Oxygen Reduction Electrocatalysts Research Articles

Effect of Gas-Phase Nitric Oxide Adsorption on ORR Activity of Fe-N-C Catalysts

Significant progress has been made in recent years in developing platinum group metal-free catalysts, particularly so-called Fe-N-C materials, for the oxygen reduction reaction (ORR) in polymer electrolyte fuel cells.1 However, further improvement in both activity and, especially, durability are still necessary for practical applications. One of the major factors that hinder the further enhancement of the catalysts is the lack of clear understanding of the nature of the active sites in the Fe-N-C catalysts due to the complexity of the Fe-N-C catalysts’ composition and structure. Gaseous nitric oxide was reported to be a suitable probe molecule that can bond to Fe and impede the ORR of the Fe-N-C catalysts.2,3 In this work, the effect of nitric oxide gas-phase adsorption on Fe-N-C catalyst redox feature and ORR activity for a variety of Fe-N-C catalysts from different origin will be investigated. The implication of these results on the nature of the ORR active sites of the Fe-N-C catalysts will be discussed.AcknowledgementsThis work was supported by the U.S. Department of Energy (DOE), Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office (HFTO) under the auspices of the Electrocatalysis Consortium (ElectroCat 2.0). This work was partially authored by Argonne, a U.S. Department of Energy (DOE) Office of Science laboratory operated for DOE by UChicago Argonne, LLC under contract no. DE-AC02-06CH11357.References X.X. Wang, M.T. Swihart, and G. Wu, "Achievements, challenges, and perspectives on cathode catalysts in proton exchange membrane fuel cells for transportation", Nature Catalysis, 2 (2019) 578-589.J.L. Kneebone, et al., "A Combined Probe-Molecule, Mossbauer, Nuclear Resonance Vibrational Spectroscopy, and Density Functional Theory Approach for Evaluation of Potential Iron Active Sites in an Oxygen Reduction Reaction Catalyst", J. Phys. Chem. C 121 (2017) 16283-16290.P. Boldrin, D. Malko, A. Mehmood, U.I. Kramm, S. Wagner, S. Paul, N. Weidler, A. Kucernak, “Deactivation, reactivation and super-activation of Fe-N/C oxygen reduction electrocatalysts: Gas sorption, physical and electrochemical investigation using NO and O2”, Applied Catalysis B: Environmental 292 (2021) 120169.

Effects of Bifunctional Oxygen Catalyst Layer Composition on Unitized Regenerative Fuel Cell Performance

Proton exchange membrane unitized regenerative fuel cells (PEM-URFCs) can generate storable fuel (hydrogen) and oxidant (oxygen) which can then be used to produce power from the same cell. Combining electrolysis and fuel cell modes within the same cell allows PEM-URFCs to have the potential for lower mass, volume, and cost compared with discrete fuel cell and electrolyzer systems. The bifunctional oxygen catalyst layer (BOCL) catalyzes the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR) at the same electrode, and there are wide potential differences and opposing mass transport phenomena involved within the BOCL when operating in electrolyzer or fuel cell mode. The BOCL composition, structure and morphology significantly affect performance and stability of PEM-URFCs. In our prior work, we showed bimetallic nanoframes provide bifunctional oxygen electrocatalysts with significantly higher activity compared with monometallic structures, evaluated using a rotating disk electrode configuration.1 We will present our investigation of the effects of the BOCL composition, structure and morphology on URFC membrane electrode assemblies (MEAs) prepared using ultrasonic spraying. Catalyst composition and loading were determined to influence URFC performance, and there are tradeoffs between fuel cell performance, electrolyzer performance, and catalyst cost. In addition to the effects of the active catalyst (either Pt for ORR or IrO2 for OER), our work supports the non-catalytically active component influences MEA performance, which is in agreement with our finding of synergistic effects of Pt and IrO2 within rotating disk electrode measurements.1 We are also evaluating the effects of porous transport layers and different operating conditions on URFC MEA performance and durability over repeated cycling. References Godínez-Salomón, F.; Albiter, L.; Mendoza-Cruz, R.; Rhodes, C.P. Bimetallic Two-dimensional Nanoframes: High Activity Acidic Bifunctional Oxygen Reduction and Evolution Electrocatalysts. ACS Appl. Energy Mater. 2020, 3, 2404-2421.

