Commercial RuO2 Research Articles

Fluorine-decoration induced deep reconstruction of iron cobalt oxide for high-efficiency oxygen evolution reaction

The oxygen evolution reaction (OER) is a pivotal process in water electrolysis systems, yet developing cost-effective and highly active OER electrocatalysts from earth-abundant materials through straightforward methods remains a formidable challenge. In this study, FeCo oxides and their fluorides are synthesized using a one-step room-temperature process followed by fluorination with fluorine gas. We compared the OER performance of Fe, Co, and FeCo oxides and investigated the impact of fluorine doping on their physical properties and OER efficiency. Results revealed that the FeCo–O bimetallic oxide exhibited an overpotential of 370 mV in an alkaline electrolyte at a current density of 10 mA/cm2, significantly surpassing the performance of monometallic Fe–O (1 V) and Co–O (467 mV). Fluorine modification markedly enhanced the OER activity of these materials, with Fe-OF at 570 mV, Co-OF at 330 mV, and FeCo-OF at 285 mV. Notably, FeCo-OF demonstrated a stable overpotential lower than commercial RuO2 (289 mV) during a continuous 12 h OER test. Electrochemical analyses and spectral characterizations indicated that fluorine ion electronic regulation facilitated efficient electrocatalytic active sites in the spent FeCo-OF catalyst through in situ self-reconstruction, leading to its stable and superior OER performance. Density functional theory (DFT) calculations confirmed that fluorine modification of the bimetallic oxides decreased the O* Gibbs free energy from 4.86 to 2.44 eV, thereby enhancing the kinetics of the OER reaction.

Metal–organic framework–derived trimetallic particles encapsulated by ultrathin nitrogen-doped carbon nanosheets on a network of nitrogen-doped carbon nanotubes as bifunctional catalysts for rechargeable zinc–air batteries

Economical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) bifunctional catalysts with high activity aimed at replacing precious metal catalysts for rechargeable zinc-air batteries (ZABs) must be developed. In this study, a multiple hierarchical-structural material is developed using a facile dielectric barrier discharge (DBD) plasma surface treatment, solvothermal reaction, and high-temperature carbonization strategy. This strategy allows for the construction of nanosheets using nitrogen-doped carbon (NC) material-encapsulated ternary CoNiFe alloy nanoparticles (NPs) on a network of NC nanotubes (NCNTs), denoted as CoNiFe–NC@p–NCNTs. Precisely, the presence of abundant CoNiFe alloy NPs and the formation of M–N–C active sites created by transition metals (cobalt, nickel, and iron) coupled with NC can provide superior OER/ORR bifunctional properties. Moreover, the prepared NC layers with a multilevel pore structure contribute to a larger specific surface area, exposing numerous active sites and enhancing the uniformity of electron and mass movement. The CoNiFe0.08–NC@p–NCNTs show remarkable dual functionality for electrochemical oxygen reactions (ORR half-wave potential of 0.811 V, limiting current density of 5.73 mA cm−2 measured with a rotating disk electrode at a rotation speed of 1600 rpm, and OER overpotential of 351 mV at 10 mA cm−2), which demonstrates similar ORR performance to 20 wt% Pt/C and better OER performance than the commercial RuO2. A liquid ZAB prepared using the proposed material has excellent bifunctionality with an open-circuit voltage of 1.450 V and long-term cycling stability of 230 h@10 mA cm−2.

Directed Surface Reconstruction of Fe Modified Co2VO4 Spinel Oxides for Water Oxidation Catalysts Experiencing Self-Terminating Surface Deterioration.

Affordable highly efficient catalysts for electrochemical oxygen evolution reaction (OER) play pivotal roles in green hydrogen production via water electrolysis. Regarding the non-noble metal-based electrocatalysts, considerable efforts are made to decipher the cation leaching and surface reconstruction; yet, little attention is focused on correlating them with catalytical activity and stability. Herein, in situ reconstruction of Fe-modified Co2VO4 precursor catalyst to form a highly active (Fe,V)-doped CoOOH phase for OER is reported, during which partial leaching of V accelerates the surface reconstruction and the V reserved in the reconstructed CoOOH layer in the form of alkali-resistant V2O3 serves for dynamic charge compensation and prevention of excessive loss of lattice oxygen and Co dissolution. Fe substitution facilitates Co pre-oxidation and endows the catalysts with structural flexibility by elevating O 2p band level; hence, encouraging participation of lattice oxygen in OER. The optimized Co2Fe0.25V0.75O4 electrode can afford current densities of 10 and 500 mA cm-2 at low overpotentials of 205 and 320 mV, respectively, with satisfactory stability over 600 h. By coupling with Pt/C cathode, the assembled alkaline electrolyzer can deliver 500 mA cm-2 at a low cell voltage of 1.798 V, better than that of commercial RuO2 (+) || Pt/C (-).

