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An in situ strategy to simultaneously boost oxygen reduction and oxygen evolution (ORR/OER) activities of commercial carbon textiles is reported and the direct use of such ubiquitous raw material as low‐cost, efficient, robust, self‐supporting, and bifunctional air electrodes in rechargeable Zn‐air batteries is demonstrated. This strategy not only furnishes carbon textiles with a large surface area and hierarchical meso‐microporosity, but also enables efficient dual‐doping of N and S into carbon skeletons while retaining high conductivity and stable monolithic structures. Thus, although original carbon textile has rather poor catalytic activity, the activated textiles without loading other active materials yield effective ORR/OER bifunctionality and stability with a much lower reversible overpotential (0.87 V) than those of Pt/C (1.10 V) and RuO2 (1.02 V) and many reported metal‐free bifunctional catalysts. Importantly, they can concurrently function as current collectors and as ORR/OER catalysts for rechargeable aqueous and flexible solid‐state Zn‐air batteries, showing excellent cell performance, long lifetime, and high flexibility. A judicious in situ activating strategy is developed to concurrently boost the oxygen reduction/evolution activities of commercial carbon textiles without loading any other active materials and eventually transform such ubiquitous raw materials into low‐cost, efficient, robust, self‐standing, additive‐free, and bifunctional air electrodes for direct use in rechargeable liquid and flexible solid‐state Zn‐air batteries.

This work reports a novel approach for the synthesis of FeCo alloy nanoparticles (NPs) embedded in the N,P‐codoped carbon coated nitrogen‐doped carbon nanotubes (NPC/FeCo@NCNTs). Specifically, the synthesis of NCNT is achieved by the calcination of graphene oxide‐coated polystyrene spheres with Fe3+, Co2+ and melamine adsorbed, during which graphene oxide is transformed into carbon nanotubes and simultaneously nitrogen is doped into the graphitic structure. The NPC/FeCo@NCNT is demonstrated to be an efficient and durable bifunctional catalyst for oxygen evolution (OER) and oxygen reduction reaction (ORR). It only needs an overpotential of 339.5 mV to deliver 10 mA cm−2 for OER and an onset potential of 0.92 V to drive ORR. Its bifunctional catalytic activities outperform those of the composite catalyst Pt/C + RuO2 and most bifunctional catalysts reported. The experimental results and density functional theory calculations have demonstrated that the interplay between FeCo NPs and NCNT and the presence of N,P‐codoped carbon structure play important roles in increasing the catalytic activities of the NPC/FeCo@NCNT. More impressively, the NPC/FeCo@NCNT can be used as the air‐electrode catalyst, improving the performance of rechargeable liquid and flexible all‐solid‐state zinc–air batteries. The FeCo alloy nanoparticles embedded in the N,P‐codoped carbon coated nitrogen‐doped carbon nanotubes (NPC/FeCo@NCNT) have been synthesized and demonstrated to be efficient and durable catalysts for oxygen evolution and reduction reactions. It is usable as the air‐electrode catalysts to improve the performance of rechargeable liquid and flexible all‐solid‐state zinc–air batteries.

HighlightsA novel method is developed to prepare bifunctional oxygen electrocatalysts composed of Co nanoparticles and highly dispersed Fe loaded on N-doped carbon substrates by virtues of metal-organic frameworks and two different doping processes.The designed catalysts show comparable performance with commercial catalysts. Meanwhile, rechargeable Zn-air batteries with prepared catalysts demonstrate high peak power density and good cycling stability.The performance promotion originates from the synergy between Co nanoparticles and highly dispersed Fe, porous structures, large specific areas, and distinct three-dimensional carbon networks.  Searching for cheap, efficient, and stable oxygen electrocatalysts is vital to promote the practical performance of Zn-air batteries with high theoretic energy density. Herein, a series of Co nanoparticles and highly dispersed Fe loaded on N-doped porous carbon substrates are prepared through a “double-solvent” method with in situ doped metal-organic frameworks as precursors. The optimized catalysts exhibit excellent performance for oxygen reduction and evolution reaction. Furthermore, rechargeable Zn-air batteries with designed catalysts demonstrate higher peak power density and better cycling stability than those with commercial Pt/C+RuO2. According to structure characterizations and electrochemical tests, the interaction of Co nanoparticles and highly dispersed Fe contributes to the superior performance for oxygen electrocatalysis. In addition, large specific surface areas, porous structures and interconnected three-dimensional carbon networks also play important roles in improving oxygen electrocatalysis. This work provides inspiration for rational design of advanced oxygen electrocatalysts and paves a way for the practical application of rechargeable Zn-air batteries.

