Efficient Electrocatalyst For Oxygen Evolution Reaction Research Articles

Tailoring oxygen evolution performances of carbon nitride systems fabricated by electrophoresis through Ag and Au plasma functionalization

The strategic interest in the production of green hydrogen by sunlight-activated water splitting has stimulated significant efforts aimed at the implementation of active and cost-effective catalysts for the oxygen evolution reaction (OER), the overall process bottleneck. Herein, we report on an original fabrication route to OER electrocatalysts based on graphitic carbon nitride. In particular, the target systems were deposited on conductive glass substrates via a simple electrophoretic technique and functionalized with highly dispersed noble metals (Au, Ag or Au + Ag) in low amounts by radio frequency (RF)-sputtering under mild conditions. An advanced material characterization revealed the possibility of tailoring carbon nitride morphology as a function of the used precursor and of achieving a homogeneous spatial distribution of the functionalizing metals. The latter ranged from atomically dispersed (silver), to low-sized nanoaggregates (gold) or partially alloyed core–shell nanoparticles (gold+silver), with an intimate metal-nitride interfacial contact. Functional tests evidenced a remarkable sensitivity to Vis light even at low applied potentials, and photoelectrocatalytic performances directly dependent on the nature of metal species and on the features of the underlying carbon nitride deposit. These evidences, rationalized mainly on the basis of Schottky junctions and the possible concurrence of surface plasmon resonance (SPR), candidate the proposed strategy as a versatile route to cheap and efficient OER electrocatalysts for energy conversion.

Non-Calcined Layer-Pillared Mn0.5Zn0.5 Bimetallic-Organic Framework as a Promising Electrocatalyst for Oxygen Evolution Reaction.

Electrocatalytic generation of oxygen is of great significance for sustainable, clean, and efficient energy production. Multiple electron transfer in oxygen evolution reaction (OER) and its slow kinetics represent a serious hedge for efficient water splitting, requiring the design and development of advanced electrocatalysts with porous structures, high surface areas, abundant electroactive sites, and low overpotentials. These requisites are common for metal-organic frameworks (MOFs) and derived materials that are promising electrocatalysts for OER. The present work reports on the synthesis and full characterization of a heteroleptic 3D MOF, [Zn2(μ4-odba)2(μ-bpdh)]n·nDMF (Zn-MUM-1), assembled from 4,4'-oxydibenzoic acid and 2,5-bis(4-pyridyl)-3,4-diaza-2,4-hexadiene (bpdh). Besides, a series of heterometallic MnZn-MUM-1 frameworks (abbreviated as Mn0.5Zn0.5-MUM-1, Mn0.66Zn0.33-MUM-1, and Mn0.33Zn0.66-MUM-1) was also prepared, characterized, and used for the fabrication of working electrodes based on Ni foam (NF), followed by their exploration in OER. These noble-metal-free and robust electrocatalysts are stable and do not require pyrolysis or calcination while exhibiting better electrocatalytic performance than the parent Zn-MUM-1/NF electrode. The experimental results show that the Mn0.5Zn0.5-MUM-1/NF electrocatalyst features the best OER activity with a low overpotential (253 mV at 10 mA cm-2) and Tafel slope (73 mV dec-1) as well as significant stability after 72 h or 6000 cycles. These excellent results are explained by a synergic effect of two different metals present in the Mn-Zn MOF as well as improved charge and ion transfer, conductivity, and stability characteristics. The present study thus widens the application of heterometallic MOFs as prospective and highly efficient electrocatalysts for OER.

