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 (H2O2) of 5 % and 8 % in 0.1 M KOH and 0.5 M H2SO4, 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 H2SO4 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.

The manipulation of rectifying contact of Co and nitrogen‐doped carbon hierarchical superstructures toward high‐performance oxygen reduction reaction

AbstractRational design and construction of oxygen reduction reaction (ORR) electrocatalysts with high activity, good stability, and low price are essential for the practical applications of renewable energy conversion devices, such as metal‐air batteries. Electronic modification through constructing metal/semiconductor Schottky heterointerface represents a powerful strategy to enhance the electrochemical performance. Herein, we demonstrate a concept of Schottky electrocatalyst composed of uniform Co nanoparticles in situ anchored on the carbon nanotubes aligned on the carbon nanosheets (denoted as Co@N‐CNTs/NSs hereafter) toward ORR. Both experimental findings and theoretical simulation testify that the rectifying contact could impel the voluntary electron flow from Co to N‐CNTs/NSs and create an internal electric field, thereby boosting the electron transfer rate and improving the intrinsic activity. As a consequence, the Co@N‐CNTs/NSs deliver outstanding ORR activity, impressive long‐term durability, excellent methanol tolerance, and good performance as the air‐cathode in the Zn‐air batteries. The design concept of Schottky contact may provide the innovational inspirations for the synthesis of advanced catalysts in sustainable energy conversion fields.

Exploring Advanced Oxygen Reduction Reaction Electrocatalysts: The Potential of Metal-Free and Non-Pyrolyzed Covalent Organic Frameworks.

Oxygen reduction reaction (ORR) electrocatalysis is an area of increasing interest for the in-situ production of H2O2 or the development of energy-related devices such as hydrogen fuel cells. Although pyrolyzed catalysts still offer the best performances to date with reference to the organic-based catalysts, metal-free and non-pyrolyzed covalent organic frameworks (COFs) stands out as promising alternatives candidates due to their favourable characteristics such as crystallinity, porosity, and organic composition, allowing the study of structural-property relationships. Herein, we present the design principles and recent advances in COFs-based ORR electrocatalysts, demonstrating how composition influences the activity and electronic pathway of the oxygen reduction process.

In-situ generation of enhanced Pd-Co nanoparticles using various stabilizing agents decorated on reduced graphene oxide as electrocatalyst for oxygen reduction reaction

The synthesis and characterization of PdCo nanoparticles deposited on reduced graphene oxide as an electrocatalyst for the oxygen reduction reaction have been successfully carried out. This research aims to investigate the influence of various stabilizing agents on the character of the metal nanoparticles towards the activity of the oxygen reduction reaction (ORR). Reduced graphene oxide (RGO) acts as a supporting material for the PdCo nanoparticles. This material was produced from graphite as a raw material that was oxidized using the Tour method. The PdCo/RGO material was synthesized by in-situ generation with the various stabilizing agent types of cetyltrimethylammonium bromide (CTAB), hexamethylenetetramine (HMTA) and a combination of CTAB-HMTA. The results showed that the optimal stabilizing agent type for PdCo/RGO is HMTA (PdCo-H/RGO), giving PdCo nanoparticles with the smallest size, the most uniform shape and the most dispersion on the RGO surface. The ORR catalytic test showed that PdCo-H/RGO displayed activity, with the number of electron transfers being 3.64, which follows the direct 4-electron reduction pathway of the ORR. The catalyst stability test showed that PdCo-H/RGO had relatively high durability with an E1/2 negative shift of 57.6 mV.

Boosting oxygen reduction durability by embedding Co9S8 nanoparticles into Co single atoms anchored porous carbon frameworks

Developing an efficient and low-cost oxygen reduction electrocatalyst is essential for the application of aqueous zinc-air batteries (ZABs). Herein, we report a facile adsorption-confined pyrolysis strategy to fabricate the hybrid electrocatalyst (denoted as Co9S8/CoSA-PC) by embedding Co9S8 nanoparticles into Co single atoms (Co-SAs) anchored porous carbon sheets for boosting oxygen reduction reaction (ORR) durability. In this strategy, the Co2+ ions are first absorbed into oxygen-rich porous carbon nanosheets and further form the Co-SAs with the help of thiourea in the following pyrolysis procedure, which is believed to be able to confine the generated Co9S8 nanoparticles into carbon frameworks due to their interface interaction. Benefiting from the synergistic effect of different components, the obtained Co9S8/CoSA-PC electrocatalyst for ORR exhibits outstanding catalytic activity with a half-wave potential of 0.82 V and a distinguished long-term durability with a current retention of 80 % after cycling 80 h under alkaline conditions, which is superior to commercial Pt/C. Moreover, the assembled ZABs with Co9S8/CoSA-PC as cathodic catalyst deliver a high specific capacity of 764 mAh gZn−1 at 10 mA cm−2 and the outstanding peak power density of up to 221.4 mW cm−2. This work provides a novel structure design strategy to prepare transition metal sulfide-based electrocatalysts with superior durability for ORR.

