Graphene Composites with Cobalt Sulfide: Efficient Trifunctional Electrocatalysts for Oxygen Reversible Catalysis and Hydrogen Production in the Same Electrolyte

Nitrogen and sulfur‐codoped graphene composites with Co₉S₈ (NS/rGO‐Co) are synthesized by facile thermal annealing of graphene oxides with cobalt nitrate and thiourea in an ammonium atmosphere. Significantly, in 0.1 m KOH aqueous solution the best sample exhibits an oxygen evolution reaction (OER) activity that is superior to that of benchmark RuO₂ catalysts, an oxygen reduction reaction (ORR) activity that is comparable to that of commercial Pt/C, and an overpotential of only ?0.193 V to reach 10 mA cm^?2 for hydrogen evolution reaction (HER). With this single catalyst for oxygen reversible electrocatalysis, a potential difference of only 0.700 V is observed in 0.1 m KOH solution between the half‐wave potential in ORR and the potential to reach 10 mA cm^?2 in OER; in addition, an overpotential of only 450 mV is needed to reach 10 mA cm^?2 for full water splitting in the same electrolyte. The present trifunctional catalytic activities are markedly better than leading results reported in recent literature, where the remarkable trifunctional activity is attributed to the synergetic effects between N,S‐codoped rGO, and Co₉S₈ nanoparticles. These results highlight the significance of deliberate structural engineering in the preparation of multifunctional electrocatalysts for versatile electrochemical reactions.     

Simultaneously Integrating Single Atomic Cobalt Sites and Co9S8 Nanoparticles into Hollow Carbon Nanotubes as Trifunctional Electrocatalysts for Zn–Air Batteries to Drive Water Splitting

The development of rechargeable metal–air batteries and water electrolyzers are highly constrained by electrocatalysts for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). However, the construction of efficient trifunctional electrocatalysts for ORR/OER/HER are highly desirable yet challenging. Herein, hollow carbon nanotubes integrated single cobalt atoms with Co₉S₈ nanoparticles (CoSA + Co₉S₈/HCNT) are fabricated by a straightforward in situ self‐sacrificing strategy. The structure of the CoSA + Co₉S₈/HCNT are verified by X‐ray absorption spectroscopy and aberration‐corrected scanning transmission electron microscopy. Theoretical calculations and experimental results embrace the synergistic effects between Co₉S₈ nanoparticles and single cobalt atoms through optimizing the electronic configuration of the CoN₄ active sites to lower the reaction barrier and facilitating the ORR, OER, and HER simultaneously. Consequently, rechargeable liquid and all‐solid‐state flexible Zn–air batteries based on CoSA + Co₉S₈/HCNT exhibit remarkable stability and excellent power density of 177.33 and 51.85 mW cm^?2, respectively, better than Pt/C + RuO₂ counterparts. Moreover, the as‐fabricated Zn–air batteries can drive an overall water splitting device assembled with CoSA + Co₉S₈/HCNT and achieve a current density of 10 mA cm^?2 at a low voltage of 1.59 V, also superior to Pt/C + RuO₂. Therefore, this work presents a promising approach to an efficient trifunctional electrocatalyst toward practical applications.     

One‐Step Route Synthesized Co2P/Ru/N‐Doped Carbon Nanotube Hybrids as Bifunctional Electrocatalysts for High‐Performance Li–O2 Batteries

