Oxygen Reduction Electrocatalysts Research Articles

In-situ construction of 2D β-Co(OH)2 nanosheets hybridized with 1D N-doped carbon nanotubes as efficient bifunctional electrocatalyst for oxygen reduction and evolution reactions

In-situ construction of 2D β-Co(OH)2 nanosheets hybridized with 1D N-doped carbon nanotubes as efficient bifunctional electrocatalyst for oxygen reduction and evolution reactions

The preparation of Fe, N Co-doped ZIF-derived carbon nanosheet catalysts for oxygen reduction electrocatalyst in zinc-air batteries

A co-doping approach involving transition metals and heteroatoms was employed to successfully synthesize carbon nanosheet catalysts co-doped with iron (Fe) and nitrogen (N). Employing ferrous sulfate as the Fe source, ZIF-8 as the carbon substrate, 1,10-phenanthroline as the metal chelating agent and nitrogen source, Fe2+ can automatically adhere to the ZIF-8 N-doped carbon nanosheets under the chelation of 1,10-phenanthroline. After pyrolysis, Fe is successfully incorporated into the carbon matrix, the generation of numerous ORR active sites, Fe-Nx, are formed, enhancing the ORR catalytic efficiency. In alkaline solutions, the synthesized Fe-NCF-2 catalyst exhibits excellent ORR electrocatalytic activity compared to commercial Pt/C (20 wt% Pt). The ZAB assembled with Fe-NCF-2 as the air cathode demonstrates outstanding performance. This provides an economically viable preparation strategy for exploring efficient catalysts for the ORR.

Comparison of cost and performance between traditional and green processes for producing bimetallic carbide based oxygen reduction electrocatalysts

Chemical (ion exchange resin) and biomass (water hyacinth leaves) as carbon precursors are adopted to prepare two kinds of bimetallic carbide (Fe2MoC)-based catalytic materials. It is found that, compared with the material that use ion-exchange resin as carbon precursor (N-Fe2MoC-RG), the material that use water hyacinth as carbon precursor (N-Fe2MoC-WHG) has more advantages in cost, environment protection, synthesis simplicity, and catalytic activity for oxygen reduction reaction (ORR). Therein, the N-Fe2MoC-WHG as a cathode catalyst displays a half-wave potential of 0.905 V (vs. RHE) for catalyzing ORR in alkaline media, and gets a high peak power density of 1.52 W cm-2 in alkaline electrolyte membrane fuel cell; moreover, the N-Fe2MoC-WHG displays higher power-density retention or growth rate at lower relative humidity, higher back pressure, higher working temperature and higher catalyst loading, compared with the N-Fe2MoC-RG. The N-Fe2MoC-WHG is one of the most active precious metal-free catalysts reported so far, and its stability is very excellent.

Efficient nano-size ZnM/rGO (M = Ni, Cu, and Fe) electrocatalysts for oxygen electrode reactions in alkaline media

Herein, zinc with nickel, copper, and iron was deposited on reduced graphene oxide (rGO) (ZnM/rGO, M = Cu, Ni, Fe) and examined as novel bifunctional electrocatalysts for oxygen evolution (OER) and oxygen reduction (ORR) reaction in alkaline media. Fourier-transform infrared and X-ray photoelectron spectroscopy, X-ray powder diffraction analysis, transmission, and scanning electron microscopy with energy-dispersive X-ray spectroscopy were used for the examination of structural and morphological properties of ZnM/rGO. ZnFe/rGO showed the lowest OER overpotential and Tafel slope, the highest OER current density with the lowest charge-transfer resistance. Furthermore, ORR at ZnFe/rGO proceeds by mixed 2e/4e mechanism, and by 2e mechanism at the other materials. Still, ZnCu/rGO showed the most positive onset potential and low Tafel slope during ORR. Hence, ZnFe/rGO presents the best OER activity with further improvements needed in terms of its ORR performance to reach full potential for rechargeable metal-air batteries and unitized regenerative fuel cells.

