Oxygen Reduction Electrocatalysts Research Articles

Carbon-Encapsulated Cobalt Phosphide Nanowires as Trifunctional Catalysts for Water Splitting Devices

Cobalt-based catalysts have been widely proved to be promising electrocatalysts for oxygen reduction (ORR), hydrogen evolution (HER), and oxygen evolution (OER). In this paper, to maximize the trifunctional reactivity of the catalyst, a series of one-dimensional carbon-coated cobalt-based compound nanowires with changed anions were reported, and their trifunctional activities were systematically investigated. Among the cobalt-based compounds with different anions, carbon-encapsulated cobalt phosphide nanowires (CoP/C NWs) show impressive trifunctional catalytic activity toward ORR, OER, and HER. Using CoP/C NWs as a trifunctional electrocatalyst, an integrated device of the two-electrode water splitting device powered by the zinc–air battery system was realized. The assembled zinc–air battery exhibits high power density (115 mW cm–2) and long-term cycle stability (over 350 h, 1050 cycles). This work provides an insight into the effects of anion substitution on electrocatalytic activity and provides a highly effective feasibility for the design of energy-related devices with high-activity and durable catalysts.

Electronic Modulation of Pd/C by Simultaneous Doping of Cu and Co Tendering a Highly Durable and Methanol-Tolerant Oxygen Reduction Electrocatalyst

Pd-based electrocatalysts are considered as suitable replacement for Pt-based ones owing to the similar electronic structure of Pd, relatively low cost, and superior catalytic performance. The activity and utilization efficiency of Pd in electrochemical reactions can be increased by alloying with transition metals, like Cu and Co. Herein, we report the synthesis of a homogeneously embedded Pd2CuCo alloy in the carbon matrix. Compared with the benchmark Pt/C, the as-synthesized Pd alloy electrocatalyst exhibited an improved limiting current density (Jm; −5.65 mA cm–2), a smaller Tafel slope (58.7 mV dec–1), and a comparable onset potential (Eonset; 0.91 V vs RHE). Comparatively, the optimized Pd2CuCo showed a current retention of ∼96% after a 6 h stability test and only a 4 mV loss in the half-wave potential (E1/2) after 10,000 redox cycles, while Pt/C showed a current retention of 72.5% and a loss of 5 mV in E1/2. Meanwhile, the Pd2CuCo alloy electrocatalyst also demonstrated excellent methanol tolerance compared to benchmark Pt/C. In addition, the electrocatalyst showed higher activity and long-term stability toward the formic acid oxidation reaction than Pd/C, signifying the potential for wide applicability.

Pd@PtRuNi core–shell nanowires as oxygen reduction electrocatalysts

Fuel cells, as the alternative to fossil energy, have engaged widespread attention by reason of the high conversion efficiency from the chemical energy to the electric energy combined with low pollution emissions. The cathodic ORR catalysts with excellent performance and cost-effectiveness are the dominant point towards the massive development of fuel cells. Here, our group select the Pd NWs as the template and construct the Pd@PtRuNi core–shell bilayer nanostructure to expand platinum atom utilization. Pd@PtRuNi bilayer core–shell NWs unfold elevated mass activity of at 0.9 V versus RHE in alkaline media, 2.03- and 6.23-fold of pristine Pd NWs and benchmark commercial Pt/C, respectively. Meanwhile, the cyclic stability tests reveal the excellent durability of Pd@PtRuNi NWs, whose mass activity is only 13.58% degradation after accelerated durability tests. The catalytic activity and durability towards ORR are better than the U.S. 2025 DOE target ( and less than 40% activity attenuation at 0.9 V after 30 000 potential cycles). The elevated catalytic properties can be traceable to the synergism between the ligand effect of Ni and Ru and one-dimensional structure superiority, which optimizes the electronic structure of active sites, promotes the charge transfer and restrains the agglomeration and detachment.