The large‐scale commercial application of lithium–oxygen batteries (LOBs) is overwhelmed by the sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) associated with insoluble and insulated Li₂O₂. Herein, an elaborate design on a highly catalytic LOBs cathode constructed by N‐doped carbon nanotubes (CNT) with in situ encapsulated Co₂P and Ru nanoparticles is reported. The homogeneously dispersed Co₂P and Ru catalysts can effectively modulate the formation and decomposition behavior of Li₂O₂ during discharge/charge processes, ameliorating the electronically insulating property of Li₂O₂ and constructing a homogenous low‐impedance Li₂O₂/catalyst interface. Compared with Co/CNT and Ru/CNT electrodes, the Co₂P/Ru/CNT electrode delivers much higher oxygen reduction triggering onset potential and higher ORR and OER peak current and integral areas, showing greatly improved ORR/OER kinetics due to the synergistic effects of Co₂P and Ru. Li–O₂ cells based on the Ru/Co₂P/CNT electrode demonstrate improved ORR/OER overpotential of 0.75 V, excellent rate capability of 12 800 mAh g^?1 at 1 A g^?1, and superior cycle stability for more than 185 cycles under a restricted capacity of 1000 mAh g^?1 at 100 mA g^?1. This work paves an exciting avenue for the design and construction of bifunctional catalytic cathodes by coupling metal phosphides with other active components in LOBs.     

Zirconium‐Regulation‐Induced Bifunctionality in 3D Cobalt–Iron Oxide Nanosheets for Overall Water Splitting

The design of high‐efficiency non‐noble bifunctional electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is paramount for water splitting technologies and associated renewable energy systems. Spinel‐structured oxides with rich redox properties can serve as alternative low‐cost OER electrocatalysts but with poor HER performance. Here, zirconium regulation in 3D CoFe₂O₄ (CoFeZr oxides) nanosheets on nickel foam, as a novel strategy inducing bifunctionality toward OER and HER for overall water splitting, is reported. It is found that the incorporation of Zr into CoFe₂O₄ can tune the nanosheet morphology and electronic structure around the Co and Fe sites for optimizing adsorption energies, thus effectively enhancing the intrinsic activity of active sites. The as‐synthesized 3D CoFeZr oxide nanosheet exhibits high OER activity with small overpotential, low Tafel slope, and good stability. Moreover, it shows unprecedented HER activity with a small overpotential of 104 mV at 10 mA cm^?2 in alkaline media, which is better than ever reported counterparts. When employing the CoFeZr oxides nanosheets as both anode and cathode catalysts for overall water splitting, a current density of 10 mA cm^?2 is achieved at the cell voltage of 1.63 V in 1.0 m KOH.     

Colloidal Cobalt Phosphide Nanocrystals as Trifunctional Electrocatalysts for Overall Water Splitting Powered by a Zinc–Air Battery

Highly efficient and stable electrocatalysts, particularly those that are capable of multifunctionality in the same electrolyte, are in high demand for the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). In this work, highly monodisperse CoP and Co₂P nanocrystals (NCs) are synthesized using a robust solution‐phase method. The highly exposed (211) crystal plane and abundant surface phosphide atoms make the CoP NCs efficient catalysts toward ORR and HER, while metal‐rich Co₂P NCs show higher OER performance owing to easier formation of plentiful Co₂P@COOH heterojunctions. Density functional theory calculation results indicate that the desorption of OH* from cobalt sites is the rate‐limiting step for both CoP and Co₂P in ORR and that the high content of phosphide can lower the reaction barrier. A water electrolyzer constructed with a CoP NC cathode and a Co₂P NC anode can achieve a current density of 10 mA cm^?2 at 1.56 V, comparable even to the noble metal‐based Pt/C and RuO₂/C pair. Furthermore, the CoP NCs are employed as an air cathode in a primary zinc–air battery, exhibiting a high power density of 62 mW cm^?2 and good stability.     

Bifunctional Transition Metal Hydroxysulfides: Room‐Temperature Sulfurization and Their Applications in Zn–Air Batteries

