Electrocatalysts For Oxygen Reduction Reaction Research Articles

Multiscale Understanding of Anion Exchange Membrane Fuel Cells: Mechanisms, Electrocatalysts, Polymers, and Cell Management.

Anion exchange membrane fuel cells (AEMFCs) are among the most promising sustainable electrochemical technologies to help solve energy challenges. Compared to proton exchange membrane fuel cells (PEMFCs), AEMFCs offer a broader choice of catalyst materials and a less corrosive operating environment for the bipolar plates and the membrane. This can lead to potentially lower costs and longer operational life than PEMFCs. These significant advantages have made AEMFCs highly competitive in the future fuel cell market, particularly after advancements in developing non-platinum-group-metal anode electrocatalysts, anion exchange membranes and ionomers, and in understanding the relationships between cell operating conditions and mass transport in AEMFCs. This review aims to compile recent literature to provide a comprehensive understanding of AEMFCs in three key areas: i) the mechanisms of the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR) in alkaline media; ii) recent advancements in the synthesis routes and structure-property relationships of cutting-edge HOR and ORR electrocatalysts, as well as anion exchange membranes and ionomers; and iii) fuel cell operating conditions, including water management and impact of CO2. Finally, based on these aspects, the future development and perspectives of AEMFCs are proposed.

Well-Defined PtCo@Pt Core-Shell Nanodendrite Electrocatalyst for Highly Durable Oxygen Reduction Reaction.

The rational design of efficient electrocatalysts with controllable structure and composition is crucial for enhancing the lifetime and cost-effectiveness of oxygen reduction reaction (ORR). PtCo nanocrystals have gained attention due to their exceptional activity, yet suffer from stability issues in acidic media. Herein, an active and highly stable electrocatalyst is developed, namely 3D Pt7Co3@Pt core-shell nanodendrites (NDs), which are formed through the self-assembly of small Pt nanoparticles (≈6nm). This unique structure significantly improves the ORR with an enhanced mass activity (MA) of 0.54 A mgPt -1, surpassing that of the commercial Pt/C (com-Pt/C) catalyst by three fold (0.17 A mgPt -1). The well-organized dendritic morphology, along with the Pt-rich shell, contributes significantly to the observed high catalytic activity and superior stability for acidic ORR, which exhibit a loss of 2.1% in MA and, impressively, an increase of 12.0% in specific activity (SA) after an accelerated durability test (ADT) of 40,000 potential-scanning cycles. This work offers insights for improving the design of highly stable Pt-based electrocatalysts for acidic ORR.

ZIF-8-derived Fe/P/N-co-doped carbon as efficient electrocatalysts for oxygen reduction reaction and zinc–air batteries

A facile method for preparing P-doped Fe–N–C catalysts for zinc–air batteries. The effect of P atoms on both Fe–Nx active sites and carbon substrates enhances catalytic activity.

Nano-alloy Anchored on Spent Coffee Grounds-derived N-doped Carbon Frameworks for Enhanced Oxygen Reduction Reaction and Oxygen Evolution Reaction

Development of efficient electrocatalyst for oxygen reduction reactions from earth abundant resources is crucial for fuel cells. In this work, the biomass of spent coffee grounds (SCGs) was used as...

Innovative strategies for designing and constructing efficient fuel cell electrocatalysts.

Polymer electrolyte membrane fuel cells (PEMFCs) are one of the most promising energy conversion devices due to their high efficiency and zero emission; however, two major challenges, high cost and short lifetime, have been hindering the commercialization of fuel cells. Achieving low-Pt or non-precious metal oxygen reduction reaction (ORR) electrocatalysts is one of the main research ideas in this field. In this review, the degradation mechanism of Pt-based catalysts is firstly explained and elucidated, and then five strategies are suggested for the reduction of Pt usage without loss of activity and durability: modulation of metal-support interactions, optimization of local ionomers and mass transport, modulation of composition, modulation of structure, and multi-site synergistic effects. For carbon-based non-precious metal catalysts, the problems and challenges faced by heteroatom/transition-metal doped carbon-based catalysts are discussed, and several strategies to improve the activity of heteroatom/transition-metal doped carbon catalysts are suggested. Particularly, an innovative quantum well catalyst structure reported quite recently is presented which may open up new prospects for the development of fuel cell technology. Finally, this review concludes with a brief conclusion and prospects for future development of low-Pt and non-precious metal fuel cell electrocatalysts.