Computational Search for a Descriptor of Electrocatalysis in Transition Metal-Oxides

Currently, the most effective electrocatalysts for oxygen reduction (ORR) and oxygen evolution reactions (OER) are comprised of noble metal oxides, which bring issues of high cost and scarcity. Discovering earth-abundant alternatives is challenging due to the costly and time-consuming experiments. High-throughput atomistic simulation of catalysts can be an efficient route for enabling the better design and discovery of new electrocatalysts. The efficient use of this approach relies on an activity descriptor that can capture the qualitative and quantitative catalytic trends. In the past, multiple descriptors based on electronic properties have been proposed either reaction-specific or system specific. Therefore, we need a descriptor, which can capture the bonding strength accurately for any sort of reaction or system.In this work, we study the trends of O*/OH* adsorption energies for a wide range of pure metal oxide polymorphs[1] namely rocksalt (MO), corundum (M2O3), rutile (MO2), pentoxide (M2O5) and MO3 in all conceivable oxidation states i.e., +2, +3, +4, +5 and +6 respectively. The main drivers of the adsorption energy are the extent of filling of the bonding and anti-bonding orbitals, along with the spin-dependent coupling strength between the metal-d and oxygen-2p atomic orbitals. This property can be easily captured with the help of crystal orbital Hamiltonian population (COHP). We have observed a strong correlation between the integrated COHP I(COHP) of the bulk system and the adsorption energy, which indicates expensive surface-level electronic calculations can be replaced by bulk-level computations. However, this correlation does not hold on two classes of systems: (i) d0 systems and (ii) systems with significant surface distortion during the reaction. We have considered a different approach to address these systems, where instead of a single bond ICOHP, we account for the summation of the ICOHP around the active site.In search of promising catalysts, we also report tetrahedral systems for 3d, 4d and 5d transition metal oxides, i.e., zinc blende, wurtzite and square planar systems. This will broaden the horizon of possible catalysts along the octahedral systems. We correlate the bulk ICOHP with the surface reactivity of these systems, which highlights the applicability of ICOHP as a universal descriptor across a series of metal oxide systems and guide the design of novel catalysts.This research was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division, Catalysis Science Program to the SUNCAT Center for Interface Science and Catalysis.[1] "Unravelling Electronic Trends in O* and OH* Surface Adsorption in the MO2 Transition-Meta Oxide Series"; Benjamin M. Comer, Jiang Li, Frank Abild-Pedersen, Michal Bajdich, Kirsten Winther, 2022, (ACS J. Phys. Chem C.,)[2] “Predicting O* and OH* Surface Adsorption on Transition Metal Oxides from Bulk Structure”; Benjamin M. Comer, Neha Bothra, Jaclyn Lunger, Frank Abild-Pedersen, Michal Bajdich, Kirsten Winther, Manuscript under preparation.

CoMn2O4 nanoparticles supported on defect-rich N-doped carbon nanotubes as air electrode in rechargeable zinc-air batteries

