Efficient Bifunctional Oxygen Electrocatalysts Research Articles

FeNi alloy embedded in three-dimensional nitrogen-doped porous carbon as bifunctional oxygen electrocatalysts for rechargeable Zn-air batteries

Iron‑nickel (FeNi) alloy is one of the efficient bifunctional oxygen electrocatalysts for zinc-air batteries (ZABs). However, FeNi alloy nanoparticles prepared by traditional synthesis strategies are easy to agglomerate and have non-uniform sizes, which is not conducive to the improvement of catalytic activity and stability. Here, we have successfully encapsulated two different kinds of nitrogen-rich metal phthalocyanines (MPcs) in situ doping in zeolitic imidazolate framework (ZIF-8) homogeneously by the “double solvents” method. The ligand nitrogen and macrocyclic structure of MPcs encapsulated in ZIF-8 not only helps metal dispersion and enhances the metal-ligand‑nitrogen (M-Nx) structure, but also enhances the graphitisation of three-dimensional (3D) porous carbon after pyrolysis. Thus, a FeNi alloy uniformly embedded in 3D nitrogen-doped porous carbon materials (FeNi@NC) was constructed in the subsequent pyrolysis process and used as an efficient bifunctional oxygen reduction/evolution (ORR/OER) electrocatalyst for rechargeable ZABs. Impressively, the FeNi@NC catalyst carries high half-wave potential (0.850 V) in ORR and the low overpotential (291 mV) in OER, significantly better than Pt/C (0.830 V) and RuO2 (307 mV), respectively. In addition, the rechargeable ZAB assembled with FeNi@NC air cathode has a specific capacity of 649 mW cm−2 and shows no significant degradation after 240 h of charging and discharging cycles. This study provides a new design idea for the manufacture of carbon-supported non-noble metal alloy catalysts with bifunctional oxygen catalytic activity, and verifies the feasibility of regulating the composition of non-noble metals to construct a rechargeable ZABs with excellent performance.

General and facile synthesis of Co/CoO nanoparticals supported by nitrogen-doped graphenic networks as efficient oxygen electrocatalyst forZn-air batteries.

Reasonable design of low-cost, high-efficiency and stable bifunctional oxygen electrocatalysts is of great significance to improve the reaction efficiency of Zn-air batteries, which is still a huge challenge. Here, we report a highly efficient bifunctional oxygen electrocatalyst with three-dimensional (3D) N-doped graphene network-supported cobalt and cobalt oxide nanoparticles (Co/CoO-NG), which can be in situ synthesized by inducing metal ions on metal plates via graphene oxide as an inducer. This 3D network structure and open active center show excellent bifunctional oxygen electrocatalytic activity under alkaline conditions, and can be used as an air electrode in rechargeable Zn-air batteries, with significantly better power density (244.28 mW cm-2) and stability (over 340 h) than commercial Pt/C + RuO2mixtures. This work is conducive to advancing the practical application of graphene-based materials as air electrodes for rechargeable zinc-air batteries.

Glu-Co-Assisted Iron-Based Metal–Organic Framework-Derived FeCo/N Co-Doped Carbon Material as Efficient Bifunctional Oxygen Electrocatalysts for Zn–Air Batteries

A Zn–air battery serves as an energy storage solution to address fossil energy and environmental concerns. However, sluggish kinetics in oxygen reduction reactions (ORRs) and oxygen evolution reactions (OERs) demand innovative, cost-effective, and stable bifunctional catalysts to replace precious metal catalysts. In this study, an FeCo-CNTs/KB catalyst was synthesized by pyrolyzing NH2-MIL-101(Fe) coated with glu-Co and conductive carbon (KB). This hierarchical structure comprises carbon nanotubes (CNTs) grafted onto a carbon matrix, housing abundant FeCo nanoparticles within the nanotubes or matrix. KB introduction enhances FeCo nanoparticle dispersion and fosters uniform CNT formation with smaller diameters, thus exposing active sites. Consequently, the FeCo-CNTs/KB catalyst exhibits remarkable bifunctional electrocatalytic activity: an ORR half-wave potential of 0.84 V and an OER overpotential of 0.45 V (10 mA cm−2). Furthermore, the FeCo-CNTs/KB catalyst in a secondary Zn–air battery showcases enduring charge–discharge performance (≥300 h).