Sm1-XSrxMnO3 (X = 0.1, 0.2, 0.3, and 0.4) Perovskite (SSM) with A-Site Doping Optimized as Oxygen Reduction Reaction (ORR) Electrocatalyst

Sm1-XSrxMnO3 (X = 0.1, 0.2, 0.3, and 0.4) Perovskite (SSM) with A-Site Doping Optimized as Oxygen Reduction Reaction (ORR) Electrocatalyst

Reactive metal–support interaction of In2O3/crystalline carbon hybrid support for highly durable and efficient oxygen reduction reaction electrocatalyst

Reactive metal–support interaction of In2O3/crystalline carbon hybrid support for highly durable and efficient oxygen reduction reaction electrocatalyst

Impact of Transition Metals and Electrocatalyst Layer Thickness on the Pt‐Based Cathodes of Proton Exchange Membrane Fuel Cells – Do Multimetallic Electrocatalysts Necessarily Yield an Improved Performance?

AbstractThe interplay between i) cathodic electrocatalytic layer (EC layer) features of proton exchange membrane fuel cell (PEMFC), focusing on the oxygen reduction reaction (ORR) electrocatalyst (EC) and the Pt loading; and ii) the PEMFC performance and durability is evaluated. An innovative hierarchical “core–shell” carbon nitride multimetallic ORR electrocatalyst (“PtCuNi/C” H‐EC) is compared with a conventional Pt/C benchmark. The various contributions to PEMFC performance at beginning of test (BOT) are isolated and correlated to the physicochemical features of the ORR EC and the cathodic EC layer. The PEMFC durability is investigated extensively via accelerated stress tests (ASTs) mimicking long‐term operation. Particular attention is dedicated to determine how ageing affects: i) PEMFC cell voltage; and ii) the cathode electrochemically active surface area (ECSA). “Post‐mortem” studies are carried out to probe how ageing influences the cathodic EC layer features, including: i) chemical composition; ii) elements distribution; iii) EC morphology; and iv) structure and crystal size of the Pt‐based metal nanoparticles bearing the active sites. Integrating the experimental results allows to identify both the positive and the detrimental effects triggered by the introduction of transition metals (TMs) in the ORR EC on the factors modulating PEMFC performance and long‐term operation.

In Situ Synthesis of Co3O4 Nanoparticles on N-Doped Biochar as High-Performance Oxygen Reduction Reaction Electrocatalysts

The development of sustainable and high-performance oxygen reduction reaction (ORR) electrocatalysts is fundamental to fuel cell implementation. Non-precious transition metal oxides present interesting electrocatalytic behavior, and their incorporation into N-doped carbon supports leads to excellent ORR performance. Herein, we prepared a shrimp shell-derived biochar (CC), which was doped with nitrogen via a ball milling approach (N-CC), and then used as support for Co3O4 nanoparticles growth (N-CC@Co3O4). Co3O4 loading was optimized using three different amounts of cobalt precursor: 1.56, 2.33 and 3.11 mmol in N-CC@Co3O4_1, N-CC@Co3O4_2 and N-CC@Co3O4_3, respectively. Interestingly, all prepared electrocatalysts, including the initial biochar CC, presented electrocatalytic activity towards ORR. Both N-doping and the introduction of Co3O4 NPs had a significant positive effect on ORR performance. Meanwhile, the three composites showed distinct ORR behavior, demonstrating that it is possible to tune their electrocatalytic performance by changing the Co3O4 loading. Overall, N-CC@Co3O4_2 achieved the most promising ORR results, displaying an Eonset of 0.84 V vs. RHE, jL of −3.45 mA cm−2 and excellent selectivity for the 4-electron reduction (n = 3.50), besides good long-term stability. These results were explained by a combination of high content of pyridinic-N and graphitic-N, high ratio of pyridinic-N/graphitic-N, and optimized Co3O4 loading interacting synergistically with the porous N-CC support.

Chlorine Axial Coordination Activated Lanthanum Single Atoms for Efficient Oxygen Electroreduction with Maximum Utilization.