In this study, an efficient bifunctional electrocatalyst for oxygen reduction and evolution reactions (ORR and OER) was synthetized. The catalyst comprised small-size CoMn2O4 spinel on multi-walled carbon nanotubes (CNT), interface-engineered to introduce defects and nitrogen heteroatoms, and was compared with CoMn2O4 on Vulcan carbon without surface modification. X-ray diffraction analysis confirmed the tetragonal structure with similar crystallite sizes (10–12 nm) on both carbon supports, which was validated by transmission electron microscopy (TEM). The spinel-based catalysts exhibited good activity for oxygen reactions, exhibiting a 4e − pathway for ORR on both supports, with a slightly improved in onset potentials for the supported-on N-CNT, additionally, CoMn2O4/N-CNT demonstrated superior durability, retaining 90–100% of initial current for ORR and OER, while CoMn2O4/C retained 82% and 17%. This effect on stability was corroborated by the Zinc-air battery tests, since, the CoMn2O4/N-CNT was the only catalyst that completed the 260 cycles (around of 72 h), even, the noble catalysts were only able to complete 190 cycles. Additionally, the nanocomposite demonstrated an impressive 910 mA·h/g specific capacity at 5 mA cm−2 discharge rate, surpassing CoMn2O4/C (400 mA·h/g). These findings highlight the potential of the interface-engineered nanomaterial for energy storage, offering a substantial cycling capacity boost.

Hierarchical 2D sheets of N and S co-doped Fe-based electrocatalyst for efficient oxygen reduction in advanced Zn-air battery

Currently, the scientific community is keenly interested in the design and production of efficient and durable transition metal electrocatalysts for oxygen reduction reactions (ORR). Therefore, this study reports a simple and reproducible N and S co-doped two-dimensional (2D) hierarchical porous electrocatalyst is reported. NSC the support material first was obtained by pyrolyzing trithiocyanuric acid (TTCA) and loaded on hemin to obtain the final material named Fe/NSC-800. 2D hierarchical porous structures with the large specific surface area were constructed by using TTCA as the template, S source, and additional N source. The addition of hemin not only retained the morphology of the NSC but also provided source of Fe for Fe/NSC-800. The Fe/NSC-800 possessed the limiting current density of 5.85 mA cm–2 and good ORR stability in 0.1 M KOH solution. Based on the excellent ORR performance of Fe/NSC-800, it was assembled into the primary Zn-air battery, which also exhibited satisfactory open circuit voltage (1.55 V) and energy density (880 W h kg–1). This work has contributed to the rational engineering and fabrication of high-performance ORR electrocatalysts for Zn-air battery applications.

Linkage engineering in covalent organic frameworks as metal-free oxygen reduction electrocatalysts for hydrogen peroxide production

Covalent organic frameworks (COFs) are promising platforms with tailorable structures toward metal-free electrocatalytic oxygen reduction (ORR). Here, COFs with different linkages were constructed and explored in the selective two-electron ORR (2e- ORR) for hydrogen peroxide (H2O2) production. Interestingly, imine-linked Py-TD-COF delivers a remarkable H2O2 selectivity of 80–92 %, while amine-linked Py-TD-COF-NH exhibits relatively low H2O2 selectivity of 50–61 %. Experimental and theoretical results reveal that the donor-accepter property of Py-TD-COF enables proper activation of O2, while Py-TD-COF-NH shows relatively high activation of O2 due to the electronic modulation induced by the linkage transformation. Furthermore, the potential H-bonding between the amine group and the adsorbed oxygen molecules on Py-TD-COF-NH is proved to elongate the OO bond, thus accelerating the subsequent hydrogenation and lowering the barrier for the reduction of *OOH to *O intermediates. This work highlights the importance of suitable linkages and provides a guideline for designing metal-free COF catalysts for 2e- ORR.

Bio‐inspired Design of Bidirectional Oxygen Reduction and Oxygen Evolution Reaction Molecular Electrocatalysts

AbstractThe proper utilization of renewable energy sources has emerged as a major challenge in our pursuit of a sustainable and carbon‐neutral energy landscape. Small molecule activation is a key component for proper utilization of renewable energy resources, where O2/H2O redox couple is reckoned to be a potential game changer. In this regard, electrocatalytic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) have become the prime interest of catalyst designers. Typically, these ORR and OER electrocatalysts are developed distinctly; however, very soon, the requirement of a bidirectional ORR/OER electrocatalyst becomes obvious for practical applicability and rapid energy transduction purposes. A bidirectional catalyst is defined as a catalyst capable of driving a redox reaction in opposing directions. This review has portrayed the development of enzyme structure‐inspired design of molecular bidirectional ORR/OER catalysts. The strategic incorporation of secondary and outer coordination sphere features has significantly enhanced the performance of these catalysts, which can be monitored via the key catalytic parameters. These bifunctional OER/ORR catalysts are vital for metal‐air battery and fuel cell applications and appropriately poised to lay the foundation for an efficient, economical, and eco‐friendly pathway for sustainable energy usage with the rational assembly of energy converting and storage devices.