Room temperature, fast fabrication of square meter-sized oxygen evolution electrode toward industrial alkaline electrolyzer

NiFe-based electrode materials exhibit great promise for next-generation efficient oxygen evolution reaction (OER) electrocatalysts in alkaline medium, but they are difficult to be scaled up for large-area fabrication and are lack of robust research under real industrial conditions. Here we present a rapid, room-temperature sulfuration strategy that transforms stainless steel meshes into highly active and stable oxygen evolution electrodes. Such method is easy to be scaled up to produce square meter-sized stainless steel electrodes (1 m × 1 m) with NiFeCr-containing trimetal sulfides on the surface. In a standard three-electrode cell, the sulfurated stainless steel electrode exhibits 7.2 times higher OER activity than the corresponding stainless steel, and possesses remarkable catalytic stability for over 1000 h at the current density range of 100–200 mA cm−2. During the OER, the Cr and S species are demonstrated to be easily detached from the electrode surface, and the in situ formed γ-(Fe,Ni)OOH is found to be the electrocatalytic active phase. Furthermore, we integrate the sulfurated stainless steel electrode into an industrial alkaline electrolyzer as the anode (400 cm2). Our results demonstrate that the electrolyzer based on the sulfurated stainless steel electrode exhibits a better catalytic activity than the electrolyzer based on the Raney nickel electrode, a widely-adopted electrode in commercial water–alkali electrolyzers, and delivers a catalytic current of c.a. 300 mA cm–2 for over 120 h under the industrial catalytic conditions (30% KOH, 80 °C).

B, N, F tri-doped lignin-derived carbon nanofibers as an efficient metal-free bifunctional electrocatalyst for ORR and OER in rechargeable liquid/solid-state Zn-air batteries

The exploitation of cost-effective and high-efficiency bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is vital for the development of rechargeable metal-air batteries. Herein, B, N and F tri-doped lignin-based carbon porous nanofibers (BNF-LCFs) were prepared by electrospinning and pyrolysis without extra post-treatment using biomass lignin as carbon precursor, PVP as spinning additive, zinc borate as boron source, ammonium fluoride as fluorine source and partial nitrogen source. This method is simple, efficient, and environmentally friendly. Benefiting from the synergistic effect of B, N and F heteroatoms, large specific surface area and abundant defect sites, the BNF-LCF catalyst exhibits impressive bifunctional electrocatalytic performance towards ORR and OER with a small potential gap (ΔE) of 0.728 V. It outperforms the commercial Pt/C + RuO2 and most recently-reported non-metal carbon-based electrocatalysts. The liquid Zn-air batteries (ZABs) assembled with BNF-LCFs present a high open circuit potential of 1.536 V, a large specific capacity of 791.5 mAh g−1 and satisfactory cycling stability, superior to Pt + RuO2-based ZABs. Furthermore, the solid-state ZABs assembled with BNF-LCFs not only deliver excellent electrochemical performance, but also exhibit admirable mechanical flexibility and cycling stability, indicating favorable application prospects in flexible and wearable electronic devices.

Transformation of CoFe2O4 spinel structure into active and robust CoFe alloy/N-doped carbon electrocatalyst for oxygen evolution reaction

Electrochemical water splitting is an environmentally benign technology employed for H2 production; however, it is critically hampered by the sluggish kinetics of the oxygen evolution reaction (OER) at the positive electrode. In this work, nitrogen-doped carbon-coated CoFe electrocatalysts were synthesized via a three-step route comprising (1) hydrothermal reaction, (2) in-situ polymerization of dopamine and (3) carbonization. The effect of carbonized polydopamine on the overall physicochemical properties and electrochemical activity of CoFe catalysts was systematically studied. By controlling and optimizing the ratio of CoFe2O4 and dopamine contents, a transformation of the CoFe2O4 structure to CoFe alloy was observed. It was found that CoFe/NC30% (prepared with 30% dopamine) exhibits an excellent catalytic activity towards OER. A small overpotential of 340 mV was required to generate a current density of 10 mA cm−2 in a 1.0 M KOH electrolyte. More importantly, the CoFe/NC30% catalyst reflected exceptional durability for at least 24 h. This research sheds light on the development of affordable, highly efficient, and durable electrocatalysts for OER.