Currently, there are still obstacles to rationally designing the ligand fields to activate rare-earth (RE) elements with satisfactory intrinsic electrocatalytic reactivity. Herein, axial coordination strategies and nanostructure design are applied for the construction of La single atoms (La-Cl SAs/NHPC) with satisfactory oxygen reduction reaction (ORR) activity. The nontrivial LaN4Cl2 motifs configuration and the hierarchical porous carbon substrate that facilitates maximized metal atom utilization ensure high half-wave potential (0.91V) and significant robustness in alkaline media. The aqueous and flexible Zinc-air battery (ZAB) integrating La-Cl SAs/NHPC as the cathode catalyst exhibits a maximum power density of 260.7 and 68.5mW cm-2, representing one of the most impressive RE-based ORR electrocatalysts to date. Theoretical calculations have demonstrated that the Cl coordination evidently modulate the electronic structures of La sites, which promoted electron transfer efficiency by d-p orbital couplings. With enhanced electroactivity of La sites, the adsorptions of key intermediates are optimized to alleviate the energy barriers of the potential-determining step. Importantly, this preparation strategy is also successfully applied to other REs. This work provides perspectives for near-range electronic structure modulation of RE-SAs based on a nonplanar coordination micro-environment for efficient electrocatalysis.

Organogel Polymer Electrocatalysts for Two-Electron Oxygen Reduction.

Polymer gels, renowned for unparalleled chemical stability and self-sustaining properties, have garnered significant attention in electrocatalysis. Notably, organic polymer gels that exhibit temperature sensitivity and incorporate suitable polar nonvolatile liquids, enhance electronic conductivity, and impart distinct morphological features, but remain largely unexplored as electrocatalysts for oxygen reduction reaction (ORR). To address this issue, an innovative strategy is proposed for synergistic modulation of the rigidity of mainchain molecular skeleton and length of alkyl sidechains, enabling the development of organogel polymers with a sol-gel temperature-sensitive phase transition that promises high selectivity and enhanced activity in electrocatalytic processes. Notably, the shortening of alkyl sidechain length can significantly affect the gelation behavior and internal microstructure of the catalyst, which modifies the electron state, ultimately impacting the catalytic activity of the gel polymer catalysts. In particular, phenyl-containing Ph-FL1 with short alkyl sidechains demonstrates outstanding 2e- ORR activity in alkaline medium, achieving a remarkable hydrogen peroxide (H2O2) selectivity of 98.6% with an impressive yield of 4.08 mol g-1 h-1. This performance surpasses most metal-free carbon-based electrocatalysts. Through theoretical calculation, the carbon atom (site-3) of C═N group is identified as potential active sites, representing a significant advancement toward designing cost-effective and efficient ORR electrocatalysts.

Electrochemically Controlled Deposition of Low-Crystalline Covalent Organic Frameworks on Nanocarbon Electrode Toward Metal-Free Oxygen Reduction Electrocatalyst.

Morphology-controlled synthesis of covalent organic frameworks (COFs) offers significant potential for electrochemical applications. However, controlling the deposition of nanometer-scale COFs on carbon supports remains challenging due to the need for a slow COF generation rate and the dispersion of carbon supports in liquid-phase synthesis. In this study, nanometer-scale COF/carbon composites are fabricated using electrochemically generated acid (EGA) to assist in the formation of imine-type COFs, which are then deposited onto pre-cast nanocarbon supports on an electrode. A monomer combination of tri(4-aminophenyl)-1,3,5-triazine and 2,5-dimethoxybenzene-1,4-dicarboxaldehyde is utilized due to their suitable oxidation potentials, with 1,2-diphenylhydrazine serving as the EGA source. Through proton generation driven by electrolysis conditions, controlled COF formation is achieved at the single nanometer scale, ranging from 6 to 30nm, on various nanocarbon supports. The COF/carbon electrode is evaluated as an oxygen reduction reaction (ORR) electrocatalyst, demonstrating superior performance compared to other COF-based electrode materials containing the 1,3,5-triazine moiety. The findings experimentally validate the efficacy of the EGA-assisted COF deposition method for nanostructure construction and its ability to enhance the properties of COF-based electrodes through morphology tuning.

Decoupling Conductivity, Heterogeneous Electron Transfer Rate, and Diffusion in Organic Molecular Electrocatalysis: Oxygen Reduction Reaction on Poly(3,4-ethylenedioxythiophene).

The electrified production of hydrogen peroxide (H2O2) by oxygen reduction reaction (ORR) is attractive to increase the sustainability of chemical industry. Here the same chains of intrinsically conductive polymer, poly(3,4-ethylenedioxythiophene) (PEDOT) are utilized, as ORR electrocatalyst, while varying polymeric primary dopants (PSS and Nafion) and the level of secondary doping with DMSO. These changes modulate various properties of the film, such as its microscale organization and electronic conductivity. The aim here is to clearly decouple the rate of the heterogeneous electron transfer (HET) of ORR from the diffusion affected by electronic conductivity and the electrochemically available surface area. It is found that the rate of HET and the double layer capacitance are significantly affected by primary dopant. On the contrary, secondary doping shows very little effect on the rate of HET. However, such secondary doping resulted in the increase of both electrochemically available surface area and the diffusion through the polymer film. This effect is attributed to a few orders increase of the electronic conductivity in the film improving availability of the polymer for electron transfer. The enhancement of diffusion upon the secondary doping of conducting polymer is utilized to improve direct conversion of air into H2O2 on gas diffusion electrode.