Pd@CoFe Alloys on N-Doped Carbon Derived from Charred Tissue Paper as Synergistic Bifunctional Oxygen Electrocatalysts

Integrating more active components into a catalyst material could facilitate the development of multifunctional electrocatalysts for energy conversion and storage applications. In this study, we developed a multifunctional electrocatalyst, namely, Pd alloyed with Co-Fe deposited on N-doped mesoporous carbon derived from tissue paper (Pd@Co-Fe/N-TDC). The synergism in Pd@Co-Fe/N-TDC, stemming from the interatomic alloy between Pd and Co-Fe, N-doped mesoporous carbon with defective surfaces, distribution of polyhedral Pd nanoparticles, and strong metal-support interfacial interaction, resulted in significantly high electrocatalytic performance for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Pd@Co-Fe/N-TDC was found to be an efficient bifunctional oxygen electrocatalyst, and this was evidenced by a high onset potential (1.01 V) and kinetic current density (2.6 mA/cm2) for the ORR and by a low overpotential (296 mV) and a low Tafel slope value (38 mV/dec) for the OER, along with a small ΔE of 736 mV. The catalyst also exhibited high durability for both ORR and OER, even after 10000 and 5000 cycles, respectively. Theoretical assessment provides an insight into the synergism of active metal sites in Pd@Co-Fe/N-TDC, which showed its potential for use as a non-Pt electrocatalyst for energy applications.

Bifunctional ligand Co metal-organic framework derived heterostructured Co-based nanocomposites as oxygen electrocatalysts toward rechargeable zinc-air batteries

Rational construction of efficient and robust bifunctional oxygen electrocatalysts is key but challenging for the widespread application of rechargeable zinc-air batteries (ZABs). Herein, bifunctional ligand Co metal–organic frameworks were first explored to fabricate a hybrid of heterostructured CoOx/Co nanoparticles anchored on a carbon substrate rich in CoNx sites (CoOx/Co@CoNC) via a one-step pyrolysis method. Such a unique heterostructure provides abundant CoNx and CoOx/Co active sites to drive oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), respectively. Besides, their positive synergies facilitate electron transfer and optimize charge/mass transportation. Consequently, the obtained CoOx/Co@CoNC exhibits a superior ORR activity with a higher half-wave potential of 0.88 V than Pt/C (0.83 V vs. RHE), and a comparable OER performance with an overpotential of 346 mV at 10 mA cm−2 to the commercial RuO2. The assembled ZAB using CoOx/Co@CoNC as a cathode catalyst displays a maximum power density of 168.4 mW cm−2, and excellent charge–discharge cyclability over 250 h at 5 mA cm−2. This work highlights the great potential of heterostructures in oxygen electrocatalysis and provides a new pathway for designing efficient bifunctional oxygen catalysts toward rechargeable ZABs.

Architecting N-doped Carbon Nanotube-Rich Carbon Nanofibers with Biomimetic Vine-Leaf-Whisker Structure as Robust Bifunctional Electrocatalysts for Rechargeable Zn-Air Batteries.

Efficient and durable bifunctional catalysts toward oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are urgently desirable but challenging for rechargeable Zn-air batteries (ZABs), especially flexible wearable ZABs. Inspired by the vine-leaf-whisker structure in nature, we proposed a three-dimensional (3D) hierarchical bifunctional catalyst (denoted as Co-Fe-Zn@N-CNT/CNF) consisting of N-doped carbon nanotubes embedded with abundant CoFe alloy nanoparticles, leaf-shaped N-doped carbon nanoflakes, and porous carbon fibers for rechargeable ZABs. The special biomimetic structure provides a large specific surface area, allowing for high exposure of the active site and ensuring fast mass transport/charge transfer. The close combination of CoFe bimetallic alloys and N-doped carbon nanotubes delivers high electrocatalytic activity, while the coexistence of various active sites such as metal nanoparticles (NPs), metal-Nx, doped N species, and their synergistic interactions endows the catalysts with more active sites. As such, the Co-Fe-Zn@N-CNT/CNF catalyst achieves superior bifunctional catalytic activities for the ORR (a half-wave potential of 0.84 V) and the OER (an overpotential of 326 mV at 10 mA cm-2) in alkaline media, comparable to commercial Pt/C and RuO2. Remarkably, both aqueous and solid-state ZABs assembled with Co-Fe-Zn@N-CNT/CNF catalysts as air electrodes demonstrate excellent charging/discharging performance, high peak power density, and robust long-term cycling stability. More interestingly, the flexible ZAB performs well even under bending conditions, displaying satisfactory device stability and mechanical flexibility. This study presents a new collective morphological-composition-structural engineering strategy for exploiting the efficient bifunctional oxygen electrocatalysts, which is of great significance for high-performance rechargeable ZABs and wearable energy storage devices.

