Electrocatalysts For Oxygen Reduction Reaction Research Articles

Porphyrin-enhanced microbial fuel cell with PCN-600 electrocatalyst for efficient oxygen reduction reaction and eco-friendly energy generation

Microbial fuel cells (MFCs) stand as a sustainable alternative for wastewater treatment and the production of clean energy. The effectiveness of this technology is intricately linked to the cathodic oxygen reduction reaction (ORR). The exceptional tunability of metal–organic frameworks (MOFs) offers a distinctive platform for customizing their inherent properties, making them promising candidates as new electrocatalysts. In this study, metalloporphyrin MOF (PCN-600) with 1D channels and micro/mesoporous structure was prepared utilizing the preassembled [Fe3O(OOCCH3)6] building blocks. Electrochemical measurements demonstrated the superior ORR performance of PCN-600 compared to bare graphite electrodes, with higher onset and half-wave potentials and enhanced electron transfer rates. PCN-600 exhibited a remarkable 52.72 % improvement in power density (179.43 mW m−2) compared to the control group (MFC-Ctrl, 88.41 mW m−2). Additionally, the chemical oxygen demand (COD) removal efficiency was enhanced, with MFC-PCN-600 achieving 82.58 % COD removal compared to 59.87 % in MFC-Ctrl. The electron-withdrawing N and M−N structure of PCN-600 guarantees an outperforming ORR catalyst toward bioelectricity generation during MFCs performance.

Au enables PdAu aerogel efficient catalysts for oxygen reduction and C2 alcohol oxidation

Metallic aerogels (MAs) with self-supporting three-dimensional (3D) porous structures constitute a potential platform for the construction of robust catalysts. In this work, we successfully constructed 3D PdAu MAs with the optimized d-band electron of Pd and geometrical lattice expansion using a maneuverable in-situ seed-mediated strategy at room temperature. The introduction of Au accelerated the kinetics of Pd4Au3 MAs toward oxygen reduction reaction (ORR), ethylene glycol oxidation reaction (EGOR), and ethanol oxidation reaction (EOR) in alkaline electrolyte, boosting the activity and stability of Pd4Au3 MAs. The mass activities of Pd4Au3 MAs/C in ORR, EGOR and EOR were 1.74, 8.57, and 9.54 A mgPd−1, respectively, which were remarkably better than those of referenced Pd MAs/C, commercial Pt/C and Pd/C. The rotating ring-disk electrode measurement illustrated that Pd4Au3 MAs/C achieved a 4-electron transfer process in ORR from O2 to OH−. In-situ Fourier transform infrared spectroscopy revealed that Pd4Au3 MAs/C enabled the cleavage of the C–C bonds, thus accomplishing the C1-complete oxidation of 10-electron ethylene glycol and 12-electron ethanol. This study provides an efficient strategy to fabricate binary non-Pt alloy aerogels as high-performance multifunctional electrocatalysts for ORR, EGOR, and EOR.

Iron-Cobalt Phosphide Encapsulated in a N-Doped Carbon Framework as a Promising Low-Cost Oxygen Reduction Electrocatalyst for Zinc-Air Batteries.

The oxygen reduction reaction (ORR) plays a vital role in many next-generation electrochemical energy conversion and storage devices, motivating the search for low-cost ORR electrocatalysts possessing high activity and excellent durability. In this work, we demonstrate that iron-cobalt phosphide (FeCoP) nanoparticles encapsulated in a N-doped carbon framework (FeCoP@NC) represent a very promising catalyst for the ORR in alkaline media. The core-shell structured FeCoP@NC catalyst offered outstanding ORR activity with a half-wave potential (E1/2) of 0.86 V vs reversible hydrogen electrode (RHE) and excellent stability in a 0.1 M KOH electrolyte, outperforming commercial Pt/C and many recently reported noble-metal-free ORR electrocatalysts. The superiority of FeCoP@NC as an ORR electrocatalyst relative to Pt/C was further verified in prototype zinc-air batteries (ZABs), with the aqueous and flexible ZABs prepared using FeCoP@NC offering excellent stability, impressive open circuit voltages (1.56 and 1.44 V, respectively), and high maximum power densities (183.5 and 69.7 mW cm-2, respectively). Density functional theory calculations revealed that encapsulating FeCoP nanoparticles in N-doped carbon shells resulted in favorable electron penetration effects, which synergistically regulated the adsorption/desorption of ORR intermediates for optimal ORR performance while also boosting the electronic conductivity. Our findings offer valuable new insights for rational design of transition metal phosphide-based catalysts for the ORR and other electrochemical applications.