Transition metal atom supported on N-terminated diamond (100) surface as an efficient electrocatalyst for oxygen evolution and reduction reactions

Transition metal atom supported on N-terminated diamond (100) surface as an efficient electrocatalyst for oxygen evolution and reduction reactions

A Molecular Catalyst-Driven Sustainable Zinc-Air Battery Assembly.

Bidirectional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalysts are key for molecular oxygen-centric renewable energy transduction via metal-air batteries. Here, a molecular cobalt complex is covalently tethered on a strategically functionalized silica surface that displayed both ORR and OER in alkaline media. The detailed X-ray absorbance spectroscopy (XAS) studies indicate that this catalyst retains its intrinsic molecular features while playing a central role during bidirectional electrocatalysis and demonstrating a relatively lower energy gap between O2/H2O interconversions. This robust molecular catalyst-silica composite (deposited on a porous carbon paper) is assembled along with a zinc foil and polymeric gel membrane to devise an active single-stack quasi-solid zinc-air battery (ZAB) setup. This quasi-solid ZAB assembly displayed impressive power density (60 mWcm-2@100 mAcm-2), specific capacity (818 mAh g-1@ 5mAcm-2), energy density (757 Whkg-1 @5mAcm-2), and elongated charging/discharging life (28 h). An appropriate assembly of these ZAB units is able to power practical electronic appliances, requiring ≈1.6-6.0V potential requirements.

Modulation in Spin State of Co3O4 Decorated Fe Single Atom Enables a Superior Rechargeable Zinc-Air Battery Performance.

High-performance bifunctional electrocatalyst for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is the keystone for the industrialization of rechargeable zinc-air battery (ZAB). In this work, the modulation in the spin state of Fe single atom on nitrogen doped carbon(Fe1-NC) is devised by Co3O4 (Co3O4@Fe1-NC), and a mediate spin state is recorded. Besides, the d band center of Fe is downshifted associated with the increment in eg filling revealing the weakened interaction with OH* moiety, resulting in a boosted ORR performance. The ORR kinetic current density of Co3O4@Fe1-NC is 2.0- and 5.6 times higher than Fe1-NC and commercial Pt/C, respectively. Moreover, high spin state is found for Co in Co3O4@Fe1-NC contributing to the accelerated surface reconstruction of Co3O4 witnessed by operando Raman and electrochemical impedance spectroscopies. A robust OER activity with overpotential of 352mV at 50mA cm-2 is achieved, decreased by 18 and 60mV by comparison with Co3O4@NC and IrO2. The operando Raman reveals a balanced adsorption of OH* species and its deprotonation leading to robust stability. The ZAB performance of Co3O4@Fe1-NC is 193.2mW cm-2 and maintains for 200h. Furthermore, the all-solid-state ZAB shows a promising battery performance of 163.1mW cm-2.

Structural Modulation of Nanographenes Enabled by Defects, Size and Doping for Oxygen Reduction Reaction

AbstractNanographenes are among the fastest‐growing materials used for the oxygen reduction reaction (ORR) thanks to their low cost, environmental friendliness, excellent electrical conductivity, and scalable synthesis. The perspective of replacing precious metal‐based electrocatalysts with functionalized graphene is highly desirable for reducing costs in energy conversion and storage systems. Generally, the enhanced ORR activity of the nanographenes is typically deemed to originate from the heteroatom doping effect, size effect, defects effect, and/or their synergistic effect. All these factors can efficiently modify the charge distribution on the sp2‐conjugated carbon framework, bringing about optimized intermediate adsorption and accelerated electron transfer steps during ORR. In this review, the fundamental chemical and physical properties of nanographenes are first discussed about ORR applications. Afterward, the role of doping, size, defects, and their combined influence in boosting nanographenes’ ORR performance is introduced. Finally, significant challenges and essential perspectives of nanographenes as advanced ORR electrocatalysts are highlighted.

Structural Modulation of Nanographenes Enabled by Defects, Size and Doping for Oxygen Reduction Reaction.