Bifunctional electrocatalysis for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) constitutes the bottleneck of various sustainable energy devices and systems like rechargeable metal–air batteries. Emerging catalyst materials are strongly requested toward superior electrocatalytic activities and practical applications. In this study, transition metal hydroxysulfides are presented as bifunctional OER/ORR electrocatalysts for Zn–air batteries. By simply immersing Co‐based hydroxide precursor into solution with high‐concentration S^2?, transition metal hydroxides convert to hydroxysulfides with excellent morphology preservation at room temperature. The as‐obtained Co‐based metal hydroxysulfides are with high intrinsic reactivity and electrical conductivity. The electron structure of the active sites is adjusted by anion modulation. The potential for 10 mA cm^?2 OER current density is 1.588 V versus reversible hydrogen electrode (RHE), and the ORR half‐wave potential is 0.721 V versus RHE, with a potential gap of 0.867 V for bifunctional oxygen electrocatalysis. The Co₃FeS_1.5(OH)₆ hydroxysulfides are employed in the air electrode for a rechargeable Zn–air battery with a small overpotential of 0.86 V at 20.0 mA cm^?2, a high specific capacity of 898 mAh g^?1, and a long cycling life, which is much better than Pt and Ir‐based electrocatalyst in Zn–air batteries.     

Single Ni Atoms and Clusters Embedded in N‐Doped Carbon “Tubes on Fibers” Matrix with Bifunctional Activity for Water Splitting at High Current Densities

Among the bifunctional catalysts for water splitting, recently emerged transition‐metal single‐atom catalysts are theoretically considered to possess high potential, while the experimental activity is not satisfactory yet. Herein, an exceptionally efficient trifunctional metal–nitrogen–carbon (M–N–C) catalyst electrode, composed of a hierarchical carbon matrix embedding isolated nickel atoms with nickel–iron (NiFe) clusters, is presented. 1D microfibers and nanotubes grow sequentially from 2D nanosheets as sacrificial templates via two stages of solution‐ and solid‐phase reactions to form a 1D hierarchy. Exceptionally efficient bifunctional activity with an overpotential of only 13 mV at 10 mA cm^?2 toward hydrogen evolution reaction (HER) and an overpotential of 210 mV at 30 mA cm^?2 toward oxygen evolution reaction (OER) is obtained, surpassing each monofunctional activity ever reported. More importantly, an overpotential of only 126 and 326 mV is required to drive 500 mA cm^?2 toward the HER and OER, respectively. For the first time, industrial‐scale water splitting with two bifunctional catalyst electrodes with a current density of 500 mA cm^?2 at a potential of 1.71 V is demonstrated. Lastly, trifunctional catalytic activity including oxygen reduction reaction is also proven with a half‐wave potential at 0.848 V.     

ZIF‐8/ZIF‐67‐Derived Co‐Nx‐Embedded 1D Porous Carbon Nanofibers with Graphitic Carbon‐Encased Co Nanoparticles as an Efficient Bifunctional Electrocatalyst

Herein, an approach is reported for fabrication of Co‐N_x‐embedded 1D porous carbon nanofibers (CNFs) with graphitic carbon‐encased Co nanoparticles originated from metal–organic frameworks (MOFs), which is further explored as a bifunctional electrocatalyst for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Electrochemical results reveal that the electrocatalyst prepared by pyrolysis at 1000 °C (CoNC‐CNF‐1000) exhibits excellent catalytic activity toward ORR that favors the four‐electron ORR process and outstanding long‐term stability with 86% current retention after 40 000 s. Meanwhile, it also shows superior electrocatalytic activity toward OER, reaching a lower potential of 1.68 V at 10 mA cm^?2 and a potential gap of 0.88 V between the OER potential (at 10 mA cm^?2) and the ORR half‐wave potential. The ORR and OER performance of CoNC‐CNF‐1000 have outperformed commercial Pt/C and most nonprecious‐metal catalysts reported to date. The remarkable ORR and OER catalytic performance can be mainly attributable to the unique 1D structure, such as higher graphitization degree beneficial for electronic mobility, hierarchical porosity facilitating the mass transport, and highly dispersed CoN_xC active sites functionalized carbon framework. This strategy will shed light on the development of other MOF‐based carbon nanofibers for energy storage and electrochemical devices.     