Fe phthalocyanine stabilized on phosphorous-doped multi-defective carbon nanoribbons as oxygen reduction electrocatalysts

Coordination polymers can be utilized as ideal precursors due to their ability to change their growth behavior and topological structure through solvent-induced effects. In this work, nanostrip-like crystalline particles, transformed from interchangeable indium-based coordination polymers (InOF-25/26), are treated to synthesize phosphorus-doped multi-defective carbon nanoribbons for efficiently anchoring iron phthalocyanine. The obtained FePc-Fe2P@25-CNR electrocatalyst exhibits a superior half-wave potential of 0.899 V and a large diffusion current density of 5.152 mA cm−2 in oxygen reduction reaction (ORR). Meanwhile, it also shows excellent stability in homemade Zn-air batteries with satisfactory charge/discharge durability over 100 cycles. In this case, the ORR performance can be improved by phosphating the carbon surface, reinforcing tight bonding with transition metal phthalocyanines, and inducing charge migration to increase the electrocatalysis kinetics, which is further validated by relevant theoretical calculation. This synthetic strategy combines structurally variable coordination polymers with metallomacrocyclic molecules, exploiting a feasible pathway for the preparation of high-performance electrochemical catalysts.

Directional manipulation of electron transfer in copper/nitrogen doped carbon by Schottky barrier for efficient anodic hydrazine oxidation and cathodic oxygen reduction

Development of bifunctional hydrazine oxidation and oxygen reduction electrocatalysts with high activity and stability is of great significance for the implementation of direct hydrazine fuel cells. Combining zero-dimensional metal nanoparticles with three-dimensional nitrogen-doped carbon nanosheets is an attractive strategy for balancing performance and cost. However, the precise construction of these composites remains a significant challenge, and thorough study of their interaction mechanisms is lacking. Herein, the CuNPs/CuSA-NPCF catalyst was constructed by anchoring copper nanoparticles on a three-dimensional nitrogen-doped porous carbon nanosheet framework through coordination of polyvinyl pyrrolidone and copper ions. The Schottky barrier of metal–semiconductor matched the Fermi level of the rectifying contact, thus enabling directional electron transfer. The resulting electron-deficient Cu nanoparticles surface exhibited Lewis acidity, which was beneficial to adsorption of hydrazine molecule. While the electron-enriched Cu–N4/carbon surface improved the adsorption of oxygen molecule, and accelerated electron supply from Cu-N4 active sites to various oxygen intermediates. The CuNPs/CuSA-NPCF Mott-Schottky catalyst exhibited excellent catalytic activity for hydrazine oxidation reaction and oxygen reduction reaction in an alkaline media. The directional manipulation of electron transfer in heterogeneous materials was an attractive universal synthesis method, providing new approach for the preparation of efficient and stable hydrazine fuel cell catalysts.

Mn-Doped Zn Metal-Organic Framework-Derived Porous N-Doped Carbon Composite as a High-Performance Nonprecious Electrocatalyst for Oxygen Reduction and Aqueous/Flexible Zinc-Air Batteries.

