Electrocatalysts For Oxygen Reduction Reaction Research Articles

Healing the structural defects of spinel MnFe2O4 to enhance the electrocatalytic activity for oxygen reduction reaction

Spinel metal oxides containing Mn, Co, or Fe (AB2O4, A/B = Mn/Fe/Co) are one of the most promising non-Pt electrocatalysts for oxygen reduction reaction (ORR) in alkaline conditions. However, the low conductivity of metal oxides and the poor intrinsic activities of transition metal sites lead to unsatisfactory ORR performance. In this study, eutectic molten salt (EMS) treatment is employed to reconstruct the atomic arrangement of MnFe2O4 electrocatalyst as a prototype for enhancing ORR performance. Comprehensive analyses by using XAFS, soft XAS, XPS, and electrochemical methods reveal that the EMS treatment reduces the oxygen vacancies and spinel inverse in MnFe2O4 effectively, which improves the electric conductivity and increases the population of more catalytically active Mn2+ sites with tetrahedral coordination. Moreover, the enhanced Mn-O interaction after EMS treatment is conducive to the adsorption and activation of O2, which promotes the first electron transfer step (generally considered as the rate-determining step) of the ORR process. As a result, the EMS treated MnFe2O4 catalyst delivers a positive shift of 40 mV in the ORR half-wave potential and a two-fold enhanced mass/specific activity. This work provides a convenient approach to manipulate the atomic architecture and local electronic structure of spinel oxides as ORR electrocatalysts and a comprehensive understanding of the structure-performance relationship from the molecular/atomic scale.

Transition Metal-Based Polyoxometalates for Oxygen Electrode Bifunctional Electrocatalysis

Polyoxometalates (POMs) with transition metals (Co, Cu, Fe, Mn, Ni) of Keggin structure and lamellar-stacked multi-layer morphology were synthesized. They were subsequently explored as bifunctional electrocatalysts for oxygen electrodes, i.e., oxygen reduction (ORR) and evolution (OER) reaction, for aqueous rechargeable metal-air batteries in alkaline media. The lowest Tafel slope (85 mV dec−1) value and the highest OER current density of 93.8 mA cm−2 were obtained for the Fe-POM electrocatalyst. Similar OER electrochemical catalytic activity was noticed for the Co-POM electrocatalyst. This behavior was confirmed by electrochemical impedance spectroscopy, where Fe-POM gave the lowest charge transfer resistance of 3.35 Ω, followed by Co-POM with Rct of 15.04 Ω, during the OER. Additionally, Tafel slope values of 85 and 109 mV dec−1 were calculated for Fe-POM and Co-POM, respectively, during the ORR. The ORR at Fe-POM proceeded by mixed two- and four-electron pathways, while ORR at Co-POM proceeded exclusively by the four-electron pathway. Finally, capacitance studies were conducted on the synthesized POMs.

Preparation and evaluation of S-rGO/ZnFe2O4/NiCoLDH nanocomposite electrocatalyst in oxygen reduction reaction

This study introduces a novel combination of sulfur-doped reduced graphene oxide (S-rGO), zinc ferrite (ZnFe2O4) and nickel cobalt layered double hydroxide (NiCoLDH) as an efficient and low-cost electrocatalyst for oxygen reduction reaction (ORR) for the first time. The hydrothermal method is used to synthesize all samples including graphene oxide (GO), S-rGO, NiCoLDH, ZnFe2O4 and S-rGO/ZnFe2O4/NiCoLDH hybrids. X-ray diffraction (XRD) analysis, field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), energy dispersive x-ray analysis (EDX), electrochemical surface area (ECSA), and fourier transform infrared spectroscopy (FTIR) analysis are used to determine the structure of synthesized electrocatalysts, physical properties, and morphology. The electrochemical measurements are carried out using cyclic voltammetry (CV), linear scanning voltammetry (LSV), chronoamperometry (ChA), and electrochemical impedance spectroscopy (EIS). The results for all samples are compared with the Pt/C commercial catalyst. According to the electrochemical results, the S-rGO/ZnFe2O4/NiCoLDH electrocatalyst has the best electrochemical performance. Moreover, the nanocomposite exhibited better electrocatalysis, a high diffusion limiting current density of −5.4 mA cm−2 and an onset potential of 0.03 V. Based on the results of this study, the LDH enhances electrical conductivity, electrocatalytic activity, active surface area, and stability of the catalyst for ORR after combining with carbon bases and ferrite.

Cu-based active sites supported on nitrogen-rich polymer derived porous carbon fibers as an oxygen reduction electrocatalyst for zinc-air batteries

The rational design of electrocatalysts with highly exposed active sites and maximized active sites utilization is challenging and urgent problem. Herein, a facile strategy is employed to fabricate Cu-based active sites anchored in nitrogen doped porous carbon nanofiber as an effective and enduring oxygen reduction reaction (ORR) electrocatalyst, which is achieved by the coordination-pyrolysis way of the pre-designed covalent organic polymer (COP) precursors with unique molecular structure. Meanwhile, COP-derived N-doped carbon nanofiber could provide porous structure and facilitate the rapid mass/electron transport, which can insure the strong fastness and high reaction activity of Cu-based active sites. The as-obtained catalyst (Cu0·4/NPC) displays excellent activity (E1/2 = 0.845 V) and stability for ORR performance. Remarkably, the Cu0·4/NPC as cathode catalyst assembled Zn-air battery achieves the peak power density of 142 mA cm−2 and a large specific capacity of 829 mA h g−1 at large current. Additionally, the Cu0·4/NPC catalyst assembled in the solid Zn-air battery achieves the peak power density of 157 mA cm−2. This work offers great opportunity to design advanced ORR catalysts with high density and maximum utilization of active sites.