MOF-Conductive Polymer Composite Film as Electrocatalyst for Oxygen Reduction in Acidic Media

A metal-organic framework (MOF)-conductive polymer composite film was constructed from PCN-222(Fe) nanoparticles and PEDOT:PSS solution by simple drop-casting approach. The composite film was tested as an electrocatalytic device for oxygen reduction reaction (ORR). The combination of PCN-222(Fe) MOF particles and conductive PEDOT matrix facilitates electron transfer in the composite material and improves the ORR performance of PCN-222(Fe). Levich plot and H2O2 quantification experiment show that PCN-222(Fe)/PEDOT:PSS film mainly catalyzes two-electron oxygen reduction and produces H2O2.

Tuning the activity of cobalt 2-hydroxyphosphonoacetates-derived electrocatalysts for water splitting and oxygen reduction: Insights into the local order by pair distribution function analysis

Pyrophosphate- or phosphide-based iron/cobalt electrocatalysts were prepared from the metal (R,S)−2-hydroxyphosphonoacetates to evaluate the effects of metal composition, N-doping and P-enrichment on the electrocatalytic activity. Rietveld and Pair Distribution Function analysis were used to determine phase composition. Irrespectively of the amorphous or crystalline nature, all pyrolyzed solids transformed under OER operation into biphasic Fe/CoO(OH), composed of discrete clusters (size ≤ 20 Å). Carbon paper-supported Fe0.2Co0.8O(OH) electrocatalysts displayed the best OER performances (overpotentials of 270–279 mV at 10 mA·cm−2), attributable to the formation of highly active bimetallic intermediate species. For HER, increased concentration of o-CoP in phosphide-based electrocatalysts resulted in improved performance, up to an overpotential of 140 mV. Employed as anode in alkaline water splitting, amorphous Fe-doped cobalt pyrophosphate and phosphide-derived electrocatalysts showed a cell voltage of 1.58 V at 10 mA·cm−2, with comparable stability to that of RuO2 and requiring lower voltage demand at high current densities.

Three-Dimensional Fe-N-C-Supported Amorphous NiFe alloy Nanoparticles as an Efficient Bifunctional Electrocatalyst for Zn-Air Batteries

The development of highly active and durable bifunctional oxygen reduction and evolution reaction (OER/ORR) electrocatalysts is vitally important for rechargeable metal-air batteries. However, little research has been done on the development of amorphous materials as bifunctional catalysts. Here, amorphous NiFe alloy nanoparticles (a-NiFe) coupled to transition metal nitrogen-doped carbon (Fe-N-C) substrate (a-NiFe@Fe-N-C) have been produced and ducted by a simple synthesis method. It is confirmed that the a-NiFe@Fe-N-C composite has significant amorphous characteristics according to XRD, HR-TEM, and SAED characterization methods, and the amorphous structure has abundant defects caused by the disordered arrangement of atoms, which is conducive to accommodate a large mass of active sites and promote the performance of catalysts. Additionally, the large specific surface area, the interconnected multistage pore structure, and the superior electrical conductivity of the Fe-N-C substrate, as well as the synergistic effect between bimetals Ni and Fe, make a-NiFe@Fe-N-C composite electrocatalyst present superior bifunctional catalytic activity and durability. Remarkably, compared with benchmark Pt/C + IrO2, the rechargeable liquid Zinc-air battery using a-NiFe@Fe-N-C as cathode exhibits a superior power density (170 mW·cm−2), specific capacity (687.65 mAh·gZn-1) and cycling durability (100 h).

Boosting Oxygen Reduction Activity of Co3O4 through a Synergy of Ni Doping and Carbon Species Dotting for Zn-air Battery

Oxygen reduction reaction (ORR) undertakes an indispensable driving role for metal-air batteries with sluggish kinetics. In this work, we proposed a synergic strategy of Ni doping and carbon species dotting to compose Co3O4 with intrinsic large specific area and oxygen vacancies. The Ni-doped Co3O4/C (NCC-1) with four electron transfer mode conducts extraordinary electrocatalytic performance than commercial 20 wt% Pt/C and excellent tolerance to methanol poisoning. This series of improvements are attributed to the rapid dynamics drove by variable transition metal valence with elevated electronic conductivity derived from dotted carbon species. The XPS results at different reduction stages investigate that the doped Co3O4/C affects ORR performance by adjusting the species of *O at the active sites and the formation of intermediates including *OH and *O. More Co3+ active sites exposed on the NCC-1 surface, higher catalytic activity is provided by the conversion of Co(Ⅱ)/Co(III) and Ni(Ⅱ)/Ni(III). What is purposeful in practicability. the NCC-1/IrO2 based Zn-air batteries show an excellent charge-discharge response and cyclability than that of 20% Pt/IrO2 based Zn-air batteries, highlighting the implemented potentiality of NCC-1 based metal-air-battery. This study offers new insights into designing non-noble-metal based oxygen reduction electrocatalysts for more energy storage devices.