Self-Supported WO3@RuO2 Nanowires for Electrocatalytic Acidic Water Oxidation.

Developing catalysts with high catalytic activity and stability in acidic media is crucial for advancing hydrogen production in proton exchange membrane water electrolyzers (PEMWEs). To this end, a self-supported WO3@RuO2 nanowire structure was grown in situ on a titanium mesh using hydrothermal and ion-exchange methods. Despite a Ru loading of only 0.098 wt %, it achieves an overpotential of 246 mV for the oxygen evolution reaction (OER) at a current density of 10 mA·cm-2 in acidic 0.5 M H2SO4 while maintaining excellent stability over 50 h, much better than that of the commercial RuO2. After the establishment of the WO3@RuO2 heterostructure, a reduced overpotential of the rate-determining step from M-O* to M-OOH* is confirmed by the DFT calculation. Meanwhile, its enhanced OER kinetics are also greatly improved by this self-supported system in the absence of the organic binder, leading to a reduced interface resistance between active sites and electrolytes. This work presents a promising approach to minimize the use of noble metals for large-scale PEMWE applications.

Synergy of Ni Nanoclusters and Single Atom Site: Size Effect on the Performance of Electrochemical CO2 Reduction Reaction and Rechargeable Zn−CO2 Batteries

AbstractThe design of bifunctional electrocatalysts toward reduction reaction of carbon dioxide (ECO2RR) and oxygen evolution reaction (OER) in aqueous rechargeable Zn─CO2 batteries (ZABs) still poses a significant challenge. Herein, Ni clusters (Nix) of 0.5 and 0.8 nm in diameter coupled with single Ni site (Ni−N4−C), denoted as Ni−N4/Ni5 and Ni−N4/Ni8, respectively, are synthesized and the size effect of Ni nanoclusters are studied. Ni−N4/Ni5 exhibits an ≈100% Faradaic efficiency (FECO) toward ECO2RR for CO from −0.4 to −0.8 V versus the reversible hydrogen electrode, superior to that of Ni−N4−C (FECO = 55.0%) and Ni−N4/Ni8 (FECO = 80.0%). The OER performance of Ni−N4/Ni5 and Ni−N4/Ni8 are superior or comparable to that of commercial RuO2 but outperform that of Ni−N4−C. Theoretical calculation indicates that *COOH of ECO2RR intermediates bond synergistically with Nix clusters and Ni−N4−C single atom site, promoting the activation of CO2 and reducing the energy barrier of the potential determining step of ECO2RR. Such effect is strongly size‐dependent and larger Nix nanoclusters result in too strong binding of *COOH intermediates, impede the formation of *CO. As a bifunctional cathode electrocatalyst of rechargeable alkaline aqueous ZABs, Ni−N4/Ni5 exhibits a peak power density of 11.7 mW cm−2 and cycling durability over 1200 cycles and 420 h.

Hydrothermally synthesized rGO based FeSe nanocomposite as electrocatalyst for oxygen evolution reaction

Highly productive catalysts are necessary in oxygen evolution reaction (OER) to lower overpotential and enhance sluggish kinetics of the reaction. In this work, we present an effective OER electrocatalyst, i.e. composite of FeSe with reduced graphene oxide (FeSe/rGO) fabricated via hydrothermal method. Its main challenges include low electron conductivity and inadequate active site exposure. Meanwhile, the reduced graphene oxide (rGO) composite improves the conductivity, which raises OER activity and provides large electrochemical surface area. Different physical techniques were used to analyze the composite, according to BET surface area of FeSe/rGO was (201 cm3 g−1). To assess electrochemical characteristics of composite electrochemical impedance spectroscopy (EIS) cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometry was utilized. In comparison to benchmark of commercial RuO2, the FeSe/rGO catalyst exhibits a reduced overpotential (194 mV) and minimal Tafel slope (31 mV dec−1). FeSe/rGO exhibits exceptional stability and long-term durability to be used for OER. This work not only show low overpotential value of FeSe/rGO nanocomposite, but it also introduces a novel method for producing composite materials that are inexpensive and perform well and can be utilized in different future applications.