Electronic-Structure-Modulated Cu,Co-Coanchored N-Doped Nanocarbon as a Difunctional Electrocatalyst for Hydrogen Evolution and Oxygen Reduction Reactions.

To alleviate the problems of environmental pollution and energy crisis, aggressive development of clean and alternative energy technologies, in particular, water splitting, metal-air batteries, and fuel cells involving two key half reactions comprising hydrogen evolution reaction (HER) and oxygen reduction (ORR), is crucial. In this work, an innovative hybrid comprising heterogeneous Cu/Co bimetallic nanoparticles homogeneously dispersed on a nitrogen-doped carbon layer (Cu/Co/NC) was constructed as a bifunctional electrocatalyst toward HER and ORR via a hydrothermal reaction along with post-solid-phase sintering technique. Thanks to the interfacial coupling and electronic synergism between the Cu and Co bimetallic nanoparticles, the Cu/Co/NC catalyst showed improved catalytic ORR activity with a half-wave potential of 0.865 V and an excellent stability of more than 30 h, even compared to 20 wt% Pt/C. The Cu/Co/NC catalyst also exhibited excellent HER catalytic performance with an overpotential of below 149 mV at 10 mA/cm2 and long-term operation for over 30 h.

Controlled synthesis of nickel phosphides: Mechanistic insights and catalytic activity in hydrogen peroxide production

Strategically designing oxygen reduction reaction (ORR) electrocatalysts based on electronic structure is a pivotal method for enhancing the electrocatalytic activity and selectivity of two-electron (2e) reactions. While many transition metal phosphides, including NixPy, have demonstrated activity in electrocatalytic reactions, their effectiveness in 2e ORR electrocatalysis is still uncertain. In this study, guided by the theoretical insights into high electroactivity unveiled by the d-band center (Ed) theory, we engineered and synthesized Ni2P/Ni5P4 nanosheets (NSs). Functioning as 2e ORR electrocatalysts in alkaline environments, the Ni2P/Ni5P4 NSs exhibited outstanding 2e selectivity of up to 95%, with an electron transfer number close to two. Demonstrating a Faradaic efficiency exceeding 95% over a wide potential range (0.2–0.5 V), these NSs displayed extended stability for over 48 h, outperforming most transition metal-based catalysts reported in literature. By employing density functional theory (DFT) calculations, the increased activity is ascribed to the adjustment of the d-band center at the engineered heterostructure interface, effectively regulating the adsorption energy of oxygen-containing intermediates (*OOH). This study offers crucial insights into the methodical design and production of effective transition metal phosphide electrocatalysts guided by the d-band center theory.

Theoretical investigation of electrocatalytic activity of Pt-free dual atom-doped graphene for O2 reduction in an alkaline solution

Non-precious electrocatalysts as the alternative to Pt have become a hot research area in the last decade due to the suitable catalytic activity in Oxygen reduction reaction (ORR) in electrochemical systems. In this work, the density functional theory calculations were investigated to explore the activity of Fe, Cu, and Fe-Cu atoms supported by N-doped graphene as the ORR electrocatalyst for Oxygen-depolarized cathodes (ODCs). To this end, the ORR mechanism was surveyed in detail in the gas and solvent phases. The results show that the solvent phase leads to a higher overpotential and thermodynamic limiting potential. According to the density of states curves, there are strong interactions between metal atom and substrate that can effectively tune the electronics of catalysts. Bader's analysis confirms that, in addition to the single metal atoms, nitrogen atoms have also played a critical role in charge transfer between substrates and oxygen molecules in ORR. It is also predicted that Fe-Cu@NC SAC exhibits the highest catalytic activity which is consistent with thermodynamic limiting potential and theoretical overpotential of − 0.26 and 0.66 (V vs. SHE), respectively, indicating that this type of catalyst may be a suitable candidate instead of precious metals in oxygen-depolarized cathodes in electrochemical devices.