Developing low-cost, efficient, and stable oxygen reduction reaction (ORR) electrocatalysts is crucial for the commercialization of energy conversion devices such as metal-air batteries. In this study, we report a Mn-doped Zn metal-organic framework-derived porous N-doped carbon composite (30-ZnMn-NC) as a high-performance ORR catalyst. 30-ZnMn-NC exhibits excellent electrocatalytic activity, demonstrating a kinetic current density of 9.58 mA cm-2 (0.8 V) and a half-wave potential of 0.83 V, surpassing the benchmark Pt/C and most of the recently reported non-noble metal-based catalysts. Moreover, the assembled zinc-air battery with 30-ZnMn-NC demonstrates high peak power densities of 207 and 66.3 mW cm-2 in liquid and flexible batteries, respectively, highlighting its potential for practical applications. The excellent electrocatalytic activity of 30-ZnMn-NC is attributed to its unique porous structure, the strong electronic interaction between metal Zn/Mn and adjacent N-doped carbon, as well as the bimetallic Mn/Zn-N active sites, which synergistically promote faster reaction kinetics. This work offers a controllable design strategy for efficient electrocatalysts with porous structures and bimetallic active sites, which can significantly enhance the performance of energy conversion devices.

Copper-nitrogen dual-doped activated carbon derived from alder wood as an electrocatalyst for oxygen reduction

In the present study, unmodified nitrogen-doped carbon material (N-doped C) and modified with copper nanoparticles (CuNPs) nitrogen-doped carbon material (Cu-N-doped C) have been synthesized using wood biomass as a carbon precursor, dicyandiamide as a nitrogen precursor, and anhydrous copper acetate as the precursor of Cu. The morphology, structure, and chemical composition of the obtained materials have been analyzed by performing nitrogen sorption experiments and described using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and scanning-electron microscopy (SEM). The electrocatalytic performance of N-doped C and Cu-N-doped C materials has been evaluated for the electro-reduction of oxygen (ORR) in alkaline media using linear scan voltammetry (LSV) and the rotating disk and ring-disk electrode (RDE and RRDE) methods.It has been determined that the nitrogen-doped carbon material and that modified with CuNPs have been synthesized with graphene-like structures and especially high specific surface areas of 2631 m2 g−1 and 2243 m2 g−1, respectively. The onset potential (Eonset) and half-wave (E1/2) potential values are approximately 0.921 V and 0.828 V, respectively, for the N-doped carbon with the loading of 0.0889 mgcat cm−2 and 0.975 V and 0.843 V, respectively, for Cu–N-doped carbon (0.4044 mgcat cm−2), comparable with the commercial Pt/C catalyst.

Structural evolution and performance enhancement of coal-based metal-free N,P-doped porous carbon electrocatalysts for pH-universal oxygen reduction

Structural strengths of carbon-based supports, which hold up catalytically active sites and electron transfer, need to be considered in terms of carbonaceous electrocatalysts because weak supports often give unstable or poor performance in electrochemical environments. Coal can be a reasonable option for an attractive carbon source in view of its low expense, extensive reserve and natural robustness. Conversion of coal to coal-based carbon, instead of conventionally burning it off as fuel to emit CO2, is increasingly finding its own niche in the forefront of chemical engineering. However, pore propagation and surface modification of coal are difficult to handle due to its hardness characteristics, limiting performance enhancement of coal-based catalysts. To tackle this problem, we propose a double-round activation/doping method and disclose significant influences of different reaction sequences on structure-performance correlations. The coal-based metal-free N,P-doped porous carbon materials manifest the improved performance of electrocatalytic oxygen reduction in the alkaline, acidic and neutral electrolytes, along with robust behaviours including good resistance to harmful ions and conceptual demonstration of electrochemical devices. It is also revealed that the electrocatalytic performance of coal-based catalysts is closely related both to their textural properties and to concerted effects induced by the coexistence and uniform distributions of N and P atoms doped into carbon matrices, as demonstrated by the experimental and theoretical results. Consequently, this work gives intriguing insights into structural evolution and performance enhancement of robust coal-based electrocatalysts from the perspective of reaction sequences and provides inspiration for low-carbon utilization of coal in regard to coal-to-carbon transformations.

Mimicking Metalloenzyme Microenvironments in the Transition Metal-Single Atom Catalysts for Electrochemical Hydrogen Peroxide Synthesis in an Acidic Medium.