Regulation of Atomic Fe-Spin State by Crystal Field and Magnetic Field for Enhanced Oxygen Electrocatalysis in Rechargeable Zinc-Air Batteries.

Highly-active and low-cost bifunctional electrocatalysts for oxygen reduction and evolution are essential in rechargeable metal-air batteries, and single atom catalysts with Fe-N-C are promising candidates. However, the activity still needs to be boosted, and the origination of spin-related oxygen catalytic performance is still uncertain. Herein, an effective strategy to regulate local spin state of Fe-N-C through manipulating crystal field and magnetic field is proposed. The spin state of atomic Fe can be regulated from low spin to intermediate spin and to high spin. The cavitation of dxz and dyz orbitals of high spin Fe(Ⅲ) can optimize the O2 adsorption and promote the rate-determining step (*O2 to *OOH). Benefiting from these merits, the high spin Fe-N-C electrocatalyst displays the highest oxygen electrocatalytic activities. Furthermore, the high spin Fe-N-C-based rechargeable zinc-air battery displays a high power density of 170 mW cm-2 and good stability.

Regulation of Atomic Fe‐Spin State by Crystal Field and Magnetic Field for Enhanced Oxygen Electrocatalysis in Rechargeable Zinc‐Air Batteries

AbstractHighly‐active and low‐cost bifunctional electrocatalysts for oxygen reduction and evolution are essential in rechargeable metal‐air batteries, and single atom catalysts with Fe−N−C are promising candidates. However, the activity still needs to be boosted, and the origination of spin‐related oxygen catalytic performance is still uncertain. Herein, an effective strategy to regulate local spin state of Fe−N−C through manipulating crystal field and magnetic field is proposed. The spin state of atomic Fe can be regulated from low spin to intermediate spin and to high spin. The cavitation of dxz and dyz orbitals of high spin FeIII can optimize the O2 adsorption and promote the rate‐determining step (*O2 to *OOH). Benefiting from these merits, the high spin Fe−N−C electrocatalyst displays the highest oxygen electrocatalytic activities. Furthermore, the high spin Fe−N−C‐based rechargeable zinc‐air battery displays a high power density of 170 mW cm−2 and good stability.

Zinc-Mediated Template Synthesis of Hierarchical Porous N-Doped Carbon Electrocatalysts for Efficient Oxygen Reduction.

The development of highly active and low-cost catalysts for use in oxygen reduction reaction (ORR) is crucial to many advanced and eco-friendly energy techniques. N-doped carbons are promising ORR catalysts. However, their performance is still limited. In this work, a zinc-mediated template synthesis strategy for the development of a highly active ORR catalyst with hierarchical porous structures was presented. The optimal catalyst exhibited high ORR performance in a 0.1 M KOH solution, with a half-wave potential of 0.89 V vs. RHE. Additionally, the catalyst exhibited excellent methanol tolerance and stability. After a 20,000 s continuous operation, no obvious performance decay was observed. When used as the air-electrode catalyst in a zinc-air battery (ZAB), it delivered an outstanding discharging performance, with peak power density and specific capacity as high as 196.3 mW cm-2 and 811.5 mAh gZn-1, respectively. Its high performance and stability endow it with potential in practical and commercial applications as a highly active ORR catalyst. Additionally, it is believed that the presented strategy can be applied to the rational design and fabrication of highly active and stable ORR catalysts for use in eco-friendly and future-oriented energy techniques.