Time-dependent oxidation of graphite and cobalt oxide nanoparticles as electrocatalysts for the oxygen evolution reaction

• Co 3 O 4 /G OX was synthesized via a facile hydrothermal method for the OER. • Co 3 O 4 /G OX-10 catalyst showed the lowest overpotential of 250 mV at 10 mA cm −2 . • The optimal catalyst exhibited higher specific activity and turnover frequency. • Demonstrated improved electrical conductivity and small charge transfer resistance. • The optimal catalyst Exhibited excellent stability and durability. Water splitting is a promising way of producing hydrogen, but a highly efficient and durable electrocatalyst to accelerate the oxygen evolution reaction (OER) is required. In this study, we report cobalt oxide (Co 3 O 4 ) and oxidized graphite (G OX ) synthesized by a simple hydrothermal method to prepare a catalyst (Co 3 O 4 /G OX ) for the OER. Time-dependent oxidation of graphite (G) and Co 3 O 4 nanoparticles was observed by physical and electrochemical studies. The optimal catalyst (Co 3 O 4 /G OX-10 ) demonstrated the best catalytic OER performance with the lowest overpotential of 250 mV to reach 10 mA cm −2 and a small Tafel slope of 67 mV dec -1 , which is substantially smaller than that of pristine Co 3 O 4 and Co 3 O 4 /G. An efficient synergistic effect between Co 3 O 4 and G OX in the composite catalyst was observed compared to the individual catalysts. The optimal catalyst exhibited high specific activity (1.543 mA cm −2 ) and turnover frequency (0.474 s −1 ) compared to the other catalysts in this study. The high catalytic performance of the catalyst is attributed to the presence of oxygen functional groups, which induced a high electrochemical surface area, additional active site exposure, fast electron transfer, and enhanced dispersion of the catalyst. Thus, the synthesized Co 3 O 4 /G OX-10 catalyst can replace noble metals as an efficient OER electrocatalyst.

Enhanced OER performance of NiFeB amorphous alloys by surface self-reconstruction

The design and development of cost-effective and highly efficient oxygen evolution reaction (OER) electrocatalysts are urgently desirable during the water-splitting process. Here, NixFe80-xB20 (x = 70, 60, 50, 40, 30, hereafter referred to as NFB) amorphous alloys, with high mechanical strength, excellent corrosion resistance, and unique atomic structure, are fabricated as efficient water oxidation electrocatalysts in alkaline solutions. Ni40Fe40B20 amorphous ribbons achieve only 319 mV of overpotential at 10 mA·cm−2 with a Tafel slope of 56 mV dec−1 and exhibit excellent long-term stability for 24 h at 10 mA·cm−2 and 100 mA·cm−2 in 1 M KOH solution, which outperform the commercial RuO2 electrocatalyst. It is worth noting that the OER performance of NixFe80-xB20 amorphous electrocatalysts after long-term chronopotentiometry test displays more effectively, which can be ascribed to the surface construction. Meanwhile, the analysis of the morphology and structure of the electrocatalysts reveal that continuous oxidation during the OER process induces the structural reorganization on the surface of the electrocatalysts, which can enhance the electron transfer process and adsorption of the reaction intermediates to optimize the OER performance. This study provides a shred of evidence for surface self-reconstruction of NiFeB amorphous alloys electrocatalysts during the OER process and promotes the application of amorphous alloys as functional materials in the water-splitting field.

Tuning the electronic structure and inverse degree of inverse spinel ferrites by integrating samarium orthoferrite for efficient water oxidation

Optimized electronic configuration is of critical importance for developing active multimetallic electrocatalysts for oxygen evolution reaction (OER) but remains a challenge. Herein, we report a defect-rich samarium orthoferrite interfaced with samarium-doped nickel ferrite (SFO/Sm-NFO) as an efficient OER electrocatalyst. By multiple in situ ion-exchanges and calcination processes, the inverse degree and defects of SFO/Sm-NFO are effectively regulated to modulate the electronic structure at the interface. Our experimental and theoretical studies show that the Sm doping in NFO inverse spinels facilitates the rearrangement of Ni atoms to the octahedral sites that are the active site for OER. This enables highly enhanced OER activity as manifested by a low overpotential of 228 mV at 10 mA cm−2 (Tafel slope = 38.6 mV dec−1) with excellent stability at 500 and 1000 mA cm−2 for 100 h. This work provides useful insights into the rational designing of multimetallic nanohybrids for active and practical electrocatalysts.