Synthesis of High-Entropy Perovskite Hydroxides as Bifunctional Electrocatalysts for Oxygen Evolution Reaction and Oxygen Reduction Reaction.

Oxygen reduction reaction (ORR) and oxygen evolutionc reaction (OER) are important chemical reactions for a rechargeable lithium-oxygen battery (LOB). Recently, high-entropy alloys and oxides have attracted much attention because they showed good electrocatalytic performance for oxygen evolution reaction (OER) and/or oxygen reduction reaction (ORR). In this study, we aimed to synthesize and characterize CoSn(OH)6 and two types of high-entropy perovskite hydroxides, that is, (Co0.2Cu0.2Fe0.2Mn0.2Mg0.2)Sn(OH)6 (CCFMMSOH) and (Co0.2Cu0.2Fe0.2Mn0.2Ni0.2)Sn(OH)6 (CCFMNSOH). TEM observation and XRD measurements revealed that the high-entropy hydroxides CCFMMSOH and CCFMNSOH had cubic crystals with sides of approximately 150-200 nm and crystal structures similar to those of perovskite-type CSOH. LSV measurement results showed that the high-entropy hydroxides CCFMMSOH and CCFMNSOH showed bifunctional catalytic functions for the ORR and OER. CCFMNSOH showed better catalytic performance than CCFMMSOH.

Study of the Suitability of Corncob Biochar as Electrocatalyst for Zn–Air Batteries

There has been a recent increasing interest in Zn–air batteries as an alternative to Li-ion batteries. Zn–air batteries possess some significant advantages; however, there are still problems to solve, especially related to the tuning of the properties of the air–cathode which should carry an inexpensive but efficient bifunctional oxygen reduction (ORR) and oxygen evolution (OER) reaction electrocatalyst. Biochar can be an alternative, since it is a material of low cost, it exhibits electric conductivity, and it can be used as support for transition metal ions. Although there is a significant number of publications on biochars, there is a lack of data about biochar from raw biomass rich in hemicellulose, and biochar with a small number of heteroatoms, in order to report the pristine activity of the carbon phase. In this work, activated biochar has been made by using corncobs. The biomass was first dried and minced into small pieces and pyrolyzed. Then, it was mixed with KOH and pyrolyzed for a second time. The final product was characterized by various techniques and its electroactivity as a cathode was determined. Physicochemical characterization revealed that the biochar had a hierarchical pore structure, moderate surface area of 92 m2 g−1, carbon phase with a relatively low sp2/sp3 ratio close to one, and a limited amount of N and S, but a high number of oxygen groups. The graphitization was not complete while the biochar had an ordered structure and contained significant O species. This biochar was used as an electrocatalyst for ORR and OER in Zn–air batteries where it demonstrated a satisfactory performance. More specifically, it reached an open-circuit voltage of about 1.4 V, which was stable over a period of several hours, with a short-circuit current density of 142 mA cm−2 and a maximum power density of 55 mW cm−2. Charge–discharge cycling of the battery was achieved between 1.2 and 2.1 V for a constant current of 10 mA. These data show that corncob biochar demonstrated good performance as an electrocatalyst in Zn–air batteries, despite its low specific surface and low sp2/sp3 ratio, owing to its rich oxygen sites, thus showing that electrocatalysis is a complex phenomenon and can be served by biochars of various origins.

Advanced electrocatalysts for fuel cells: Evolution of active sites and synergistic properties of catalysts and carrier materials

AbstractProton exchange‐membrane fuel cell (PEMFC) is a clean and efficient type of energy storage device. However, the sluggish reaction rate of the cathode oxygen reduction reaction (ORR) has been a significant problem in its development. This review reports the recent progress of advanced electrocatalysts focusing on the interface/surface electronic structure and exploring the synergistic relationship of precious‐based and non‐precious metal‐based catalysts and support materials. The support materials contain non‐metal (C/N/Si, etc.) and metal‐based structures, which have demonstrated a crucial role in the synergistic enhancement of electrocatalytic properties, especially for high‐temperature fuel cell systems. To improve the strong interaction, some exciting synergistic strategies by doping and coating heterogeneous elements or connecting polymeric ligands containing carbon and nitrogen were also shown herein. Besides the typical role of the crystal surface, phase structure, lattice strain, etc., the evolution of structure‐performance relations was also highlighted in real‐time tests. The advanced in situ characterization techniques were also reviewed to emphasize the accurate structure‐performance relations. Finally, the challenge and prospect for developing the ORR electrocatalysts were concluded for commercial applications in low‐ and high‐temperature fuel cell systems.