Hierarchically structured Mo1–2C/Co-encased carbon nanotubes with multi-component synergy as bifunctional oxygen electrocatalyst for rechargeable Zn-air battery

The development of efficient and durable non-precious metal-based bifunctional oxygen electrocatalysts is pivotal in realizing cost-effective and high-performance rechargeable Zinc-Air Batteries (ZABs). In this study, a straightforward hydrothermal-melamine-assisted carbonization method is employed to synthesize a hierarchical core-shell structure comprising Mo2C/MoC intertwined with cobalt-incorporated N-doped carbon nanotubes (Mo2C/MoC/Co@CNTs). The synergy between Mo2C/MoC and Co@CNTs is harnessed to achieve remarkable bifunctional OER/ORR activities, as evidenced by a small potential gap (ΔE = Ej = 10 – E1/2) of 0.74 V between OER and ORR. When integrated into a liquid ZAB, the assembled battery delivers a remarkable peak power density of 134 mW cm−2 and exhibits a robust cycling performance, sustaining continuous operation for 275 h at a current density of 10 mA cm−2. This work not only presents a strategic approach to developing electrocatalysts with specific components, but also underscores the significance of multi-component synergy in electrocatalytic applications.

Self‐Assembled 3D N/P/S‐Tridoped Carbon Nanoflower with Highly Branched Carbon Nanotubes as Efficient Bifunctional Oxygen Electrocatalyst Toward High‐Performance Rechargeable Zn‐Air Batteries

AbstractHeteroatom doping and 3D nanostructures with large specific surface area and hierarchical porous structure can synergically improve oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). In this study, the 3D N/P/S‐tridoped nanoflower with highly branched carbon nanotubes bifunctional catalyst (Co/SP‐NC) is prepared by a simple self‐assembly pyrolysis method. The powerful driving force of coordination interaction of ammonium ion can promote the self‐assembly of 2D ZnCo‐ZIF nanosheets into 3D ZnCo/S‐ZIF nanoflowers at room temperature stirring. The 3D ZnCo/S‐ZIF nanoflower surface is driven by sodium hypophosphite to form highly branched carbon nanotubes during the pyrolysis process. Moreover, Density functional theory (DFT) calculations also confirm that the simultaneous introduction of N/P/S can promote the redistribution of electron density at the catalyst interface. The proper P‐doping not only enhances the electronic conductivity of the substrate, but also facilitates the charge transfer in the OER/ORR process. Therefore, Co/SP‐NC cathode assembled zinc‐air batteries (ZABs) have a higher power density (187 mW cm−2), a larger specific capacity (801 mAh gZn−1) and excellent cycle stability compared to Pt/C‐RuO2 assembled ZABs. This work will pave the way to regulate the components interactions by designing 3D hierarchical porous structures.

Metal-Oxygen Covalency Competition of Unsymmetrical Metal Pairs for Enhanced Bifunctional Oxygen Electrocatalysis