Metal-Functionalized Hydrogels as Efficient Oxygen Evolution Electrocatalysts.

Conductive polymer hydrogels have large surface areas and electrical conductivities. Their properties can be further tailored by functionalizing them with metals and nonmetals. However, the potential applications of metal-functionalized hydrogels for electrocatalysis have rarely been investigated. In this work, we report the synthesis of transition-metal-functionalized polyaniline-phytic acid (PANI-PA) hydrogels that show efficient electrocatalytic activities for the oxygen evolution reaction (OER). Among the many transition metals studied, Fe is accommodated by the hydrogel the most due to the favorable affinity of the PA groups in the hydrogel for Fe. Meanwhile, those containing both Fe and Co are found to be the most effective electrocatalysts for OER. The most optimized such hydrogel, NF@Hgel-Fe0.3Co0.1, which is made using a solution that has a 3:1 ratio of Fe and Co, needs an overpotential of only 280 mV to catalyze OER in 1 M KOH solution with a current density of 10 mV cm-2. Furthermore, these metal-functionalized PANI-PA hydrogels can easily be loaded on the nickel foam or carbon cloth via a simple soak-and-dry method to generate free-standing electrodes. Overall, this work demonstrates a facile synthesis and fabrication of sustainable and efficient OER electrocatalysts and electrodes that are composed of easily processable hydrogels functionalized with earth-abundant transition metals.

Efficient oxygen evolution reaction electrocatalysts can boost green hydrogen electrosynthesis

In this issue of Chem Catalysis , Gohari-Bajestani et al. report on novel Fe-Co oxyfluoride catalysts that are able to surpass the state-of-the-art catalysts for the oxygen evolution reaction. Experimental and computational data suggest a cooperative effect between the Fe and Co metal sites responsible for the high catalytic activity. In this issue of Chem Catalysis , Gohari-Bajestani et al. report on novel Fe-Co oxyfluoride catalysts that are able to surpass the state-of-the-art catalysts for the oxygen evolution reaction. Experimental and computational data suggest a cooperative effect between the Fe and Co metal sites responsible for the high catalytic activity.

Corrosion engineering boosting bulk Fe50Mn30Co10Cr10 high-entropy alloy as high-efficient alkaline oxygen evolution reaction electrocatalyst

• The self-supported HEA catalyst was prepared by corrosion engineering. • Amorphous honeycomb nano-hydroxides are obtained on the HEA surface. • HEA-250Ni demonstrates the high OER activity and excellent stability. • The excellent performance is due to its special structure and diverse valence states. • Our findings open up a new avenue to prepare large-scale HEA as electrocatalysts. Oxygen evolution reaction (OER) is a critical process in electrocatalytic water splitting. However, the development of low-cost, highly efficient OER electrocatalysts by a simple method that can be used for industrial application on a large scale is still a huge challenge. Recently, high entropy alloy (HEA) has acquired extensive attention, which may provide answers to the current dilemma. Here, we report bulk Fe 50 Mn 30 Co 10 Cr 10 , which is prepared by 3D printing on a large scale, as electrocatalyst for OER with high catalytic performance. Especially, an easy approach, corrosion engineering, is adopted for the first time to build an active layer of honeycomb nanostructures on its surface, leading to ultrahigh OER performance with an overpotential of 247 mV to achieve a current density of 10 mA cm −2 , a low Tafel slope of 63 mV dec −1 , and excellent stability up to 60 h at 100 mA cm −2 in 1 M KOH. The excellent catalytic activity mainly originates from: (1) the binder-free self-supported honeycomb nanostructures and multi-component hydroxides, which improve intrinsic catalytic activity, provide rich active sites, and reduce interfacial resistance; and (2) the diverse valence states for multiple active sites to enhance the OER kinetics. Our findings show that corrosion engineering is a novel strategy to improve the bulk HEA catalytic performance. We expect that this work would open up a new avenue to fabricate large-scale HEA electrocatalysts by 3D printing and corrosion engineering for industrial applications.