Surface-Diffusion-Induced Amorphization of Pt Nanoparticles over Ru Oxide Boost Acidic Oxygen Evolution.

Phase transformation offers an alternative strategy for the synthesis of nanomaterials with unconventional phases, allowing us to further explore their unique properties and promising applications. Herein, we first observed the amorphization of Pt nanoparticles on the RuO2 surface by in situ scanning transmission electron microscopy. Density functional theory calculations demonstrate the low energy barrier and thermodynamic driving force for Pt atoms transferring from the Pt cluster to the RuO2 surface to form amorphous Pt. Remarkably, the as-synthesized amorphous Pt/RuO2 exhibits 14.2 times enhanced mass activity compared to commercial RuO2 catalysts for the oxygen evolution reaction (OER). Water electrolyzer with amorphous Pt/RuO2 achieves 1.0 A cm-2 at 1.70 V and remains stable at 200 mA cm-2 for over 80 h. The amorphous Pt layer not only optimized the *O binding but also enhanced the antioxidation ability of amorphous Pt/RuO2, thereby boosting the activity and stability for the OER.

γ-MnO2 as an Electron Reservoir for RuO2 Oxygen Evolution Catalyst in Acidic Media.

Developing highly active and durable catalysts in acid conditions remains an urgent issue due to the sluggish kinetics of oxygen evolution reaction (OER). Although RuO2 has been a state-of-the-art commercial catalyst for OER, it encounters poor stability and high cost. In this study, the electronic reservoir regulation strategy is proposed to promote the performance of acidic water oxidation via constructing a RuO2/MnO2 heterostructure supported on carbon cloth (CC) (abbreviated as RuO2/MnO2/CC). Theoretical and experimental results reveal that MnO2 acts as an electron reservoir for RuO2. It facilitates electron transfer from RuO2, enhancing its activity prior to OER, and donates electrons to RuO2, improving its stability after OER. Consequently, RuO2/MnO2/CC exhibits better performance compared to commercial RuO2, with an ultrasmall overpotential of 189mV at 10mA cm-2 and no signs of deactivation even after 800h of electrolysis in 0.5m H2SO4 at 10mA cm-2. When applied as the anode in a proton exchange membrane water electrolyzer, the cost-efficient RuO2/MnO2/CC catalyst only requires a cell voltage of 1.661V to achieve the water-splitting current of 1 A cm-2, and the noble metal cost is as low as US$ 0.00962 cm-2, indicating potential for practical applications.

CoP nanoparticles embedded in N-doped carbon for highly efficient oxygen evolution reaction electrocatalysis

Development of high-activity and low-cost electrocatalysts is significant to enhance the low-kinetic process of oxygen evolution reaction (OER). In this paper, we utilized the self-assembly between melamine, phytic acid and cobalt ions to obtain two-dimensional Co-MPA. Subsequently, in situ phosphating of cobalt ions to obtain CoP/N-CNT was achieved by the pyrolytic of Co-MPA. The small size of CoP (∼18 nm) and the N-doped carbon material endowed CoP/N-CNT with excellent OER electrocatalytic activity, which delivered an overpotential of 330 mV to drive a current density of 10 mA cm−2. Moreover, the TOF value of CoP/N-CNT catalyst is 4.6 times higher than the commercial RuO2 catalyst (at the overpotential of 480 mV), providing it as a promising electrocatalyst for OER.