Black phosphorus nanodots-modified Pt/C electrocatalyst for methanol-tolerant oxygen reduction in direct methanol fuel cells

Black phosphorus nanodots-modified Pt/C electrocatalyst for methanol-tolerant oxygen reduction in direct methanol fuel cells

Enabling High‐Rate and Long‐Cycling Zinc–Air Batteries with a ΔE = 0.56 V Bifunctional Oxygen Electrocatalyst

AbstractZn–air batteries (ZABs) are promising next‐generation energy storage devices due to their low cost, intrinsic safety, and environmental benignity. However, the sluggish kinetics of the cathodic reactions severely limits the ZAB performances in practical use, calling for high‐efficiency bifunctional oxygen reduction and evolution electrocatalysts. Herein, an ultrahigh‐active bifunctional electrocatalyst is developed with a record‐low ΔE of 0.56 V, significantly outperforming the noble‐metal‐based benchmark (Pt/C+Ir/C, ΔE = 0.77 V) and many other reported bifunctional electrocatalysts (mostly ΔE ≥ 0.60 V). The nanoscale composite of Fe‐based single‐atom sites and nanosized layered double hydroxides endows the bifunctional electrocatalyst with high conductivity and a large active surface that afford strengthened electron conduction and ion transport pathways. Furthermore, a remarkable improvement in stability is realized following the current division principle. ZABs with the bifunctional electrocatalyst deliver a high peak power density of 198 mW cm−2 and excellent cycling durability for over 6000 cycles. Moreover, ampere‐hour‐scale ZABs are constructed and cycled under 1.0 A and 1.0 Ah conditions. This work breaks the activity record for bifunctional oxygen electrocatalysis and expands the potential of ZABs for sustainable energy storage.

Resolving optimal ionomer interaction in fuel cell electrodes via operando X-ray absorption spectroscopy

To bridge the gap between oxygen reduction electrocatalysts development and their implementation in real proton exchange membrane fuel cell electrodes, an important aspect to be understood is the interaction between the carbon support, the active sites, and the proton conductive ionomer as it greatly affects the local transportations to the catalyst surface. Here we show that three Pt/C catalysts, synthesized using the polyol method with different carbon supports (low surface area Vulcan, high surface area Ketjenblack, and biomass-derived highly ordered mesoporous carbon), revealed significant variations in ionomer-catalyst interactions. The Pt/C catalysts supported on ordered mesoporous carbon derived from biomass showed the best performance under the gas diffusion electrode configuration. Through a unique approach of operando X-ray Absorption Spectroscopy combined with gas sorption analysis, we were able to demonstrate the beneficial effect of mesopore presence for optimal ionomer-catalyst interaction at both molecular and structural level.

Wet-chemical synthesis of Co3Mo3C-based electrocatalysts for oxygen reduction and evolution reactions

Abstract In recent years, efforts have been made to adapt secondary metal–air batteries for practical rechargeable applications through the development of bifunctional catalysts, which are highly active in both oxygen reduction reaction and oxygen evolution reaction. Molybdenum carbides, known for their high chemical durability and electrical conductivity, are being investigated as electrode materials for hydrogen evolution reactions in water electrolysis. In this study, we found a new wet chemical synthesis of cobalt-molybdenum-based carbides. Especially, the synthesized Mn-doped Co₃(Mo₀.₉Mn₀.₁)₃C catalyst gave a remarkable activity for both oxygen evolution reaction and oxygen reduction reaction, showing significant potential for the advancement of metal–air batteries as secondary batteries.

Cobalt Nitride-Implanted PtCo Intermetallic Nanocatalysts for Ultrahigh Fuel Cell Cathode Performance.

Stable and active oxygen reduction electrocatalysts are essential for practical fuel cells. Herein, we report a novel class of highly ordered platinum-cobalt (Pt-Co) alloys embedded with cobalt nitride. The intermetallic core-shell catalyst demonstrates an initial mass activity of 0.88 A mgPt-1 at 0.9 V with 71% retention after 30,000 potential cycles of an aggressive square-wave accelerated durability test and loses only 9% of its electrochemical surface area, far exceeding the US Department of Energy 2025 targets, with unprecedented stability and only a minimal voltage loss under practical fuel cell operating conditions. We discover that regulating the atomic ordering in the core results in an optimal lattice configuration that accelerates the oxygen reduction kinetics. The presence of cobalt nitride decorated within PtCo superlattices guarantees a larger barrier to Co dissolution, leading to the excellent endurance of the electrocatalysts. This work brings up a transformative structural engineering strategy for rationally designing high-performing Pt-based catalysts with a unique atomic configuration for broad practical uses in energy conversion technology.