Reactivity and Durability of Covalent Organic Frameworks Derived Co‐based Hybrid Bifunctional Electrocatalysts for Zinc‐Air Batteries

Developing bifunctional non‐precious metal electrocatalysts of superior reactivity and durability is essential. Herein, we report a class of phthalocyanine‐based covalent organic frameworks as self‐sacrificial precursors derived Co‐based hybrid electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The fabricated Co‐COFs/CNT‐700 catalysts displayed highly efficient ORR properties with a half‐potential of 0.83 V, while its half‐wave potential in alkaline solution at a current density of 10 mA cm‐2 is 1.70 V in the OER test, reflecting exceptional OER activity. Moreover, zinc‐air batteries assembled with Co‐COFs/CNT‐700 catalysts exhibit a marginally higher power density (114 mW cm2) than traditional Pt/C‐IrO2 batteries in an air atmosphere, along with an enhanced cycling stability (5.1% potential loss after 65 h). This work may pave a facile and efficient approach for fabricating electrocatalytic materials with controllably introduced metals and heteroatoms.

Hierarchical pore engineering of MOF-5 derived electrocatalysts with high mass transfer for zinc-air flow batteries

From micro to macro level, the performance of zinc-air flow battery (ZAFB) hinges on two crucial factors: the effective oxygen reduction reaction (ORR) electrocatalysts, and the durable triple-phase electrodes. However, sluggish kinetic process always occurs due to insufficient active sites and hysteretic mass transfer. In this work, a well-confined iron phthalocyanine (FePc) structure onto carbonized metal-organic framework (C-MOF5) electrocatalyst is constructed through a pyrolysis-free strategy. The macrocyclic skeleton of MOF-5 has been confirmed to offer a stronger and more abundant environment for hosting FePc molecules. Attributing to the hierarchical pore engineering of MOF-5, the FePc@C-MOF5 electrocatalyst reveals a high content of Fe (5.68 wt%) with multiple exposed active sites. Notably, the FePc@C-MOF5 exhibits a remarkably high half-wave potential of 0.915 V for ORR in 0.1 M KOH, surpassing that of commercial Pt/C by nearly 60 mV. From a higher-level device perspective, the highest oxygen diffusion velocity and local current density of the FePc@C-MOF5 electrode is verified by computational fluid dynamics (CFD) simulations. As a result, the as-assembled ZAFB demonstrates long-term stability with 200 h’ cycling. This work not only presents the hierarchical pore tailoring strategy for designing ORR electrocatalysts but also offers a deeper understanding of the essence of interfacial mass transfer.

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.

Progress and Outlook of Carbon-supported Single-atom Electrocatalyst for Oxygen Reduction Reaction

Progress and Outlook of Carbon-supported Single-atom Electrocatalyst for Oxygen Reduction Reaction

Trace copper and bi-nonmetallic (N/S) modified ketjenblack (KB) as advanced electrocatalysts for oxygen reduction reactions

Trace copper and bi-nonmetallic (N/S) modified ketjenblack (KB) as advanced electrocatalysts for oxygen reduction reactions

Upcycling retired Li-ion batteries into high-performance oxygen reduction reaction electrocatalysts in flexible Al-air batteries

Upcycling retired lithium-ion batteries (LIBs) into value-added electrocatalysts represents a promising strategy for tuning the trash into treasure. Herein, an effective approach is reported to convert the LIB anode residues into electrocatalysts that enhance the oxygen reduction reaction (ORR). The residues are utilized for synthesizing reduced graphene oxides (rGO) with Mn nanoparticles anchored by N and S dopants (Mn/NS-rGO). A Pt/C-comparable ORR performance is achieved in alkaline media, with the onset and half-wave potentials of 1.01 and 0.87 V, as well as the excellent durability. Density functional theory (DFT) calculations reveal that Mn sites, coordinating with N and S dopants, simultaneously optimize the intermediate adsorption and charge distribution, which in turn facilitates ORR. The solid-state Al-air batteries are assembled by using Mn/NS-rGO as the cathode catalyst, showing the power density of 103.8 mW cm−2, which successfully charge a cell phone and power LED lights under flexible working conditions.

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.

Preparation and performance of the non-platinum catalyst for oxygen reduction reaction in fuel cells

The oxygen reduction reaction (ORR) of the fuel cells is a core of energy conversion, whereas its kinetics is slow due to the limitation of the activation energy barrier, which dramatically limits the commercial development of fuel cells. At present, the main electrocatalyst for the cathode oxygen reduction reaction of fuel cells is the platinum (Pt)-based catalyst. Still, as a precious metal, Pt has a high price, low reserves, and poor stability. These shortcomings seriously affect the mass production and commercialization of fuel cells. Therefore, there is an urgent need for the development of fuel cells to study a low price, sufficient production, high stability, and pollution-free non-Pt catalyst. The main research content of this paper is to use biomass sycamore ball as a carbon source, mixed with ferric chloride (III) hexahydrate and melamine, and prepare the carbon, nitrogen, and iron co-doped ORR catalyst by high-temperature calcination under a nitrogen atmosphere. The physical characterization and electrochemical testing of the obtained samples were conducted at room temperature. The results showed that the pretreatment of sycamore ball powder to iron ratio of 1:3 had the best catalytic performance.

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.

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.