Nickel Diselenide Ultrathin Nanowires Decorated with Amorphous Nickel Oxide Nanoparticles for Enhanced Water Splitting Electrocatalysis

Well‐designed hybrid materials based on noble metal‐free elements have great potential to generate hydrogen (H₂) and oxygen (O₂) sustainably via overall water splitting for developing practical energy‐related technologies. Herein, an accessible method is presented to synthesize nickel diselenide (NiSe₂) ultrathin nanowires decorated with amorphous nickel oxide nanoparticles (NiO_x NPs) as multifunctional electrocatalysts (NSWANs) for hydrogen and oxygen evolution reaction (HER and OER). The NSWANs exhibit quite low HER and OER overpotentials of 174 and 295 mV, respectively, holding the current density of 20 mA cm^?2 for 24 h continuous operations in alkaline media. Meanwhile, a cell voltage of 1.547 V at the current density of 10 mA cm^?2 for overall water splitting has been achieved by the NSWANs for the practical application, which could maintain fascinating activity of 20 mA cm^?2 for 72 h without degradation. The decorated NiO_x NPs not only prevent the NiSe₂ from further oxidation but also expose requisite active sites for electrocatalytic process. It is believed that this study may provide a valuable strategy to design high‐efficiency electrocatalysts and expand the applications of selenide‐based materials.     

Assembling Ultrasmall Copper‐Doped Ruthenium Oxide Nanocrystals into Hollow Porous Polyhedra: Highly Robust Electrocatalysts for Oxygen Evolution in Acidic Media

Here, a facile and novel strategy for the preparation of Cu‐doped RuO₂ hollow porous polyhedra composed of ultrasmall nanocrystals through one‐step annealing of a Ru‐exchanged Cu‐BTC derivative is reported. Owing to the optimized surface configuration and altered electronic structure, the prepared catalyst displays a remarkable oxygen evolution reaction (OER) performance with low overpotential of 188 mV at 10 mA cm^?2 in acidic electrolyte, an ultralow Tafel slope of 43.96 mV dec^?1, and excellent stability in durability testing for 10 000 cycles, and continuous testing of 8 h at a current density of 10 mA cm^?2. Density functional theory calculations reveal that the highly unsaturated Ru sites on the high‐index facets can be oxidized gradually and reduce the energy barrier of rate‐determining steps. On the other hand, the Cu dopants can alter the electronic structures so as to further improve the intrinsic OER activity.     

Metallic Metastable Hybrid 1T′/1T Phase Triggered Co,P?SnS2 Nanosheets for High Efficiency Trifunctional Electrocatalyst

The development of trifunctional electrocatalyst for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) with deeply understanding the mechanism to enhance the electrochemical performance is still a challenging task. In this work, the distorted metastable hybrid-phase induced 1T′/1T Co,P SnS₂ nanosheets on carbon cloth (1T′/1T Co,P SnS₂@CC) is prepared and examined. The density functional theoretical (DFT) calculation suggests that the distorted 1T′/1T Co,P SnS₂ can provide excellent conductivity and strong hydrogen adsorption ability. The electronic structure tuning and enhancement mechanism of electrochemical performance are investigated and discussed. The optimal 1T′/1T Co,P SnS₂@CC catalyst exhibits low overpotential of ≈94 and 219.7 mV at 10 mA cm⁻² for HER and OER, respectively. Remarkably, the catalyst exhibits exceptional ORR activity with small onset potential value (≈0.94 V) and half-wave potential (≈0.87 V). Most significantly, the 1T′/1T Co,P SnS₂||Co,P SnS₂ electrolyzer required small cell voltages of ≈1.53, 1.70, and 1.82 V at 10, 100, and 400 mA cm⁻², respectively, which are better than those of state-of-the-art Pt-C||RuO₂ (≈1.56 and 1.84 V at 10 and 100 mA cm⁻²). The present study suggests a new approach for the preparation of large-scalable, high performance hierarchical 3D next-generation trifunctional electrocatalysts.     