Bimetallic Organic Frameworks via In Situ Solvothermal Sol-Gel-Crystal and Sol-Crystal Transformation as Durable Electrocatalysts for Oxygen Reduction Reaction.

The in situ solvothermal conversion of metal-organic gels (MOGs) to crystalline metal-organic frameworks (MOFs) represents a versatile and ingenious strategy that has been employed for the synthesis of MOF materials with specific morphologies, high yield, and improved functional properties. Herein, we have adopted an in situ solvothermal conversion of bimetallic MOGs to crystalline bimetallic MOFs with the aim of introducing a redox-active metal heterogeneity into the monometallic counterpart. The formation of bimetallic NiZn-MOF and CoZn-MOF via in situ solvothermal sol-gel-crystal and sol-crystal transformation is found to depend on the solvent systems used. The sol-to-gel-to-crystal transformation of NiZn-MOF via the formation of NiZn-MOG is found to occur through the gradual disruption of gel fibers leading to subsequent formation of microcrystals and single crystals of NiZn-MOF. These bimetallic MOFs and MOGs serve as promising electrocatalysts for oxygen reduction reaction (ORR) with an excellent methanol tolerance property, which can be attributed to the enhanced mass and charge transfer, higher oxygen vacancies, and bimetallic synergistic interactions among the heterometals. This work demonstrates a convenient strategy for producing bimetallic MOGs to MOFs through the introduction of a redox-active metal heterogeneity in the inorganic hybrid functional materials for fundamental and applied research. Our results connect MOGs and MOFs which have been regarded as having opposite physical states, that is, soft vs hard, and provide promising structural correlation between MOGs and MOFs at the molecular level.

Unraveling the Tandem Effect of Nitrogen Configuration Promoting Oxygen Reduction Reaction in Alkaline Seawater

AbstractDeveloping seawater‐based high‐performance oxygen reduction reaction (ORR) electrocatalysts is meaningful to renewable energy storage and conversion, and the Fe‐based derivatives encapsulated by nitrogen (N) doped carbon are the typical representative. Nevertheless, unrevealing the mechanism of N configuration to ORR activity and chlorine resistance is still a great challenge. In this work, a feasible strategy is developed to prepare controllable pyridinic/pyrrolic‐N doped carbon‐coated Fe‐based electrocatalysts (FexN‐NC). Drawing support from the H3PO4 blocking based in situ Fourier transform infrared spectroscopy (FTIR) test and density‐functional theory (DFT) calculation, the tandem effect of pyridinic‐N and pyrrolic‐N on ORR is proved. Additionally, the low hydrogen peroxide (H2O2) yield and 4e− pathway of FexN‐NC demonstrate that N doping effectively reduces the adsorption of Cl−, which is consistent with the low Cl− adsorption energy of DFT. The half‐wave potential (E1/2) of FexN‐NC for ORR reaches 0.874 V in alkaline seawater, and ZABs assembled with FexN‐NC as the air cathode deliver a remarkable power density (162 mW cm−2), along with excellent long‐term durability (>400 h).

Co-Incorporated N-Doped Micro–Meso Porous Carbon as an Electrocatalyst for Oxygen Reduction Reaction and Zn–Air Battery

Co-Incorporated N-Doped Micro–Meso Porous Carbon as an Electrocatalyst for Oxygen Reduction Reaction and Zn–Air Battery

P and O Co‐Doped Pt‐Co Octahedral Nanocrystals as Highly Active and Stable Electrocatalysts for Oxygen Reduction Reaction

The development of high active and stable Pt‐M (M = transition metals) electrocatalysts for oxygen reduction reaction (ORR) is crucial for the commercialization of proton exchange membrane fuel cells (PEMFCs). The main challenge of Pt‐M electrocatalysts is their instability, mainly due to the leaching of M. In this study, we report the design of P and O co‐doped octahedral PtCo alloy on Ketjen carbon black (Px‐Oct PtCo/C) through a seed‐mediated synthesis. In‐situ FTIR spectroscopy revealed that P0.61‐Oct PtCo/C has the lowest d‐band center, thereby enhancing the catalytic activity. The strong interaction formed by chemical bond between O and Co in Px‐Oct PtCo/C, observed by EXAFS spectra effectively inhibited the dissolution of Co and improved the ORR stability. The mass activity and specific activity of P0.61‐Oct PtCo/C can reach 0.61 A mgPt‐1 and 2.4 mA cm‐2, respectively, which is 4.1 times and 10.9 times higher than that of commercial Pt/C. After 50,000 potential cycles, the loss of mass activity is only 25%, surpassing the DOE 2025 target of less than 40% loss after 30,000 cycles. This study offers an alternative approach to enhancing the activity and durability of Pt‐M electrocatalysts for the ORR.