Rechargeable zinc-air batteries are considered promising energy conversion devices due to their inherent safety and high energy-to-cost ratio. However, the sluggish kinetics of oxygen evolution reaction and oxygen reduction reaction during the charging-discharging process lead to low round trip efficiency and power density. The synthesis of efficient and stable bifunctional oxygen electrocatalysts constitutes the bottleneck to construct applicable ZABs.Here, we report an Mn-doped ruthenium oxide electrocatalyst that exhibits remarkable ORR/OER activity, with a low potential gap of 0.62V between the half-wave potential of ORR and the OER potential at 10mA cm-2. The Mn-RuO2 assembled ZABs present a high power density of 179 mW cm-2 and long lifespans of 800 h. Metal covalency competition induces surface Mn atoms shows more favorable adsorption behavior for ORR and Ru atoms shows more favorable adsorption behavior for OER. The charge redistribution between asymmetrical Ru-O-Mn pairs results in dual actives sites towards OER/ORR. The surface ruthenium stabilizes the O* intermediate due to the weaker hybridization of the lattice Ru-O bond. The upshift of the dz2 orbital relieves the over-binding of the critical intermediates OH* on the Mn atom. Such dual Ru-Mn sites minimized the OER/ORR activity gap restricted by scaling relationships. Our findings rationalize the double active sites mechanism in Mn-RuO2 electrocatalyst and provide a strategy to enhance bifunctional catalytic performance. Figure 1

Designing Bifunctional Oxygen Electrocatalysts Using Prussian Blue Analogue and Carbon Nanostructure Hybrids: Understanding the Role of Individual Components for Oxygen Reduction and Evolution Reactions

The incorporation and identification of active sites for OER and ORR is required for designing an efficient bifunctional oxygen electrocatalyst for low cost and high activity of electrochemical devices such as metal air batteries and regenerative fuel cells. In this work, we synthesized CoHCF/GO/f-CNT nanocomposite which showed excellent bi-functional activity with a low overvoltage of 0.8 V between the oxygen evolution reaction (E10 mA/cm 2) and the oxygen reduction reaction (E1/2). The specific functions of CoHCF and GO/f-CNT were described using hydrodynamic voltammetry measurements. For comparison, the pristine CoHCF and the composites with multiwalled carbon nanotubes (CoHCF/f-CNT) and graphene oxide (CoHCF/GO) were also synthesized and thoroughly characterised for physico-chemical and electrochemical properties. It was observed that CoHCF itself had poor ORR activity which increased on addition of GO/f-CNT. Electrochemical analysis suggested that CoHCF is primarily responsible for the OER activity in nanocomposites. The carbon nanostructure, due to strong metal support interactions (SMSI) and electrical conductivity helped in maximising the utilization of PBA active sites on the surface along with acting like a co-catalyst for ORR. The nanoscale geometries of the PBA and GO/CNT further enhanced the metal support and charge transfer interactions, thereby enhancing the activity. The findings of this study provide an insight for developing more effective PBA based nanocomposites for bifunctional OER/ORR electrocatalysis.

Efficient Bifunctional Oxygen Electrocatalysts for Rechargeable Zn−air Batteries Derived from Ni‐modified Prussian Blue

AbstractThe rational design and exploration of efficient, low‐cost and durable bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are key to the development of rechargeable metal−air batteries. Here, we report a novel approach to in‐situ synthesize Fe0.64Ni0.36 nanoalloy encapsulated in nitrogen‐doped porous carbon nanotubes (FeNi@N−CNTs) as bifunctional electrocatalyst derived from Ni‐modified Prussian blue, on which the ORR/OER can be promoted by the N−CNTs surface due to the electron modulation caused by electron transfer from the inner FeNi nanoalloy to the N−CNTs surface. The abundant wide‐size range of mesopores in N−CNTs can offer rapid mass transport channels to facilitate the catalytic reactions. In addition, the encapsulation structure endows the outer N−CNTs acting as a “shield” to prevent the inner FeNi nanoalloy from corrosion in strong basic medium. Thanks to the synergistic effect between the N−CNTs and FeNi nanoalloy, the obtained FeNi@N−CNTs exhibits excellent bifunctional oxygen catalytic activity together with outstanding performance and cycling durability in rechargeable Zn−air battery. This work will open new avenues for the development of advanced bifunctional electrocatalysts for other metal−air batteries.