High-performance seawater oxidation by a homogeneous multimetallic layered double hydroxide electrocatalyst

SignificanceSeawater is one of the most abundant resources on Earth. Direct electrolysis of seawater is a transformative technology for sustainable hydrogen production without causing freshwater scarcity. However, this technology is severely impeded by a lack of robust and active oxygen evolution reaction (OER) electrocatalysts. Here, we report a highly efficient OER electrocatalyst composed of multimetallic layered double hydroxides, which affords superior catalytic performance and long-term durability for high-performance seawater electrolysis. To the best of our knowledge, this catalyst is among the most active for OER and it advances the development of seawater electrolysis technology.

Surface engineering of MOFs as a route to cobalt phosphide electrocatalysts for efficient oxygen evolution reaction

Exploring efficient routes for the fabrication of promising transition metal phosphides electrocatalysts towards oxygen evolution reaction (OER) has become a top priority in the field of water-splitting technology. Herein, a cobalt phosphide (CoxP) electrocatalyst composed of high-density small Co2P/CoP nanoparticles homogeneously embedded in one-dimensional (1-D) carbon has been synthesized by using surface-engineered cobalt benzimidazole zeolitic imidazolate framework (ZIF-9) rods as a precursor. The surface engineering strategy employs melamine to modify ZIF-9 by constructing robust Co coordination sites on ZIF-9 surface through the coordination of Co with nitrogen donor sites in melamine. DFT calculations indicate that the surface engineering of ZIF-9 triggered by melamine occurs not only at coordinatively unsaturated Co sites but also at coordinatively saturated Co sites via a thermodynamically favored ligand exchange process between benzimidazole in ZIF-9 and melamine. Subsequent reaction with red phosphorus at high temperature affords a 1-D material having high-density of CoxP reactive sites and facilitated charge/mass transport, leading to an outstanding electrocatalytic activity for OER—even comparable to commercial RuO2—and excellent electrochemical durability. This scalable strategy involving surface engineering of MOFs represents a breakthrough in the synthesis of efficient OER electrocatalysts in water electrolyzer application.

Regulating multiscale structures of nickel-iron-based electrocatalysts for efficient water oxidation

The oxygen evolution reaction (OER) has been widely studied as an efficient process in energy conversion, yet the majority of studies focus on the strategies to boost the intrinsic activity of the catalyst, rather than considering the enhancement of its mass transfer ability. Herein, we produce efficient NiFe-based OER electrocatalysts with rich oxygen vacancies and abundant transport channels by an argon plasma-engraving strategy. Compared with pristine NiFe, the obtained best NiFe-plasma catalyst yields a 12.5-fold increased current density (from 80 to ∼1,000 mA cm −2 ) at an overpotential of 300 mV, surpassing most OER catalysts in alkaline solution. Density functional theory calculations disclose that the introduction of oxygen vacancies improve the intrinsic activity and electronic conductivity, while finite element method calculations demonstrate that the construction of catalytic interface and the creation of nanoscale transport channels facilitates mass transfer. • Plasma simultaneously produces oxygen vacancies and slit pores on NiFe • FEM calculation illustrates that the slit pores can facilitate mass transport • The obtained NiFe-plasma catalyst yields a 12.5-fold increased current density Wang et al. prepare efficient NiFe-based OER electrocatalysts with abundant oxygen vacancies and transport channels by plasma engraving. Owing to the synergistic effect between high intrinsic catalytic activity and preferable mass transfer ability, the NiFe-P-200-15 exhibits a small overpotential of 302 mV to reach 1.0 A cm −2 in alkaline electrolyte.