Rational design of Fe, N co-doped porous carbon derived from conjugated microporous polymer as an electrocatalytic platform for oxygen reduction reaction

Porous iron–nitrogen-doped carbons (FeNC) offer a great platform for construction of cathodic oxygen reduction reaction (ORR) catalysts in fuel cells. However, challenges still remain regarding with the collapse of carbon-skeleton during pyrolysis, uneven distribution of active sites and aggregation of metal atoms. In this work, we synthesized Fe, N co-doped conjugated microporous polymer (FeN-CMP) through a facile bottom-up strategy using 1,3,5-triethynylbenzene and iron-chelated 3,8-dibromo-1,10-phenanthroline as monomers, ensuring the uniform coordination of N with Fe element in network. Then, the resulting FeN-CMP was treated by pyrolysis without structural collapse to obtain porous FeNC electrocatalyst for ORR. The most active catalyst was fabricated under 900 °C, which exhibits remarkable ORR activity in alkaline medium with half-wave potential of 0.796 V (18 mV and 105 mV positive deviation from the commercial Pt/C catalyst and post-doping catalyst), high selectivity with nearly 4e- transfer process and excellent methanol tolerance. Our study first developed porous FeNC electrocatalysts derived from Fe, N-anchoring CMPs based on pre-functionalization of monomers, which exhibits great potential as an alternative to commercial Pt/C catalyst for ORR, and provides a feasible strategy of developing multi-atoms doping catalysts for energy storage and conversion as well as heterogeneous catalysis.

Recent Progress and Prospects of Manganese–Nitrogen–Carbon Electrocatalysts for Oxygen Reduction Reaction

Recent Progress and Prospects of Manganese–Nitrogen–Carbon Electrocatalysts for Oxygen Reduction Reaction

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.

Investigation of phosphoric acid influence on the oxygen reduction reaction on carbon-supported platinum electrocatalyst via rotating disk electrodes

Phosphoric acid (PA), utilized as an electrolyte in high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs), has been observed to exert a detrimental effect on oxygen reduction reaction (ORR) electrocatalyst, consequently compromising cell performance. To comprehensively elucidate the impact of phosphoric acid on ORR, this study employs a range of electrochemical techniques, including electrochemical impedance spectroscopy and voltammetry method. The negative influence of PA on commercial Pt/C electrocatalyst manifests differently under various potentials and PA concentrations. Upon the introduction of PA, the decay rate and amplitude of ECSA, as calculated by Hupd adatoms, are notably smaller compared to the kinetic current density generated by the oxygen reduction reaction. Particularly, in the kinetic-controlled potential range, the negative impact of PA becomes more pronounced at higher electrode potentials, accompanied by a significantly steeper Tafel slope. Additionally, the EIS results suggest that phosphoric acid may gradually transform into polyphosphoric acid at a high concentration, accentuating the poisoning effect of PA under steady-state conditions. However, a high PA concentration can substantially alter the electrolyte properties, potentially leading to an inaccurate assessment of PA tolerance in electrocatalysts. Hence, it is imperative to consider the appropriate PA concentration when evaluating PA tolerance and to discern the poisoning mechanism under different electrode potentials.