Mechanistic Study of Highly Active Bifunctional Double-Atom Electrocatalysts for Oxygen Reduction and Oxygen Evolution Reactions.

Dual-atom catalysts (DACs) can be very effective for catalyzing both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, we present theoretical evidence of a new class of highly active DACs, namely, the double-atom embedded in nitrogen-doped graphene sheet 2M-N-C (M = Mn, Fe) on the basis of density functional theory calculations. Importantly, we find that the double active sites of 2M-N-C DACs entail an unconventional catalytic reaction pathway for ORR and OER. We also show that the local coordination environment of the active sites can significantly affect the stability and oxygen catalytic activity of 2M-N-C DACs. In particular, MnFe-N-C DAC not only exhibits good stability but also possesses outstanding bifunctional ORR/OER catalytic activity with the potential difference (ΔE) between the OER and ORR as low as 0.34 V, notably lower than most bifunctional electrocatalysts reported in the literature. This finding suggests a new strategy toward the design of stable and highly active bifunctional electrocatalysts for both ORR/OER.

Constructing Dual-Phase Co9S8-CoMo2S4 Heterostructure as an Efficient Trifunctional Electrocatalyst for Oxygen Reduction, Oxygen Evolution and Hydrogen Evolution Reactions.

Designing robust, efficient and inexpensive trifunctional electrocatalysts for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is significant for rechargeable zinc-air batteries and water-splitting devices. To this end, constructing heterogenous structures based on transition metals stands out as an effective strategy. Herein, a dual-phase Co9S8-CoMo2S4 heterostructure grown on porous N, S-codoped carbon substrate (Co9S8-CoMo2S4/NSC) via a one-pot synthesis is investigated as the trifunctional ORR/OER/HER electrocatalyst. The optimized Co9S8-CoMo2S4/NSC2 exhibits that ORR has a half-wave potential of 0.86 V (vs. RHE) and the overpotentials at 10 mA cm-2 for OER and HER are 280 and 89 mV, respectively, superior to most transition-metal based trifunctional electrocatalysts reported to date. The Co9S8-CoMo2S4/NSC2-based zinc-air battery (ZAB) has a high open-circuit voltage (1.41 V), large capacity (804 mAh g-1) and highly stable cyclability (97 h at 10 mA cm-2). In addition, the prepared Co9S8-CoMo2S4/NSC2-based ZAB in series can self-drive the corresponding water-splitting device. The dual-phase Co9S8-CoMo2S4 heterostructure provides not only multi-type active sites to drive the ORR, OER and HER, but also high-speed charge transfer channels between two phases to improve the synergistic effect and reaction kinetics.

Bamboo-like nitrogen-doped carbon nanotubes directly grown from commercial carbon black for encapsulating FeCo nanoparticles as efficient oxygen reduction electrocatalysts

Efficient methods for preparing carbon nanotube (CNT)-confined metal catalysts are of great significance for electrocatalysis. Hence, in this study, Fe and Co promoters were added to the precursors of commercial carbon black and melamine to form N-doped CNTs confined bimetallic catalysts (FeCo@N-CNTs) via in situ pyrolysis. The FeCo@N-CNT catalysts exhibited a bamboo-like morphology with FeCo alloy nanoparticles encapsulated in the CNTs and high activity toward the oxygen reduction reaction, with a half-wave potential of 0.864 mV, higher than that of commercial Pt/C (0.827 mV) in alkaline solutions. The catalytic performance is attributable to the synergistic effects between the FeCo alloy and N-doped CNT structure. Moreover, the confinement of the FeCo nanoparticles inside the CNTs imparted the prepared catalysts with resistance to methanol poisoning and long-term stability. This versatile method of synthesizing CNTs directly from carbon black provides a new strategy for preparing high-performance non-precious-metal-based N-doped CNT catalysts for practical fuel cell applications.