Morphology-Dependent Electrocatalytic Performance of a Two-Dimensional Nickel-Iron MOF for Oxygen Evolution Reaction.

Developing highly efficient, low-cost, and durable oxygen evolution reaction (OER) electrocatalysts is extraordinarily desirable for achieving clean and sustainable hydrogen energy. Metal-organic frameworks (MOFs) are emerging as attractive candidates for OER electrocatalysts. Herein, a two-dimensional Fe-Ni MOF of Fe(py)2Ni(CN)4 (py = pyridine) is synthesized controllably to generate various nanostructures, including nanoboxes, nanocubes, nanoplates, and nanosheets. Since different morphologies expose different active crystal planes and generate disparate intrinsic active sites, these nanostructures exhibit obviously different electrocatalytic activities. Particularly, the nanoboxes with a hollow structure display superior electrocatalytic activity and stability for OER due to greater active surface area and higher intrinsic activity of the exposed crystal planes, delivering a low overpotential of 285 mV at 10 mA cm-2 and a small Tafel value of 50.9 mV dec-1 in a 1.0 M KOH solution. The morphology-dependent electrocatalytic properties demonstrated in this work provide an efficient strategy to optimize MOF precatalysts for electrochemical energy storage and conversion.

In situ confined vertical growth of Co2.5Ni0.5Si2O5(OH)4 nanoarrays on rGO for an efficient oxygen evolution reaction

Rational design of oxygen evolution reaction (OER) catalysts at low cost would greatly benefit the economy. Taking advantage of earth-abundant elements Si, Co and Ni, we produce a unique-structure where cobalt-nickel silicate hydroxide [Co2.5Ni0.5Si2O5(OH)4] is vertically grown on a reduced graphene oxide (rGO) support (CNS@rGO). This is developed as a low-cost and prospective OER catalyst. Compared to cobalt or nickel silicate hydroxide@rGO (CS@rGO and NS@rGO, respectively) nanoarrays, the bimetal CNS@rGO nanoarray exhibits impressive OER performance with an overpotential of 307 ​mV@10 ​mA ​cm−2. This value is higher than that of CS@rGO and NS@rGO. The CNS@rGO nanoarray has an overpotential of 446 ​mV@100 ​mA ​cm−2, about 1.4 times that of the commercial RuO2 electrocatalyst. The achieved OER activity is superior to the state-of-the-art metal oxides/hydroxides and their derivatives. The vertically grown nanostructure and optimized metal-support electronic interactions play an indispensable role for OER performance improvement, including a fast electron transfer pathway, short proton/electron diffusion distance, more active metal centers, as well as optimized dual-atomic electron density. Taking advantage of interlay chemical regulation and the in-situ growth method, the advanced-structural CNS@rGO nanoarrays provide a new horizon to the rational and flexible design of efficient and promising OER electrocatalysts.

One step synthesis of Co-Ni bimetallic organic frameworks as a highly active and durable electrocatalyst for efficient water oxidation

As a half-reaction in the water decomposition, the oxygen evolution reaction (OER) has limited the development and practical application of water splitting due to the kinetic speed and high overpotential. Therefore, it still exists a challenge to exploit high-performance and durable electrocatalysts for OER. Herein, a one-step hydrothermal approach was designed to prepare Co-Ni bimetallic organic frameworks (MOFs) on nickel foam (NF) substrate as a highly efficient electrocatalyst for OER under alkaline conditions. The prepared MIL-53(Co-Ni)/NF has excellent OER catalytic activity, which requires only an overpotential of 197 mV to achieve 20 mA cm−2. The proposed electrocatalyst exhibits long-term durability (>60 h) and a high turnover frequency (TOF) of 0.2806 mol O2 s−1 at 350 mV. Systematic study revealed that the coordination between Co-Ni played a significant role to improve OER performance. The present results demonstrated that bimetallic organic frameworks could be utilized to fabricate promising water-oxidation catalysts in energy conversion.