Nanographenes are among the fastest-growing materials used for the oxygen reduction reaction (ORR) thanks to their low cost, environmental friendliness, excellent electrical conductivity, and scalable synthesis. The perspective of replacing precious metal-based electrocatalysts with functionalized graphene is highly desirable for reducing costs in energy conversion and storage systems. Generally, the enhanced ORR activity of the nanographenes is typically deemed to originate from the heteroatom doping effect, size effect, defects effect, and/or their synergistic effect. All these factors can efficiently modify the charge distribution on the sp2-conjugated carbon framework, bringing about optimized intermediate adsorption and accelerated electron transfer steps during ORR. In this review, the fundamental chemical and physical properties of nanographenes are first discussed about ORR applications. Afterward, the role of doping, size, defects, and their combined influence in boosting nanographenes' ORR performance is introduced. Finally, significant challenges and essential perspectives of nanographenes as advanced ORR electrocatalysts are highlighted.

Mesoporous silica-modified metal organic frameworks derived bimetallic electrocatalysts for oxygen reduction reaction in microbial fuel cells

The design of cost-effective oxygen reduction reaction (ORR) catalysts in microbial fuel cells (MFCs) remains a challenge. Herein, a mesoporous silica (mSiO2) assisted protection strategy is developed to synthesize highly dispersed CuCo nanoalloys embedded in nitrogen doped carbon Cu/Co-NC@mS catalyst using zeolitic imidazolate framework (ZIF) as carbon and nitrogen sources. The results revealed that the mSiO2 protection holds the potential to inhabit CuCo nanoalloys from aggregation and thus promotes the formation of highly dispersed small CuCo nanoparticles. The obtained catalyst with pyrolysis temperature (T) of 800 °C (Cu/Co-NC@mS-800) achieves the best ORR performance among Cu/Co-NC@mS-T catalysts, yielding a maximum power density of 1000 mW m−2 when employed as air cathode MFCs. The significantly enhanced ORR performance of Cu/Co-NC@mS-800 could be attributed to following aspects: a) highly dispersed small CuCo nanoalloy particles, improved mesoporous surface area and volume owing to mSiO2 protection; (b) the formation of concave regular dodecahedron mesoporous structure with thin graphtic carbon layer as support; (c) the synergetic effect between CuCo nanoalloys. This work provides a facile strategy for the preparation of highly dispersed bimetal nanoalloys with enhanced electrocatalytic performance for energy-related applications.

Three-dimensional nanocomposites derived from combined metal organic frameworks doped with Ce, La, and Cu as a bifunctional electrocatalyst for supercapacitors and oxygen reduction reaction

Fabrication of a nanocomposite with a low-cost and efficient synthesis method instead of using electrocatalysts based on platinum metal has become one of the main challenges in energy storage devices and fuel cells. In this regard, a bifunctional electrocatalyst for supercapacitors and oxygen reduction reaction is fabricated and tested. The novelty of this study is the synthesis method and enhancement of the electrochemical characteristics of synthesized electrocatalysts. The core-shell method is used for the electrocatalyst's synthesis which uses Zeolitic Imidazolate Framework (ZIF)-8, ZIF-67, and Material Institute Lavoisiers (MIL)-101 for the fabrication of three types of electrocatalysts. In the following, to increase the characteristics such as conductivity and stability, doping of Copper (Cu), Cerium (Ce), and Lanthanum (La) are added to the nanocomposites. The Co@NC, CoZn@NC, and CoZn@FeNC prepared electrocatalysts are obtained from the pyrolyze process of La/ZIF-67, CeCu/ZIF-8@ La/ZIF-67, MIL-101@CeCu/ZIF-8/La/ZIF-67. The results indicated that the CoZn@NC electrocatalyst has the best performance in the oxygen reduction reaction (ORR) with an onset potential of 0.062 (V vs Ag/AgCl) and current density of −12.97 (mA/cm2) at a constant voltage of −1 V. Furthermore, the electron transfer number of CoZn@NC electrocatalyst for ORR was 3.64. The conducted Galvanostatic Charge-Discharge (GCD) tests demonstrated that the CoZn@NC electrode has the highest capacitance of 271.14 F/g. The outcomes showed that by the core-shell method, various properties of nanocomposites can be utilized to solve the weaknesses of catalysts by using proper metals. Moreover, the presence of Cu2+,Ce3+,La3+ improve the structural defects in the carbon matrix, the stability based on the chronoamperometry results, and the mass transfer. The study provides a perspective for future researches to fill the research gaps to obtain the new supercapacitors utilize on a large scale in the electronics industry.