Electrochemical reduction of oxygen into hydrogen peroxide in an acidic medium offers an energy-efficient and green H2 O2 synthesis as an alternative to the energy-intensive anthraquinone process. Unfortunately, high overpotential, low production rates, and fierce competition from traditional four-electron reduction limit it. In this study, a metalloenzyme-like active structure is mimicked in carbon-based single-atom electrocatalysts for oxygen reduction to H2 O2 . Using a carbonization strategy, the primary electronic structure of the metal center with nitrogen and oxygen coordination is modulated, followed by epoxy oxygen functionalities close to the metal active sites. In an acidic medium, CoNOC active structures proceed with greater than 98% H2 O2 selectivity (2e- /2H+ ) rather than CoNC active sites that are selective to H2 O (4e- /4H+ ). Among all MNOC (M=Fe, Co, Mn, and Ni) single-atom electrocatalysts, the CoNOC is the most selective (> 98%) for H2 O2 production, with a mass activity of 10Ag-1 at 0.60V vs. RHE. X-ray absorption spectroscopy is used to identify the formation of unsymmetrical MNOC active structures. Experimental results are also compared to density functional theory calculations, which revealed that the structure-activity relationship of the epoxy-surrounded CoNOC active structure reaches optimum (ΔG*OOH ) binding energies for high selectivity.

Structural and Reactivity Effects of Secondary Metal Doping into Iron-Nitrogen-Carbon Catalysts for Oxygen Electroreduction.

While improved activity was recently reported for bimetallic iron-metal-nitrogen-carbon (FeMNC) catalysts for the oxygen reduction reaction (ORR) in acid medium, the nature of active sites and interactions between the two metals are poorly understood. Here, FeSnNC and FeCoNC catalysts were structurally and catalytically compared to their parent FeNC and SnNC catalysts. While CO cryo-chemisorption revealed a twice lower site density of M-Nx sites for FeSnNC and FeCoNC relative to FeNC and SnNC, the mass activity of both bimetallic catalysts is 50-100% higher than that of FeNC due to a larger turnover frequency in the bimetallic catalysts. Electron microscopy and X-ray absorption spectroscopy identified the coexistence of Fe-Nx and Sn-Nx or Co-Nx sites, while no evidence was found for binuclear Fe-M-Nx sites. 57Fe Mössbauer spectroscopy revealed that the bimetallic catalysts feature a higher D1/D2 ratio of the spectral signatures assigned to two distinct Fe-Nx sites, relative to the FeNC parent catalyst. Thus, the addition of the secondary metal favored the formation of D1 sites, associated with the higher turnover frequency.

ZIF-derived porous carbon supported cobalt and selenium dual sites enhanced oxygen reduction reaction

Non-noble metal based oxygen-reduction electrocatalysts with high performance in acidic medium are of great importance to application of proton exchange membrane fuel cells (PEMFCs). Dual-sites catalysts with rational design are essential to promote the sluggish kinetics of oxygen reduction reactions (ORR) owing to the synergistic effect. However, the study of dual sites is mainly based on metal atom pairs and need further mechanism exploration for guiding the reasonable design. Herein, a novel designed dual-sites electrocatalyst with high dispersed Co-Nx and Se–C dual sites embedded in ZIF-derived porous carbon frameworks was successfully synthesized, which displayed a positive ORR activity with a half-wave potential of 0.764 V (vs. RHE) as well as a high stability in 0.5 M H2SO4. Besides, the prepared Co–Se–N–C-2 sample exhibited a high ORR activity with a peak power density of 297 mW cm−2 and a low charge-transfer resistant of 0.326 Ω when this catalyst was employed in the H2/O2 fuel cell test. Furthermore, experimental characterizations and theoretical calculations revealed that the constructed Co/Se dual sites had multiple effects. In addition to providing additional active sites, the introduction of Se can effectively modulate the charge redistribution, enhance the efficiency of charge transfer, and reduce the energy barrier of the desorption process of the ORR pathway. These multiple effects promote the ORR kinetics and improve the catalytic performance.

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.