Regulated High‐Spin State and Constrained Charge Behavior of Active Cobalt Sites in Covalent Organic Frameworks for Promoting Electrocatalytic Oxygen Reduction

AbstractA novel type of covalent organic frameworks has been developed by assembling definite cobalt‐nitrogen‐carbon configurations onto carbon nanotubes using linkers that have varying electronic effects. This innovative approach has resulted in an efficient electrocatalyst for oxygen reduction, which is understood by a combination of in situ spectroelectrochemistry and the bond order theorem. The strong interaction between the electron‐donating carbon nanotubes and the electron‐accepting linker mitigates the trend of charge loss at cobalt sites, while inducing the generation of high spin state. This enhances the adsorption strength and electron transfer between the cobalt center and reactants/intermediates, leading to an improved oxygen reduction capability. This work not only presents an effective strategy for developing efficient non‐noble metal electrocatalysts through reticular chemistry, but also provides valuable insights into regulating the electronic configuration and charge behavior of active sites in designing high‐performance electrocatalysts.

Regulated High-Spin State and Constrained Charge Behavior of Active Cobalt Sites in Covalent Organic Frameworks for Promoting Electrocatalytic Oxygen Reduction.

A novel type of covalent organic frameworks has been developed by assembling definite cobalt-nitrogen-carbon configurations onto carbon nanotubes using linkers that have varying electronic effects. This innovative approach has resulted in an efficient electrocatalyst for oxygen reduction, which is understood by a combination of in situ spectroelectrochemistry and the bond order theorem. The strong interaction between the electron-donating carbon nanotubes and the electron-accepting linker mitigates the trend of charge loss at cobalt sites, while inducing the generation of high spin state. This enhances the adsorption strength and electron transfer between the cobalt center and reactants/intermediates, leading to an improved oxygen reduction capability. This work not only presents an effective strategy for developing efficient non-noble metal electrocatalysts through reticular chemistry, but also provides valuable insights into regulating the electronic configuration and charge behavior of active sites in designing high-performance electrocatalysts.

General and scalable strategy for synthesis of Pt-rare earth alloys as highly durable oxygen reduction electrocatalysts

Platinum-rare earth (Pt-RE) alloys are effective oxygen reduction reaction (ORR) catalysts, which are promising to show robust durability in proton-exchange membrane fuel cells (PEMFCs). Whereas, the large difference in reduction potentials between the two kinds of metals and the very oxophilicity of RE elements bring big challenges in the controllable synthesis of Pt-RE alloys. Herein we propose a general and scalable strategy to synthesize Pt-RE catalysts with tunable compositions and microstructures. The as-obtained catalysts possess a lamellar structure with hierarchical pore sizes ranging from 4 to 8 nm and a typical face-centered cubic (FCC) crystalline structure, and the Pt and RE are homogeneously distributed in the alloys. The electronic structures of Pt are well modulated by incorporating RE atoms, resulting in the adjusted d band center for these Pt-RE alloys compare with Pt, which facilitates OH* adsorption behavior and accelerate the ORR kinetics. Furthermore, the energy barrier for Pt demetallation is enhanced by incorporating of RE into the Pt lattice, which significantly enhances ORR durability. Notably, the optimal Pt3Y catalyst exhibits a greatly improved catalytic activity, including a large half-wave potential (0.89 V, at an ultralow Pt loading of 7.8 μg cm−2), high mass activity (0.53 A mg−1 at 0.9 ViR-free) and robust stability (0.01 V decay after 60,000 cycles) exceeding the commercial Pt/C (0.06 V decay after 30,000 cycles). This study provides a new facile strategy for the controllable preparation of Pt-RE alloys, which might pave the way for the large-scale applications of PEMFCs.

Regulating local coordination environment of Mg−Co single atom catalyst for improved direct methanol fuel cell cathode