Directly assembling initial metal–organic framework and covalent organic polymer toward bifunctional oxygen electrocatalysts for Zn-air flow battery

Developing highly efficient bifunctional oxygen electrocatalysts is important but still remains a challenge for Zn-air flow battery. Metal-organic frameworks (MOFs) and covalent organic polymers (COPs) materials have emerged as promising alternatives to the benchmark precious metal electrocatalysts due to their designable and controllable structures at the atomic level. However, their catalytic performances are limited by the conductivity and catalytic activity using initial materials. Moreover, these materials are generally developed either as single oxygen reduction reaction (ORR) or oxygen evolution reaction (OER) electrocatalysts. Herein, we utilize the π-π stacking effect to directly assemble initial nanosheet FeNi-MOF and iron phthalocyanine rich COP hybrid materials toward the highly efficient bifunctional electrocatalysts via pyrolysis-free strategy. The carbon black is added to the composite as support to limit the stacking of composites and increase the conductivity. The obtained catalyst, named as NSFeNi@COPFe-C, exhibits superior catalytic performance with an ORR onset potential of 0.99 V (vs. reversible hydrogen electrode: RHE), half-wave potential of 0.9 V (vs. RHE), and the OER potential of 1.65 V at 10 mA cm−2 in alkaline electrolyte. The assembled zinc-air flow battery with NSFeNi@COPFe-C as the bifunctional oxygen electrocatalyst shows a discharge power up to 115 mW cm−2 and a long-term stability.

Densely populated trimetallic single-atoms for durable low-temperature flexible zinc-air batteries

The fundamental challenge of trimetallic single-atoms catalysts stems from the difficulty in supporting the coexistence of different metals with their unique physicochemical features. Here, the trimetallic single-atoms electrocatalyst is constructed as a model system to explore electrocatalytic ORR/OER. The tri-metal (Fe, Co, and Ni) single-atoms loaded on nitrogen-carbon framework exhibits superior ORR/OER kinetics (E1/2 = 0.927 V, Ej=10 = 1.56 V). The flexible zinc-air batteries generate excellent power density and durability (62 mW cm−2 and 200 h at −15 °C, 291.2 mW cm−2 and 250 h at room temperature). Density functional calculations confirm that the trimetallic synergy effect outperform mono- and bimetallic effects, yielding adsorption strength close to 0. This paper describes an intuitionistic descriptor where ΔEOH* displays a volcano relationship with ORR overpotential, and establishes a generalized strategy for efficient bifunctional oxygen electrocatalyst while comprehensively understanding the structure-mechanism-activity relationship.

Nickel Phosphonate MOF Derived N-Doped Carbon-Coated Phosphorus-Vacancies-Rich Ni2 P Particles as Efficient Bifunctional Oxygen Electrocatalyst.

The design of non-noble metal bifunctional electrocatalysts with outstanding performance and remarkable stability for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is one of the most essential issues to the realization of rechargeable zinc-air battery, and transition metal phosphides (TMPs) have emerged as robust candidates for oxygen electrocatalysts. Herein, N-doped carbon-coated phosphorus-vacancies-rich Ni2 P particles (Vp -Ni2 P@NC) is proposed via simple carbonization and following Ar plasma treatment from a single nickel phosphonate metal-organic framework (MOF) without extra phosphine and nitrogen sources. The facile and rapid plasma treatment can achieve phosphorus vacancies which could modulate the electronic structure to enhance the inherent active and electrical conductivity. Meanwhile, the pyridine-N and graphitized-N produced during calcination also could provide more active sites and increase the electrical conductivity. The resultant Vp -Ni2 P@NC catalyst shows excellent bifunctional electrocatalytic activity (OER/ORR) based on synergistic effect of introducing P vacancies into Ni2 P and N-doped carbon. Vp -Ni2 P@NC catalyst shows more advantageous ΔE value (0.70 V) compared to Pt/C+RuO2 (0.73 V) and most reported catalysts. Additionally, the zinc-air bbatterie (ZAB) employing Vp -Ni2 P@NC as air cathode shows excellent performance. The maximum power density of 203.48 mW cm-2 , the cycling stability of more than 150 h at 10 mA cm-2 .