Hybrid Nanoalloy‐Cluster‐Single Atom Sites Based Aerophilic Carbon Fiber Membranes as Binder‐Free Cathodes for Ultra‐Long‐Life Zn‐air Batteries

AbstractHigh‐efficient and durable electrocatalysts for oxygen reduction and oxygen evolution reaction (ORR/OER) are desirable to Zn‐air batteries (ZABs). However, most of catalysts in powder form with sole active sites remain challenging in achieving the satisfactory bifunctional catalysis and suffer from peeling off during the long‐term operation. Herein, hybrid CoFe active sites are constructed containing nanoalloys (≈10 nm), clusters (< 2 nm), and single atoms on aerophilic carbon fiber membranes as binder‐free air cathodes for ultra‐long‐life ZABs. In particular, the high air‐permeability of membranes (0.2 s) can prevent the active sites from blocking by O2 bubbles and promote the mass transfer. The theoretical and experimental results confirm that the hydrophilic CoFe2O4/CoFeOOH sites reconstructed on the surface of CoFe nanoalloys are mainly responsible for OER. While for single atoms and clusters on nitrogen (N)‐doped carbon matrix, they play a synergetic role in optimizing the adsorption energy to enhance ORR activity. Thus, the as‐prepared catalysts exhibit an ultra‐low ORR/OER potential gap (0.64 V). When further assembled as freestanding air‐electrodes, it exhibits an outstanding cycling lifespan of 1200 and 155 h in liquid‐ and quasi‐solid‐state ZABs respectively, which are fivefold and twofold higher than those of powder‐based cathodes (240/67 h).

Manipulation of d-Orbital Electron Configurations in Nonplanar Fe-Based Electrocatalysts for Efficient Oxygen Reduction.

Manipulation of the spin state holds great promise to improve the electrochemical activity of transition metal-based catalysts. However, the underlying relationship between the nonplanar metal coordination environment and spin states remains to be explored. Herein, we report the precise regulation of nonplanar Fe atomic d-orbital energy level into an irregular tetrahedral crystal field configuration by introducing P atoms. With the increase of P coordination number, the spin magnetic moment decreases linearly from 3.8 μB to 0.2 μB, and the high spin content decreases linearly from 31% to 5%. Significantly, a volcanic curve between the spin states of Fe-based catalysts (Fe-NxPy) and oxygen reduction reaction (ORR) activity has been unequivocally established based on the thermodynamic results. Thus, the Fe-N3P1 catalyst with a 19% medium spin state experimentally exhibits the optimal reaction activity with a high half-wave potential of 0.92 V. These findings indicate that regulating electron spin moments through coordination engineering is a promising catalyst design strategy, providing important insights into spin catalysis.

Highly Porous Nitrogen and Phosphorus Dual-Doped Carbon with Increased Phosphorus Content As an Efficient Oxygen Reduction Electrocatalyst

Highly porous nitrogen and phosphorus dual-doped carbon (NPC) was synthesized using acetylene black as a carbon source in two steps: (1) solid–gas mechanochemical treatment to prepare nitrogen-doped carbon (NC), (2) heat treatment to dope the NC with phosphorus. X-ray photoelectron spectroscopy and N2 gas adsorption analysis revealed that the solid–gas mechanochemical treatment using a ball mill incorporated nitrogen atoms into the carbon network and increased the pore volume and surface area. Furthermore, the resulting NC exhibited enhanced reactivity with ammonium dihydrogen phosphate, which was used as a phosphorus source, upon heat treatment. The phosphorus content in NPC synthesized by two-step mechanochemical and heat treatments reached 1.91 at%, a 14-fold increase compared to that of phosphorus-doped carbon synthesized by heat treatment. The NPC exhibited higher electrocatalytic activity for the oxygen reduction reaction than NC, suggesting that the additional phosphorus doping into NC can improve its electrocatalytic performance.