Amorphous Bimetallic Oxide–Graphene Hybrids as Bifunctional Oxygen Electrocatalysts for Rechargeable Zn–Air Batteries

Metal oxides of earth‐abundant elements are promising electrocatalysts to overcome the sluggish oxygen evolution and oxygen reduction reaction (OER/ORR) in many electrochemical energy‐conversion devices. However, it is difficult to control their catalytic activity precisely. Here, a general three‐stage synthesis strategy is described to produce a family of hybrid materials comprising amorphous bimetallic oxide nanoparticles anchored on N‐doped reduced graphene oxide with simultaneous control of nanoparticle elemental composition, size, and crystallinity. Amorphous Fe_0.5Co_0.5O_x is obtained from Prussian blue analog nanocrystals, showing excellent OER activity with a Tafel slope of 30.1 mV dec^?1 and an overpotential of 257 mV for 10 mA cm^?2 and superior ORR activity with a large limiting current density of ?5.25 mA cm^?2 at 0.6 V. A fabricated Zn–air battery delivers a specific capacity of 756 mA h g_Zn^?1 (corresponding to an energy density of 904 W h kg_Zn^?1), a peak power density of 86 mW cm^?2 and can be cycled over 120 h at 10 mA cm^?2. Other two amorphous bimetallic, Ni_0.4Fe_0.6O_x and Ni_0.33Co_0.67O_x , are also produced to demonstrate the general applicability of this method for synthesizing binary metal oxides with controllable structures as electrocatalysts for energy conversion.     

3D Nitrogen‐Anion‐Decorated Nickel Sulfides for Highly Efficient Overall Water Splitting

Developing non‐noble‐metal electrocatalysts with high activity and low cost for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is of paramount importance for improving the generation of H₂ fuel by electrocatalytic water‐splitting. This study puts forward a new N‐anion‐decorated Ni₃S₂ material synthesized by a simple one‐step calcination route, acting as a superior bifunctional electrocatalyst for the OER/HER for the first time. The introduction of N anions significantly modifies the morphology and electronic structure of Ni₃S₂, bringing high surface active sites exposure, enhanced electrical conductivity, optimal HER Gibbs free‐energy (ΔG_H*), and water adsorption energy change (ΔG_H2O*). Remarkably, the obtained N‐Ni₃S₂/NF 3D electrode exhibits extremely low overpotentials of 330 and 110 mV to reach a current density of 100 and 10 mA cm^?2 for the OER and HER in 1.0 m KOH, respectively. Moreover, an overall water‐splitting device comprising this electrode delivers a current density of 10 mA cm^?2 at a very low cell voltage of 1.48 V. Our finding introduces a new way to design advanced bifunctional catalysts for water splitting.     

Construction of Defect‐Rich Ni‐Fe‐Doped K0.23MnO2 Cubic Nanoflowers via Etching Prussian Blue Analogue for Efficient Overall Water Splitting

Designing elaborate nanostructures and engineering defects have been promising approaches to fabricate cost‐efficient electrocatalysts toward overall water splitting. In this work, a controllable Prussian‐blue‐analogue‐sacrificed strategy followed by an annealing process to harvest defect‐rich Ni‐Fe‐doped K_0.23MnO₂ cubic nanoflowers (Ni‐Fe‐K_0.23MnO₂ CNFs‐300) as highly active bifunctional catalysts for oxygen and hydrogen evolution reactions (OER and HER) is reported. Benefiting from many merits, including unique morphology, abundant defects, and doping effect, Ni‐Fe‐K_0.23MnO₂ CNFs‐300 shows the best electrocatalytic performances among currently reported Mn oxide‐based electrocatalysts. This catalyst affords low overpotentials of 270 (320) mV at 10 (100) mA cm^?2 for OER with a small Tafel slope of 42.3 mV dec^?1, while requiring overpotentials of 116 and 243 mV to attain 10 and 100 mA cm^?2 for HER respectively. Moreover, Ni‐Fe‐K_0.23MnO₂ CNFs‐300 applied to overall water splitting exhibits a low cell voltage of 1.62 V at 10 mA cm^?2 and excellent durability, even superior to the Pt/C||IrO₂ cell at large current density. Density functional theory calculations further confirm that doping Ni and Fe into the crystal lattice of δ‐MnO₂ can not only reinforce the conductivity but also reduces the adsorption free‐energy barriers on the active sites during OER and HER.     