Compositional Tuning of Nickel Sulfoselenides for Use As Bifunctional Oxygen Electrocatalysts in Aqueous Electrochemical Energy Storage

Increasing grid-scale deployment of intermittent energy sources necessitates the development of advanced energy storage technologies. Electrochemical energy storage technologies using alkaline electrolytes, especially secondary Zn-air batteries, are uniquely suitable, using inexpensive, non-flammable aqueous electrolytes and making extensive use of earth abundant elements (C, Zn, Mn, etc.). Unfortunately, development of Zn-air batteries is currently limited by electrochemical challenges at both the Zn anode and the air cathode, with the limitations at the air cathode being particularly complex. An ideal cathode would use a bifunctional oxygen electrocatalyst (BOE) capable of efficiently and sequentially catalyzing both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). Precious metal-containing materials (Pt, RuO2, etc.) are currently the most efficient BOEs, but their high cost makes them unideal for commercialization. Transition metal chalcogenides (e.g., NiS2, Ni3Se2) have previously been used as BOEs, but are still relatively underdeveloped alternatives to precious metal electrocatalysts.In this presentation, we report the electrocatalytic performance of a series of compositionally-tunable nickel sulfoselenides (Ni3(S,Se)2, NiSSe) for use as BOEs in Zn-air batteries in place of existing precious metal electrocatalysts. These materials have previously shown promise as OER electrocatalysts, but their ORR and BOE performance has not yet been explored. We demonstrate the synthesis of a range of NiSSe materials with variable S/Se composition, and subsequently use multiple characterization techniques, including cyclic voltammetry, X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS), and others, to explore the performance of these materials as BOE electrocatalysts. The nanoscale NiSSe materials show homogeneous mixing of S/Se over a wide compositional range (10-90% Se), and electrocatalytic testing shows that this S/Se composition has an observable impact on the OER/ORR performance. Roughly 50/50 mixtures showed the best OER performance, while pure Ni3Se2 showed the best ORR performance. As a result, optimum BOE performance of the mixed NiSSe materials was observed near a composition of Ni3S0.4Se1.6; the (electro)chemical stability of this mixed NiSSe was subsequently evaluated using chronoamperometry and XPS. Compared with the binary Ni3S2 and Ni3Se2 compounds, NiSSe was found to be reasonably stable after testing and is therefore a promising candidate for use in air cathodes. As a demonstration, we then tested this NiSSe electrocatalyst in a Zn-air battery and found good agreement with the results from previous the Zn-free experiments. Together, our results show that nickel sulfoselenides are a promising class of tunable electrocatalysts with applications in oxygen electrocatalysis for energy storage.This work was supported by the U.S. Department of Energy, Office of Electricity, and the Laboratory Directed Research and Development program at Sandia National Laboratories, a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA-0003525. This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science. Dr. Imre Gyuk, Director of Energy Storage Research, Office of Electricity is thanked for his financial support. The views expressed herein do not necessarily represent the views of the U.S. Department of Energy or the United States Government.

Hollow Co/N-C@NiCo2O4 Spheres as Highly Efficient Bifunctional Oxygen Electrocatalysts for Rechargeable Zinc–Air Batteries

Hollow Co/N-C@NiCo₂O₄ Spheres as Highly Efficient Bifunctional Oxygen Electrocatalysts for Rechargeable Zinc–Air Batteries

The Heterointerface between Fe1/NC and Selenides Boosts Reversible Oxygen Electrocatalysis

AbstractThe rational design and construction of efficient and inexpensive bifunctional oxygen electrocatalysts are highly desirable for the development of rechargeable Zn–air batteries (ZABs). Although single‐atom Fe sites anchored on N‐doped carbon catalysts (Fe1/NC) ensure high oxygen reduction reaction activity, their unitary atomically dispersed active center faces difficult condition in catalyzing oxygen evolution reaction simultaneously. Herein, a composite catalyst containing heterointerface between Fe1/NC and selenides ((Fe,Co)Se2) is constructed. The obtained (Fe,Co)Se2@Fe1/NC exhibits extremely narrow potential gap of 0.616 V and remarkable stability in alkaline media, outperforming the benchmark catalysts (Pt/C+RuO2: 0.720 V). Experimental results and density functional theory calculations reveal that heterointerface between Fe1/NC and (Fe,Co)Se2 accelerates the electron transfer and provides more moderate adsorption sites, which endow (Fe,Co)Se2@Fe1/NC with extremely high bifunctional oxygen catalytic activity. This study not only provides a superior bifunctional catalyst for ZABs, but also enriches the application of single‐atom catalysts in multifunctional energy storage and conversion devices.