Composition-tunable Co3-xFexSe4 as efficient electrocatalysts for the oxygen evolution reaction

In the oxygen evolution reaction (OER), the selection of highly active catalysts is fundamental to curtail overpotentials and to enhance the typically sluggish kinetics characteristic of the reaction. Cobalt selenide (Co3Se4), with its optimally configured electronic structure of cobalt ions, is consistently hailed as a prospective electrocatalyst for the OER, making it highly efficient in facilitating the reaction.Despite the persistent challenges of the exposure of catalytic active sites and the limited electronic conductivity, our study unveils a breakthrough solution. We introduce a highly efficient Fe-doped Co3Se4 electrocatalyst for the OER, addressing these long-standing issues, and it has desirable compositional flexibility, formed Co3-xFexSe4 (0 ≤ x ≤ 3) selenides, by introducing Fe doping, the electronic structure of Co3Se4 is effectively regulated, resulting in a remarkable reduction in the overpotential of the OER under alkaline conditions.Simultaneously, the introduction of Fe induces the formation of highly active Co–O sites, ultimately establishing a highly active and stable catalytic surface for oxygen evolution. Consequently, this leads to a significant improvement in the activity of the oxygen evolution reaction (OER). The synthesized Co2.5Fe0.5Se4 catalyst exhibits lower overpotential (η10 = 220 mV) and Tafel slope (41.2 mV dec−1), which is superior to the general commercial RuO2 benchmark. In addition, Co2.5Fe0.5Se4 also exhibits exceptional structural integrity and sustained operational longevity, with a durability of up to 280 h at 100 mA cmgeo−2. Impressively, the Pt/C∥Co2.5Fe0.5Se4 water electrolysis cell only requires a battery voltage of 1.67 V to provide a current density of 100 mA cmgeo−2 and has excellent long-term stability.

FeCoNiMgB high-entropy boride powder with a fluffy cotton structure and enhanced activity in the oxygen evolution reaction

Exploring efficient, low-cost electrocatalysts is critical for improving the efficiency of water splitting reactions. Noble-metal-based oxides exhibit high activities in the oxygen evolution reaction (OER). However, their high cost and the lack of natural resources hinder their practical application. Therefore, in this study, we successfully synthesized an FeCoNiMgB high-entropy boride powder via a facile chemical reduction method for use as an OER catalyst in an alkaline medium. The FeCoNiMgB powder, with an ultrathin fluffy cotton structure, exhibited an excellent OER catalytic performance, affording an overpotential of 268 mV at a current density of 10 mA/cm2 and a low Tafel slope of 42.9 mV/dec; this performance was superior to those of FeCoNiB, FeNiMgB, CoNiMgB, FeCoMgB, and commercial RuO2. The FeCoNiMgB powder also displayed remarkably stable catalytic properties for >72 h with no clear evidence of degradation. Finally, using theoretical calculations, the excellent OER performance of FeCoNiMgB was verified in terms of its adsorption and charge transfer energies and covalence. The performance and stability of FeCoNiMgB were equivalent or superior to those of several nanostructured catalysts, and thus, this study provided valuable insight into the design of efficient high-entropy boride materials.

Constructing Chainmail-Structured CoP/C Nanospheres as Highly Active Anodic Electrocatalysts for Oxygen Evolution Reaction.

Constructing highly active and noble metal-free electrocatalysts is significant for the anodic oxygen evolution reaction (OER). Herein, uniform carbon-coated CoP nanospheres (CoP/C) are developed by a direct impregnation coupling phosphorization approach. Importantly, CoP/C only takes a small overpotential of 230 mV at the current density of 10 mA cm-2 and displays a Tafel slope of 56.87 mV dec-1. Furthermore, the intrinsic activity of CoP/C is 21.44 times better than that of commercial RuO2 under an overpotential of 260 mV. In situ Raman spectroscopy studies revealed that a large number of generated Co-O and Co-OH species could facilitate the *OH adsorption, effectively accelerating the reaction kinetics. Meanwhile, the carbon shell with a large number of mesoporous pores acts as the chainmail of CoP, which could improve the active surface area of the catalyst and prevent the Co sites from oxidative dissolution. This work provides a facile and effective reference for the development of highly active and stable OER catalysts.