High efficiency electrocatalyst of LaNiO3@LaCoO3 nanoparticles on oxygen-evolution reaction

It is urgent to develop high-efficiency, stable and inexpensive electrocatalysts for oxygen evolution reaction (OER). In this work, we investigate the electrocatalystic properties of perovskite-type hybrid LaNiO3@LaCoO3 nanoparticle composites. At a current density of 10 mA/cm2, it shows a low overpotential of 400 mV, a small Tafel slope of 120.3 mV/dec. In addition, it also demonstrates excellent electrochemical stability with almost no drop of current density after operating for 20 h, which is superior to that of their individual counterparts. This work shows that the current perovskite composites will become an important component of efficient non-noble metal-based OER electrocatalysts.

Silver decorated hydroxides electrocatalysts for efficient oxygen evolution reaction

Electrocatalysts play a pivotal role in electrochemical water splitting, where the development of efficient oxygen evolution reaction (OER) electrocatalysts remains challenging. Here, we report a facile one-step blending approach to synthesize efficient and durable OER electrocatalysts of silver decorated hydroxides (Ag@hydroxides). The general efficacy of this methodology is demonstrated in five hydroxides, in form of powders or self-supported electrodes. The decoration of Ag lowers the overpotentials by 41–56 mV, rendering Ag@NiFe LDH among the most active OER catalysts. It requires an overpotential of 246 mV only to deliver a current density of 10 mA cm−2. Under industrial electrolysis conditions (30 wt% KOH and 80 °C), the cell voltage is 1.76 V for 500 mA cm−2. It is 270 mV lower than the intact nickel mesh, corresponding to a 9% improvement in the energy conversion efficiency. Furthermore, by combining spectroscopic analysis and theoretical calculation we unravel that the strong interfacial charge transfer is the root cause for the promoting catalytic activity, where the binding energies of catalytic intermediates are optimized. This work provides a facile and ease-to-scale-up approach for the synthesis of efficient and durable electrocatalysts and demonstrates the power of regulating the interface in improving electrocatalytic kinetics.

Ordered macroporous design of sacrificial Co/VN nano-heterojunction as bifunctional oxygen electrocatalyst for rechargeable zinc-air batteries

• •Ordered macroporous design of sacrificial Co/VN nano-heterojunction was developed. • •VN act as sacrificial OER promoter converting Co into active Co 3 O 4 /CoOOH species. • •The Co/VN electrode exhibits excellent performance in rechargeable zinc-air batteries. The development of efficient oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) bifunctional electrocatalysts is essential for rechargeable zinc-air batteries (ZABs). Herein, an ORR/OER bifunctional pre-catalyst consists of Co/VN heterojunction supported by N-doped carbon (NC) with three-dimensionally ordered macroporous (3DOM) architecture was fabricated. The VN was introduced as sacrificial promoter to facilitate the oxidization and self-reconstruction of Co into Co 3 O 4 and CoOOH during OER process, which acts as the real active OER component. On the other hand, the Co-decorated N-doped carbon is the active species for ORR reaction. Meanwhile, the 3DOM structure design also provides a large specific surface area and exposes rich active sites. Benefiting from those advantages, the Co/VN@NC exhibits good activity and stability towards ORR and OER reactions comparable with commercial catalysts. Moreover, density functional theory calculations confirmed that Co 3 O 4 and CoOOH exhibit higher adsorption energy for OH – and present an exothermic reaction in the OER process, which is beneficial to OER reaction. The ZABs using Co/VN@NC as bifunctional catalyst exhibits a high specific capacity of 775.68 mAh g −1 under 10 mA cm −2 and ultralong charge–discharge cycle life about 200 h at 20 mA cm −2 . This work provides a new strategy of using sacrificial heterojunction for the development of efficient and durable bifunctional oxygen electrocatalyst.