Efficient Bifunctional Catalytic Electrodes with Uniformly Distributed NiN2 Active Sites and Channels for Long‐Lasting Rechargeable Zinc–Air Batteries

Freestanding bifunctional electrodes with outstanding oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) properties are of great significance for zinc–air batteries, attributed to the avoided use of organic binder and strong adhesion with substrates. Herein, a strategy is developed to fabricate freestanding bifunctional electrodes from the predeposited nickel nanoparticles (Ni‐NCNT) on carbon fiber paper. The steric effect of monodispersed SiO₂ nanospheres limits the configuration of carbon atoms forming 3D interconnected nanotubes with uniformly distributed NiN₂ active sites. The bifunctional electrodes (Ni‐NCNT) demonstrate ideal ORR and OER properties. The zinc–air batteries assembled with Ni‐NCNT directly exhibit extremely outstanding long term stability (2250 cycles with 10 mA cm^?2 charge/discharge current density) along with high power density of 120 mV cm^?2 and specific capacity of 834.1 mA h g^?1. This work provides a new view to optimize the distribution of active sites and the electrode structure.     

Surface Oxidation of AuNi Heterodimers to Achieve High Activities toward Hydrogen/Oxygen Evolution and Oxygen Reduction Reactions

Although much attention has been paid to the exploration of highly active electrocatalysts, especially catalysts for hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), the development of multifunctional catalysts remains a challenge. Here, we utilize AuNi heterodimers as the starting materials to achieve high activities toward HER, OER and ORR. The HER and ORR activities in an alkali environment are similar to those of Pt catalysts, and the OER activity is very high and better than that of commercial IrO₂. Both the experimental and calculated results suggest that the surface oxidation under oxidative conditions is the main reason for the different activities. The NiO/Ni interface which exists in the as‐synthesized heterodimers contributes to high HER activity, the Ni(OH)₂‐Ni‐Au interface and the surface Ni(OH)₂ obtained in electrochemical conditons gives rise to promising ORR and OER activities, respectively. As a comparison, a Au@Ni core‐shell structure is also synthesized and examined. The core‐shell structure shows lower activities for HER and OER than the heterodimers, and reduces O₂ selectively to H₂O₂. The work here allows for the development of a method to design multifunctional catalysts via the partial oxidation of a metal surface to create different active centers.     

Electronic Modulation of Nickel Disulfide toward Efficient Water Electrolysis

Developing highly efficient earth‐abundant nickel‐based compounds is an important step to realize hydrogen generation from water. Herein, the electronic modulation of the semiconducting NiS₂ by cation doping for advanced water electrolysis is reported. Both theoretical calculations and temperature‐dependent resistivity measurements indicate the semiconductor‐to‐conductor transition of NiS₂ after Cu incorporation. Further calculations also suggest the advantages of Cu dopant to cathodic water electrolysis by bringing Gibbs free energy of H adsorption at both Ni sites and S sites much closer to zero. It is noteworthy that water dissociation on Cu‐doped NiS₂ (Cu‐NiS₂) surface is even more favorable than those on NiS₂ and Pt(111). Thus, the prepared Cu‐NiS₂ shows noticeably improved performance toward alkaline hydrogen and oxygen evolution reactions (HER and OER). Specifically, it requires merely 232 mV OER overpotential to drive 10 mA cm^?2; in parallel with Tafel slopes of 46 mV dec^?1. Regarding HER, an onset overpotential of only 68 mV is achieved. When integrated as both electrodes for water electrolysis, Cu‐NiS₂ needs only 1.64 V to drive 10 mA cm^?2, surpassing the state‐of‐the‐art Ir/C–Pt/C couple (1.71 V). This work opens up an avenue to engineer low‐cost and earth‐abundant catalysts performing on par with the noble‐metal‐based one for water splitting.     