Locking the lattice oxygen in RuO2 to stabilize highly active Ru sites in acidic water oxidation

Ruthenium dioxide is presently the most active catalyst for the oxygen evolution reaction (OER) in acidic media but suffers from severe Ru dissolution resulting from the high covalency of Ru-O bonds triggering lattice oxygen oxidation. Here, we report an interstitial silicon-doping strategy to stabilize the highly active Ru sites of RuO2 while suppressing lattice oxygen oxidation. The representative Si-RuO2−0.1 catalyst exhibits high activity and stability in acid with a negligible degradation rate of ~52 μV h−1 in an 800 h test and an overpotential of 226 mV at 10 mA cm−2. Differential electrochemical mass spectrometry (DEMS) results demonstrate that the lattice oxygen oxidation pathway of the Si-RuO2−0.1 was suppressed by ∼95% compared to that of commercial RuO2, which is highly responsible for the extraordinary stability. This work supplied a unique mentality to guide future developments on Ru-based oxide catalysts’ stability in an acidic environment.

Ultrathin amorphous NaIrRuOx nanosheets with rich oxygen vacancies for efficient acidic water oxidation

Developing highly active and durable catalysts for H2O/O2 conversion is particularly important in water electrolyzers for renewable hydrogen energy. Herein, we prepared ultrathin amorphous NaIrRuOx nanosheets (NSs) with a thickness of 1.2 nm with a large number of oxygen vacancies using a simple molten salt method. The NaIrRuOx NSs exhibits a low overpotential (η10, 10 mA cm−2) of 214 mV, and 8.6 and 45.7 times enhanced mass activitynoble metal at 1.53 V vs. RHE, as compared to the commercial RuO2 and IrO2, respectively. Furthermore, the NaIrRuOx NSs shows excellent corrosion and oxidation resistance in acidic oxygen evolution reaction (OER), as confirmed by a negligible potential increase after 100 h of continuous electrolysis. In a homemade PEMWE, a membrane electrode using NaIrRuOx NSs as the anode catalyst can achieve cell voltages of 1.74 V at 1 A cm−2 and operate stably at 1 A cm−2 for 350 h. Theoretical calculations indicated that the intercalation of Na+ into IrRuOx weakens the adsorption strength of OER intermediates, thus reducing the energy consumption in the conversion from O* to OOH*, and thus significantly improving the OER performance.

Catalytic Activity and Electrochemical Stability of Ru1-xMxO2 (M = Zr, Nb, Ta): Computational and Experimental Study of the Oxygen Evolution Reaction.

We use computations and experiments to determine the effect of substituting zirconium, niobium, and tantalum within rutile RuO2 on the structure, oxygen evolution reaction (OER) mechanism and activity, and electrochemical stability. Calculated electronic structures altered by Zr, Nb, and Ta show surface regions of electron density depletion and accumulation, along with anisotropic lattice parameter shifts dependent on the substitution site, substituent, and concentration. Consistent with theory, X-ray photoelectron spectroscopy experiments show shifts in binding energies of O-2s, O-2p, and Ru-4d peaks due to the substituents. Experimentally, the substituted materials showed the presence of two phases with a majority phase that contains the metal substituent within the rutile phase and a second, smaller-percentage RuO2 phase. Our experimental analysis of OER activity shows Zr, Nb, and Ta substituents at 12.5 atom % induce lower activity relative to RuO2, which agrees with computing the average of all sites; however, Zr and Ta substitution at specific sites yields higher theoretical OER activity than RuO2, with Zr substitution suggesting an alternative OER mechanism. Metal dissolution predictions show the involvement of cooperative interactions among multiple surface sites and the electrolyte. Zr substitution at specific sites increases activation barriers for Ru dissolution, however, with Zr surface dissolution rates comparable to those of Ru. Experimental OER stability analysis shows lower Ru dissolution from synthesized RuO2 and Zr-substituted RuO2 compared to commercial RuO2 and comparable amounts of Zr and Ru dissolved from Zr-substituted RuO2, aligned with our calculations.

Enhanced electrochemical performance of MoSe2 nanosheets on CoAl- layered double hydroxide for oxygen evolution reaction

The design of high-efficiency electrocatalysts for water electrolysis has attracted much attention. A crucial half-reaction in electrochemical water splitting is the oxygen evolution reaction (OER), which suffers from sluggish reaction kinetics due to the high-energy barrier of the complex electron transfer process. This study presents a MoSe2@CoAl-layered double hydroxide (LDH) hybrid nanostructure prepared using the facile hydrothermal method and investigated as a potential OER electrocatalyst. Morphological analysis indicated that the MoSe2 formed in very thin nanosheet structures containing multiple defects on the LDH platelets, increasing the number of catalytic active sites. Compared with pristine MoSe2 and CoAl-LDH, the obtained MoSe2@CoAl-LDH catalyst exhibited enhanced electrocatalytic activity for the OER in an alkaline solution. The MoSe2@CoAl-LDH electrocatalyst showed an overpotential of 360 mV at a current density of 10 mA cm−2 and a small Tafel slope of 53 mV dec−1. In addition, it demonstrated good electrochemical stability. The MoSe2@CoAl-LDH exhibited a lower Tafel slope than commercial RuO2, indicating faster electron transfer on the MoSe2@CoAl-LDH electrode.