Glucose‐hexamethylenetetramine‐derived Co, N Co‐doped Carbon Nanoflowers with Encapsulated Co@Co3O4 as Efficient Bifunctional Oxygen Electrocatalyst for Zinc‐air Batteries

AbstractDeveloping low‐cost, eco‐friendly, and efficient bifunctional electrocatalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is an important issue for zinc‐air batteries. In this study, HMT‐Co/G‐700 catalyst with nanoflower structure and Co, N co‐doped carbon encapsulated Co@Co3O4 nanoparticles are synthesized from D‐glucose, hexamethylenetetramine (HMT), and Co(NO3)2. HMT is presented as the complex to uniformly disperse Co@Co3O4 nanoparticles, dope nitrogen, and create the nanoflower structure. The nanoflower structure enhances high surface area to expose the active sites. The formation of Co3O4 via mild oxidation of Co surface provides oxygen vacancies to adsorb O2. HMT‐Co/G‐700 catalyst exhibits excellent ORR electrocatalytic property, i. e. high onset potential (1.03 V), high half‐wave potential (0.83 V), low Tafel slope (85.9 mV dec−1), and superior OER activity. Especially, the HMT‐Co/G‐700 catalyst assembled rechargeable zinc‐air battery present high‐power density (111.0 mW cm−2) and long cycle life at 10 mA cm−2 (576 cycles).

Strong interaction and confine effect of manganese oxide-cobalt embedded in self-templated nitrogen-doped carbon enable ultra-stable zinc-air batteries

Developing efficient bifunctional oxygen electrocatalysts with high stability is of great significance for the implementation of rechargeable Zn–air batteries. Herein, MOC-NC bifunctional electrocatalyst with active MnO–Co components embedded in the N-doped carbon sphere is prepared by facile hydrothermal conversion and post-pyrolysis process. The strong interaction between MnO and Co, and confine effect induced by the microstructure endow the fabricated MOC-NC composite with modified electronic configuration, improved conductivity, and significantly reinforced stability. Consequently, the MOC-NC electrocatalyst exhibits good activity and ultrahigh stability for oxygen electrocatalysis. Moreover, when the catalyst was applied to the cathode electrode for the zinc-air battery, it shows excellent performance (specific capacity of 718 ​Wh kgZn−1, power density of 152.3 ​mW ​cm−2) and extraordinary long-term stability (after 200 ​h of charge and discharge cycling, the round-trip efficiency still maintains at 44%). The present work demonstrates a strategy for synthesizing ultrastable bifunctional non-precious metal electrocatalysts for oxygen electrocatalysis.

Nitrogen-Rich Porous Carbon Nanotubes Coated Co/Mo2N Composites Derived from Metal-Organic Framework as Efficient Bifunctional Oxygen Electrocatalysts

Noble metal catalysts such as Pt/C and RuO2 are the most efficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts and show excellent activity. However, their high costs, scarcity, single function, and weak durability impede their large-scale practical application. Therefore, it is paramount to design bifunctional electrocatalysts with high activity, long durability, and low cost. In this work, we used the functionalized modification and hierarchical porous structure of MOFs and adjusted the ratio of Co/Mo atoms to prepare uniformly dispersed nanospheres. The uniform porous nitrogen-doped carbon nanotubes coated with Co/Mo2N composites were obtained by trapping the volatile CNx during high-temperature pyrolysis via a vapor deposition strategy. The physical and chemical properties of the materials were analyzed by various characterization methods such as XRD, XPS, TEM, SEM, Raman, and BET. Notably, CoMoN@NCNTs-700 exhibited excellent ORR/OER bifunctional electrocatalytic activity in alkaline conditions due to the synergistic effect of porous nitrogen-doped carbon nanotubes and the unique heterostructure of Co/Mo2N. In 0.1 M KOH, its ORR half-wave potential was E1/2 = 0.78 V, with a limiting current density even reached to 5.3 mA cm−2 and its operating potential was 1.60 V at a current density of 10 mA cm−2. At the same time, CoMoN@NCNTs-700 also showed better stability and methanol resistance than the commercial catalysts. This work provides a valuable reference for the design and construction of inexpensive non-noble metal bifunctional electrocatalysts.