Ultrathin Cobalt Oxide Layers as Electrocatalysts for High‐Performance Flexible Zn–Air Batteries

Synergistic improvements in the electrical conductivity and catalytic activity for the oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) are of paramount importance for rechargeable metal–air batteries. In this study, one‐nanometer‐scale ultrathin cobalt oxide (CoO_x) layers are fabricated on a conducting substrate (i.e., a metallic Co/N‐doped graphene substrate) to achieve superior bifunctional activity in both the ORR and OER and ultrahigh output power for flexible Zn–air batteries. Specifically, at the atomic scale, the ultrathin CoO_x layers effectively accelerate electron conduction and provide abundant active sites. X‐ray absorption spectroscopy reveals that the metallic Co/N‐doped graphene substrate contributes to electron transfer toward the ultrathin CoO_x layer, which is beneficial for the electrocatalytic process. The as‐obtained electrocatalyst exhibits ultrahigh electrochemical activity with a positive half‐wave potential of 0.896 V for ORR and a low overpotential of 370 mV at 10 mA cm^?2 for OER. The flexible Zn–air battery built with this catalyst exhibits an ultrahigh specific power of 300 W g_cat ^?1, which is essential for portable devices. This work provides a new design pathway for electrocatalysts for high‐performance rechargeable metal–air battery systems.     

Interfacial Engineering of W2N/WC Heterostructures Derived from Solid-State Synthesis: A Highly Efficient Trifunctional Electrocatalyst for ORR,OER, and HER

To meet the practical demand of overall water splitting and regenerative metal–air batteries, highly efficient, low-cost, and durable electrocatalysts for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) are required to displace noble metal catalysts. In this work, a facile solid-state synthesis strategy is developed to construct the interfacial engineering of W₂N/WC heterostructures, in which abundant interfaces are formed. Under high temperature (800 °C), volatile CN_x species from dicyanodiamide are trapped by WO₃ nanorods, followed by simultaneous nitridation and carbonization, to form W₂N/WC heterostructure catalysts. The resultant W₂N/WC heterostructure catalysts exhibit an efficient and stable electrocatalytic performance toward the ORR, OER, and HER, including a half-wave potential of 0.81 V (ORR) and a low overpotential at 10 mA cm⁻² for the OER (320 mV) and HER (148.5 mV). Furthermore, a W₂N/WC-based Zn–air battery shows outstanding high power density (172 mW cm⁻²). Density functional theory and X-ray absorption fine structure analysis computations reveal that W₂N/WC interfaces synergistically facilitate transport and separation of charge, thus accelerating the electrochemical ORR, OER, and HER. This work paves a novel avenue for constructing efficient and low-cost electrocatalysts for electrochemical energy devices.     

NiO as a Bifunctional Promoter for RuO2 toward Superior Overall Water Splitting

Conventional development of nanomaterials for efficient electrocatalysis is largely based on performance‐oriented trial‐and‐error/iterative approaches, while a rational design approach at the atomic/molecular level is yet to be found. Here, inspired by a fundamental understanding of the mechanism for both oxygen and hydrogen evolution half reactions (OER/HER), a unique strategy is presented to engineer RuO₂ for superior alkaline water electrolysis through coupling with NiO as an efficient bifunctional promoter. Benefitting from desired potential‐induced interfacial synergies, NiO‐derived NiOOH improves the oxygen binding energy of RuO₂ for enhanced OER, and NiO also promotes water dissociation for enhanced HER on RuO₂‐derived Ru. The resulting hybrid material exhibits remarkable bifunctional activities, affording 2.6 times higher OER activity than that of RuO₂ and an HER activity comparable to Pt/C. As a result, the simple system requires only 1.5 V to deliver 10 mA cm^?2 for overall alkaline water splitting, outperforming the benchmark PtC/NF||IrO₂/NF couple with high mass loading. Comprehensive electrochemical investigation reveals the unique and critical role of NiO on the optimized RuO₂/NiO interface for synergistically enhanced activities, which may be extended to broader (electro)catalytic systems.