Interfacial Ru centers coupling with oxygen vacancies in VO-RuO2@CA hybrid aerogel boosts acidic water oxidation

The exploitation of highly active, cheap cost and durable electrocatalyst for acidic water oxidation reaction still presents a major technological and scientific challenge in proton exchange membrane water electrolysers (PEMWEs). Herein, a hybrid aerogel of oxygen defect-rich RuO2 nanoparticles coupling with carbon (VO-RuO2@CA) was designed to promote their activity and stability during acid water oxidation. The optimized VO-RuO2@CA achieves an ultralow overpotential of 207 mV at 10 mA cm−2 for acidic water oxidation and sustains a prominent long-term stability during the 30 h chronopotentiometry test in 0.5 M H2SO4. Furthermore, VO-RuO2@CA exhibits high mass activities of 186.5 mA mgRu−1 and TOF values of up to 2.07 s−1 at an overpotential of 300 mV, being 17.7 and 4.8 times higher than commercial RuO2, respectively. Theory calculations and experimental results verify that the oxygen vacancies (VO) could significantly weaken the binding energy of O* with respect to OOH* for the interfacial Ru centers between RuO2 and carbon, rendering the increase of the intrinsic water oxidation activity and resistance to over-oxidation for RuO2. This research provides a novel pathway to explore remarkably efficient 3D porous hybrid aerogel electrocatalysts toward anodic electrocatalysts applications in PEMWEs.

Tailored bimetallic synergy of iron–cobalt sulfide anchored to S-doped carbonized wood fiber for high-efficiency oxygen evolution reaction

Decoupling the scaling relation of intermediates is an effective strategy to improve the oxygen evolution reaction (OER) catalytic efficiency. Herein, S-doped carbon-confined Fe.92Co.08S nanoparticles (Fe.92Co.08S@SC) anchored to S-doped carbonized wood fiber (SCWF) are fabricated via simple synchronous carbonization and sulfidation. Due to the synergistic catalytic effect of bimetallic and the unique structural effect of the supported catalyst, Fe.92Co.08S@SC/SCWF exhibit excellent OER catalytic efficiency with an overpotential of 238 mV at 50 mA cm and stability up to 100 h. Furthermore, a high current density of 500 mA cm−2 at an overpotential of 281 mV was achieved. Theoretical calculations and electrochemical characterizations confirm that bimetallic synergies can accelerate the surface reconstruction of Fe.92Co.08S@SC with highly efficient OER activity. For zinc–air battery applications, Fe.92Co.08S@SC/SCWF exhibits superior power density and stability over commercial RuO2. This work provides insights into the preparation of supported electrocatalysts with bimetallic synergy for high-efficiency OER.

S-doped Yttrium Ruthenate Pyrochlore catalyst for Efficient Electrocatalytic Oxygen Evolution in Acidic Media

The sulfur-doped yttrium ruthenate pyrochlore catalysts was synthesized by simple hydrothermal method and exhibits excellent OER activity and stability under acidic conditions. Remarkably, the Y2Ru2O7S-0.17 catalyst reaches a current density of 10 mA cm−2 with only 237 mV and remains stable during 30 hours of electrolysis. In contrast, the original Y2Ru2O7 and commercial RuO2 require 282 mV and 365 mV, respectively. The introduction of sulfur into the internal lattice, replacing a portion of oxygen ions, creates vacancies that enhance the surface adsorption of oxygen. Furthermore, density functional theory calculations expose that S-doping alters the hybridization between the Ru 4d center and O 2p orbitals, significantly decreasing the energy barrier of the rate-determining step of the OER (O*--OOH*). Consequently, the intrinsic activity of the catalyst is greatly enhanced.

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.