One-step hydrothermal synthesis of Pt and N-doped carbon quantum dots co-activated as novel electrocatalysts for oxygen reduction reaction

Abstract In this paper, a novel nano-electrocatalyst (Pt@N-CDs/RGO) with reduced graphene oxide as the carrier and platinum (Pt) and nitrogen-doped carbon quantum dots (N-CDs) together as the active sites was prepared by a simple hydrothermal method. By comparing the electrochemical properties of commercial platinum carbon (Pt/C) and Pt@N-CDs/RGO at 20% wt Pt, it was found that Pt@N-CDs/RGO exhibited excellent ORR properties, such as an onset potential (Eonest ) of 1.10 V, a half-wave potential (E1/2) of 0.82 V, a limiting current density of 5.06 mA/cm2, and a number of transferred electrons as high as 3.97. By using the chronoamperometric method (CA) to cycle for 10000 s, it was found that the stability of both, Pt@N-CDs /RGO maintains 18% activity after a cycle of 10000 seconds, which is much higher than Pt/C. The study showcased a new efficient and durable catalyst for PEMFCs.

Epitaxial growth of Pd clusters on N-doped Ag nanowires for oxygen reduction reaction

Efficient and stable Pt-free electrocatalysts for oxygen reduction reaction (ORR) are indispensable for future fuel cells. Herein, we describe a heterostructure of Pd nanocrystals (PdNCs) on N-doped Ag nanowires (NWs) synthesized using a direct epitaxial growth strategy with a Pd loading of only 9.5 wt.%. The PdAg bimetallic heterostructure showed the highest mass activity among reported PdAg-based ORR electrocatalysts and exhibited excellent stability, with only a 1.5 mV decay in the half-wave potential even after 20000 cycles of continuous testing. The remarkably enhanced activity and durability can be attributed to the distinct advantages of the ultrasmall PdNCs, cocatalysts of N-doped AgNWs, and their heterointerfaces. This work reveals that the epitaxial growth of a heterostructure on a stable support is a promising strategy for promoting catalytic performance.

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.

A first-principles study of the oxygen reduction reaction activity of Pt with TM-N-C support

Developing highly active oxygen reduction reaction (ORR) electrocatalysts is of great significance for energy storage and conversion. In this study, we systematically investigated the effect of transition metal and nitrogen co-doped carbon (TM-N-C) as active support on ORR of Pt by density functional theory (DFT) calculations. Pt with TM-N-C supports (Pt/TM-SACs) exhibited enhanced ORR activity than Pt supported on carbon (Pt/C). The superior ORR activity is attributed to the TM-Nx structure, which can regulate the electronic structure of Pt. Moreover, the coordinated N is significantly correlated with the interaction between Pt and TM-N-C support. These findings provide insights for further exploration of ORR catalysts with active support.

Fullerene-metalloporphyrin co-crystal as efficient oxygen reduction reaction electrocatalyst precursor for Zn-air batteries

Fullerene-metalloporphyrin co-crystal as efficient oxygen reduction reaction electrocatalyst precursor for Zn-air batteries

Elaborate construction of honeycomb-like porous carbon with embedment of N-doped carbon nanotubes as efficient electrocatalyst for zinc-air battery

Devising the synthesis strategy and uncovering the evolution mechanism of carbon-based materials are critical to the development of efficient oxygen reduction reaction (ORR) electrocatalysts for renewable energy storage systems. This study reports a hierarchical ORR electrocatalyst, Co@N-CNTs/3DHC, which features ultrafine cobalt nanoparticles embedded in nitrogen-doped carbon nanotubes (Co@N-CNTs) and Co@N-CNTs firmly anchored in the nano-chambers of a three-dimensional honeycomb-like porous carbon (3DHC). The synthesis strategy of Co@N-CNTs/3DHC involves the initial construction of a precursor, followed by controllable pyrolysis step. Based on detailed analysis of both evolved gases and carbonized products of precursors, the evolution mechanism of Co@N-CNTs/3DHC is specifically proposed. Prompted by the electron reconfiguration, extensive reaction interface and fast mass-transfer pathway, the as-synthesized hierarchical Co@N-CNTs/3DHC displays superior ORR activity in alkaline media (0.88 V of half-wave potential) compared to commercial Pt/C. Impressively, zinc-air battery equipped with Co@N-CNTs/3DHC cathode presents outstanding discharge voltage and exceptional stability. This work highlights a unique perspective on the synthesis strategy and growth mechanism of Co@N-CNTs@3DHC toward creation of hierarchical 3D carbon-based composite for advanced electrochemical energy devices.