Fuel cells operated with a reformate fuel such as methanol are promising power systems for portable electronic devices due to their high safety, high energy density and low pollutant emissions. However, several critical issues including methanol crossover effect, CO-tolerance electrode and efficient oxygen reduction electrocatalyst with low or non-platinum usage have to be addressed before the direct methanol fuel cells (DMFCs) become commercially available for industrial application. Here, we report a highly active and selective Mg−Co dual-site oxygen reduction reaction (ORR) single atom catalyst (SAC) with porous N-doped carbon as the substrate. The catalyst exhibits a commercial Pt/C-comparable half-wave potential of 0.806 V (versus the reversible hydrogen electrode) in acid media with good stability. Furthermore, practical DMFCs test achieves a peak power density of over 200 mW cm−2 that far exceeds that of commercial Pt/C counterpart (82 mW cm−2). Particularly, the Mg−Co DMFC system runs over 10 h with negligible current loss under 10 M concentration methanol work condition. Experimental results and theoretical calculations reveal that the N atom coordinated by Mg and Co atom exhibits an unconventional d-band-ditto localized p-band and can promote the dissociation of the key intermediate *OOH into *O and *OH, which accounts for the near unity selective 4e− ORR reaction pathway and enhanced ORR activity. In contrast, the N atom in SACCo remains inert in the absorption and desorption of *OOH and *OH. This local coordination environment regulation strategy around active sites may promote rational design of high-performance and durable fuel cell cathode electrocatalysts.

Simultaneously Incorporating Atomically Dispersed Co‐Nx Sites with Graphitic Carbon Layer‐Wrapped Co9S8 Nanoparticles for Oxygen Reduction in Acidic Electrolyte

AbstractA facile yet robust synthesis is reported herein to simultaneously incorporate atomically dispersed Co‐Nx sites with graphitic layer‐protected Co9S8 nanoparticles (denoted as Co SACs+Co9S8) as an efficient electrocatalyst for oxygen reduction in acidic solution. The Co SACs+Co9S8 catalyst shows low H2O2 selectivity (∼5 %) with high half‐wave potential (E1/2) of ∼0.78 VRHE in 0.5 M H2SO4. The atomic sites of the catalyst were quantified by a nitrite stripping method and the corresponding site density of the catalyst is calculated to be 3.2×1018 sites g−1. Besides, we also found the presence of a reasonable amount of Co9S8 nanoparticles is beneficial for the oxygen electrocatalysis. Finally, the catalyst was assembled into a membrane electrode assembly (MEA) for evaluating its performance under more practical conditions in proton exchange membrane fuel cell (PEMFC) system.

Highly Efficient Oxygen Electrode Obtained by Sequential Deposition of Transition Metal-Platinum Alloys on Graphene Nanoplatelets.

A set of platinum (Pt) and earth-abundant transition metals (M = Ni, Fe, Cu) on graphene nanoplatelets (sqPtM/GNPs) was synthesised via sequential deposition to establish parallels between the synthesis method and the materials' electrochemical properties. sqPtM/GNPs were assessed as bifunctional electrocatalysts for oxygen evolution (OER) and reduction (ORR) reactions for application in unitised regenerative fuel cells and metal-air batteries. sqPtFe/GNPs showed the highest catalytic performance with a low potential difference of ORR half-wave potential and overpotential at 10 mA cm-2 during OER, a crucial parameter for bifunctional electrocatalysts benchmarking. A novel two-stage synthesis strategy led to higher electrocatalytic performance by facilitating the reactants' access to the active sites and reducing the charge-transfer resistance.

Carbon Black‐Supported Single‐Atom CoNC as an Efficient Oxygen Reduction Electrocatalyst for H2O2 Production in Acidic Media and Microbial Fuel Cell in Neutral Media

AbstractSingle metal atom isolated in nitrogen‐doped carbon materials (MNC) are effective electrocatalysts for oxygen reduction reaction (ORR), which produces H2O2 or H2O via 2‐electron or 4‐electron process. However, most of MNC catalysts can only present high selectivity for one product, and the selectivity is usually regulated by complicated structure design. Herein, a carbon black‐supported CoNC catalyst (CB@CoNC) is synthesized. Tunable 2‐electron/4‐electron behavior is realized on CB@Co‐N‐C by utilizing its H2O2 yield dependence on electrolyte pH and catalyst loading. In acidic media with low catalyst loading, CB@CoNC presents excellent mass activity and high selectivity for H2O2 production. In flow cell with gas diffusion electrode, a H2O2 production rate of 5.04 mol h−1 g−1 is achieved by CB@CoNC on electrolyte circulation mode, and a long‐term H2O2 production of 200 h is demonstrated on electrolyte non‐circulation mode. Meanwhile, CB@CoNC exhibits a dominant 4‐electron ORR pathway with high activity and durability in pH neutral media with high catalyst loading. The microbial fuel cell using CB@CoNC as the cathode catalyst shows a peak power density close to that of benchmark Pt/C catalyst.