Benchmarking Metal Oxide Electrocatalysts for Oxygen Reduction

Benchmarking Metal Oxide Electrocatalysts for Oxygen Reduction

Boosting the activity of nitrogen-doped carbon catalyst by the guided formation of active sites and enhanced scavenging on reactive oxygen species under the regulation of cerium

The design of nitrogen-doped carbon materials with high density of active sites is of paramount importance for catalysis of the oxygen reduction reaction (ORR). Herein, an efficient oxygen reduction electrocatalyst (CL-Fe/(Fe,Ce)xOy-NC) is developed by planting carbon nanotubes with encapsulated Fe/(Fe,Ce)xOy particles on porous carbon polyhedron particles derived from calcinated ZIF-8 framework. The introduction of Ce evidently promotes the formation of pyridinic nitrogen, graphitic nitrogen and metal nitrogen species in carbon matrix, enhancing the catalytic activity towards the ORR. The Ce oxide in the catalyst effectively scavenges the active oxygen species in ORR process. Under the synergistic effect of high specific surface area with Ce species, the CL-Fe/(Fe,Ce)xOy-NC has a better half-wave potential (0.861 V vs. RHE), faster kinetics (44.13 mV dec−1) and is more stable than the commercial Pt/C catalyst. The zinc-air battery assembled with CL-Fe/(Fe,Ce)xOy-NC has the highest power density of 195 mW cm−2, energy density of 858 Wh kg−1, and better durability. This work presents a novel approach to enhance the efficacy of nitrogen-doped carbon-based catalysts, paving a possible way to substitute the precious platinum catalysts for a variety of electrochemical energy devices.

Spin Manipulation of Heterogeneous Molecular Electrocatalysts by an Integrated Magnetic Field for Efficient Oxygen Redox Reactions.

Understanding the spin-dependent activity of nitrogen-coordinated single metal atom (M-N-C) electrocatalysts for oxygen reduction and evolution reactions (ORR and OER) remains challenging due to the lack of structure-defined catalysts and effective spin manipulation tools. Herein, both challenges using a magnetic field integrated heterogeneous molecular electrocatalyst prepared by anchoring cobalt phthalocyanine (CoPc) deposited carbon black on polymer-protected magnet nanoparticles, are addressed. The built-in magnetic field can shift the Co center from low- to high-spin (HS) state without atomic structure modification, affording one-order higher turnover frequency, a 50% increased H2O2 selectivity for ORR, and a ≈4000% magnetocurrent enhancement for OER. This catalyst can significantly minimize magnet usage, enabling safe and continuous production of a pure H2O2 solution for 100 h from a 100 cm2 electrolyzer. The new strategy demonstrated here also applies to other metal phthalocyanine-based catalysts, offering a universal platform for studying spin-related electrochemical processes.

Machine learning-assisted dual-atom sites design with interpretable descriptors unifying electrocatalytic reactions

Low-cost, efficient catalyst high-throughput screening is crucial for future renewable energy technology. Interpretable machine learning is a powerful method for accelerating catalyst design by extracting physical meaning but faces huge challenges. This paper describes an interpretable descriptor model to unify activity and selectivity prediction for multiple electrocatalytic reactions (i.e., O2/CO2/N2 reduction and O2 evolution reactions), utilizing only easily accessible intrinsic properties. This descriptor, named ARSC, successfully decouples the atomic property (A), reactant (R), synergistic (S), and coordination effects (C) on the d-band shape of dual-atom sites, which is built upon our developed physically meaningful feature engineering and feature selection/sparsification (PFESS) method. Driven by this descriptor, we can rapidly locate optimal catalysts for various products instead of over 50,000 density functional theory calculations. The model’s universality has been validated by abundant reported works and subsequent experiments, where Co-Co/Ir-Qv3 are identified as optimal bifunctional oxygen reduction and evolution electrocatalysts. This work opens the avenue for intelligent catalyst design in high-dimensional systems linked with physical insights.

In situ green architecture of the 3D FeZn-N-C based electrocatalyst for efficient oxygen reduction.

We prepared a 3D FeZn-N-C based catalyst by green in situ growth of 1D Fe-N-C carbon nanotubes by introducing ferrocyanide ions on the surface of 2D exfoliated MOF-5. The 1D/2D FeZn-N-C based electrocatalyst is conducive to O2 diffusion and ionic/electron transfer, exhibiting an excellent ORR catalytic performance and a peak power density of 294 mW cm-2 for Zn-air batteries.