Synthesis and characterization of metal–organic framework (MOF): importance in electro-catalysts for oxygen reduction reaction

Synthesis and characterization of metal–organic framework (MOF): importance in electro-catalysts for oxygen reduction reaction

Catalytically Active Carbon for Oxygen Reduction Reaction in Energy Conversion: Recent Advances and Future Perspectives.

The shortage and unevenness of fossil energy sources are affecting the development and progress of human civilization. The technology of efficiently converting material resources into energy for utilization and storage is attracting the attention of researchers. Environmentally friendly biomass materials are a treasure to drive the development of new-generation energy sources. Electrochemical theory is used to efficiently convert the chemical energy of chemical substances into electrical energy. In recent years, significant progress has been made in the development of green and economical electrocatalysts for oxygen reduction reaction (ORR). Although many reviews have been reported around the application of biomass-derived catalytically active carbon (CAC) catalysts in ORR, these reviews have only selected a single/partial topic (including synthesis and preparation of catalysts from different sources, structural optimization, or performance enhancement methods based on CAC catalysts, and application of biomass-derived CACs) for discussion. There is no review that systematically addresses the latest progress in the synthesis, performance enhancement, and applications related to biomass-derived CAC-based oxygen reduction electrocatalysts synchronously. This review fills the gap by providing a timely and comprehensive review and summary from the following sections: the exposition of the basic catalytic principles of ORR, the summary of the chemical composition and structural properties of various types of biomass, the analysis of traditional and the latest popular biomass-derived CAC synthesis methods and optimization strategies, and the summary of the practical applications of biomass-derived CAC-based oxidative reduction electrocatalysts. This review provides a comprehensive summary of the latest advances to provide research directions and design ideas for the development of catalyst synthesis/optimization and contributes to the industrialization of biomass-derived CAC electrocatalysis and electric energy storage.

Dimetallic praseodymium-cobalt carbon nanotubes as highly efficient electrocatalyst for oxygen reduction reaction

In this study, six bimetallic rare earth (RE = La, Ce, Pr, Nd, Sm, Eu) cobalt nitrogen doped carbon nanotubes (RECo-NCNTs) were synthesized with g-C3N4 derivative method. These RECo-NCNTs were characterized by SEM, BET, XPS, XRD and Raman. In addition, their catalytic performances for oxygen reduction reaction (ORR) had also been tested. The introduction of rare earths did not destroy the structure of nanotubes but apparently change their ORR performances. The PrCo-NCNTs showed the significant improvement in catalytic ability for ORR (onset potential of 0.95 V and half-wave potential of 0.79 V), which is very close to that of commercial 20 % Pt/C. Moreover, PrCo-NCNTs exhibits an excellent catalytic stability (no activity decay after 10000st cycles) and an outstanding methanol toxic tolerance. Assembled in metal–air batteries (Zn-air, Al-air and Mg-air), the PrCo-NCNTs electrode also presents high power densities and discharge voltages.

Macrocycle-based covalent-organic-polymer as efficient oxygen electrocatalysts for zinc-air flow batteries

Covalent organic polymers (COPs), as emerging porous materials with well-defined architectures and high hydrothermal stability, have attracted extensive attention in the field of electrocatalysis. Herein, we report a rational design method for preparing oxygen reduction reaction electrocatalysts with the assistance of a predesigned macrocyclic COP model molecular. With the predesigned nitrogen position and structural features in macrocyclic chain-like COP-based materials, the obtained COPMCT-Co-900 catalyst provided excellent oxygen reduction performance, where the half-wave potential (E1/2) reaches 0.85 V (vs . RHE), comparable to commercial Pt/C. We also extended the strategy to similar macrocycle COPs and Fe-based and Ni-based metal sources and studied the oxygen reduction reaction performance of corresponding catalysts, proving the universality of the method. Interestingly, we assemble COPMCT-Co-900 catalyst as air electrode catalyst of the self-made rechargeable zinc-air flow batteries, which exhibit outstanding power density (155.6 mW·cm-2) and long cycle life (90 h, 270 cycles at 10 mA·cm-2). Our studies provide a new method for the development of high-performance oxygen electrodes applied in zinc-air flow battery devices.

Understanding amorphous PrOx-based N-doped carbon catalyst as an efficient electrocatalyst for oxygen reduction reaction

Understanding amorphous PrOx-based N-doped carbon catalyst as an efficient electrocatalyst for oxygen reduction reaction