Edge atomic Fe sites decorated porous graphitic carbon as an efficient bifunctional oxygen catalyst for Zinc-air batteries

The development of advanced bifunctional oxygen electrocatalysts for oxygen reduction and evolution reactions (ORR and OER) is critical to the practical application of zinc-air batteries (ZABs). Herein, a silica-assisted method is reported to integrate numerous accessible edge Fe-Nx sites into porous graphitic carbon (named Fe-N-G) for achieving highly active and robust oxygen electrocatalysis. Silica facilitates the formation of edge Fe-Nx sites and dense graphitic domains in carbon by inhibiting iron aggregation. The purification process creates a well-developed mass transfer channel for Fe-N-G. Consequently, Fe-N-G delivers a half-wave potential of 0.859 V in ORR and an overpotential of 344 mV at 10 mA cm−2 in OER. During long-term operation, the graphitic layers protect edge Fe-Nx sites from demetallation in ORR and synergize with FeOOH species endowing Fe-N-G with enhanced OER activity. Density functional theory calculations reveal that the edge Fe-Nx site is superior to the in-plane Fe-Nx site in terms of OH* dissociation in ORR and OOH* formation in OER. The constructed ZAB based on Fe-N-G cathode shows a higher peak power density of 133 mW cm−2 and more stable cycling performance than Pt/C + RuO2 counterparts. This work provides a novel strategy to obtain high-efficiency bifunctional oxygen electrocatalysts through space mediation.

Template-based synthesis of Co3O4 and Co3O4/SnO2 bifunctional catalysts with enhanced electrocatalytic properties for reversible oxygen evolution and reduction reaction

Porous cobalt (III) oxide (Co3O4) and mixed cobalt (III) oxide - tin oxide (Co3O4/SnO2) were prepared by a novel template-based hydrothermal method resulting in their spherical morphology as confirmed by thorough physico-chemical characterisation. Two oxides were systematically examined as bifunctional electrocatalysts for oxygen reduction (ORR) and evolution (OER) reaction in alkaline media by voltammetry with rotating disk electrode, electrochemical impedance spectroscopy, and chronoamperometry. Low-cost Co3O4 and Co3O4/SnO2 electrocatalysts showed excellent ORR performance with low onset and half-wave potential, low Tafel slope, and the number of exchange electrons near 4, comparable to the commercial Pt/C electrocatalyst. Low OER onset potential of 1.52 and 1.57 V was observed for Co3O4 and Co3O4/SnO2, respectively, with low charge transfer resistance under anodic polarization conditions. Finally, to test bifunctional activity and durability of the two electrocatalyst, switch OER/ORR test was carried out.

Boron doped partially wrapped hierarchical porous carbon materials towards oxygen reduction reaction

Heteroatom-doped metal-free materials have been widely investigated as promising oxygen reduction electrocatalysts because of their cheapness, high activity and environmental friendliness. Herein, a convenient strategy to exploit the volatility of zinc-based MOF (ZIF-8) is cleverly presented in this work, and then ZIF-8 is successfully wrapped with melamine and boric acid as a template to form highly B and N doped metal-free partially wrapped hierarchical porous carbon materials (BN/MPC). The developed BN/MPC catalyst has good catalytic activity for ORR in alkaline electrolytes (Eonset = 0.96 V vs. RHE, E1/2 = 0.78 V vs. RHE) and outstanding long-term stability (retain = 95.7 %). Delightfully, the extraordinary performance is attributed to the structural and compositional features of BN/MPC, including large surface area (937.7 m2 g−1), hierarchical porous structure, B and N co-doping. The electron spin resonance (ESR) can confirm the electron-deficient nature of element B in BN/MPC, proper binding to OH* which in turn facilitates the adsorption of O2 and improves the ORR performance. The as-prepared BN/MPC cathode catalysts exhibits a power density of 105.4 mW cm−2 and a specific capacity of 770 mAh gZn−1 after forming a zinc-air batteries.