HighlightsInterface engineering of heterogeneous CoS/CoO nanocrystals and N-doped graphene composite facilitates high-performance oxygen reduction reaction and oxygen evolution reaction.Density functional theory calculations and experimental results confirm the enhanced electrocatalytic performances via the proposed interface engineering.The bifunctional oxygen electrocatalyst exhibits excellent performances in rechargeable Zn–air batteries.Low cost and green fabrication of high-performance electrocatalysts with earth-abundant resources for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial for the large-scale application of rechargeable Zn–air batteries (ZABs). In this work, our density functional theory calculations on the electrocatalyst suggest that the rational construction of interfacial structure can induce local charge redistribution, improve the electronic conductivity and enhance the catalyst stability. In order to realize such a structure, we spatially immobilize heterogeneous CoS/CoO nanocrystals onto N-doped graphene to synthesize a bifunctional electrocatalyst (CoS/CoO@NGNs). The optimization of the composition, interfacial structure and conductivity of the electrocatalyst is conducted to achieve bifunctional catalytic activity and deliver outstanding efficiency and stability for both ORR and OER. The aqueous ZAB with the as-prepared CoS/CoO@NGNs cathode displays a high maximum power density of 137.8 mW cm−2, a specific capacity of 723.9 mAh g−1 and excellent cycling stability (continuous operating for 100 h) with a high round-trip efficiency. In addition, the assembled quasi-solid-state ZAB also exhibits outstanding mechanical flexibility besides high battery performances, showing great potential for applications in flexible and wearable electronic devices.

Combining morphological control engineering and diatomic coupling strategies, heteronuclear FeCo bimetals are efficiently intercalated into nitrogen‐doped carbon materials with star‐like to simultaneously accelerate oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The half‐wave potential and kinetic current density of the ORR driven by FeCoNC/SL surpass the commercial Pt/C catalyst. The overpotential of OER is as low as 316 mV (η10), and the mass activity is at least 3.2 and 9.4 times that of mononuclear CoNC/SL and FeNC/SL, respectively. The power density and specific capacity of the Zn‐air battery with FeCoNC/SL as air cathode are as high as 224.8 mW cm−2 and 803 mAh g−1, respectively. Morphologically, FeCoNC/SL endows more reactive sites and accelerates the process of oxygen reaction. Density functional theory reveals the active site of the heteronuclear diatomic, and the formation of FeCoN5C configuration can effectively tune the d‐band center and electronic structure. The redistribution of electrons provides conditions for fast electron exchange, and the change of the center of the d‐band avoids the strong adsorption of intermediate species to simultaneously take into account both ORR and OER and thus achieve high‐performance Zn‐air batteries. Morphology‐controlled engineering combined with diatomic coupling strategy to induce heteronuclear FeCo bimetallic with differentiated electron distribution accelerates oxygen reaction for efficient operation of zinc‐air battery energy storage devices.

Engineering of structure and composition is essential but still challenging for electrocatalytic activity modulation. Herein, hybrid nanostructured arrays (HNA) with branched and aligned structures constructed by cobalt selenide (CoSe2) nanotube arrays vertically oriented on carbon cloth with CoNi layered double hydroxide (CoSe2@CoNi LDH HNA) are synthesized by a hydrothermal‐selenization‐hybridization strategy. The branched and hollow structure, as well as the heterointerface between CoSe2 and CoNi LDH guarantee structural stability and sufficient exposure of the surface active sites. More importantly, the strong interaction at the interface can effectively modulate the electronic structure of hybrids through the charge transfer and then improves the reaction kinetics. The resulting branched CoSe2@CoNi LDH HNA as trifunctional catalyst exhibits enhanced electrocatalytic performance toward oxygen evolution/reduction and hydrogen evolution reaction. Consequently, the branched CoSe2@CoNi LDH HNA exhibits low overpotential of 1.58 V at 10 mA cm−2 for water splitting and superior cycling stability (70 h) for rechargeable flexible Zn‐air battery. Theoretical calculations reveal that the construction of heterostructure can effectively lower the reaction barrier as well as improve electrical conductivity, consequently favoring the enhanced electrochemical performance. This work concerning engineering heterostructure and topography‐performance relationship can provide new guidance for the development of multifunctional electrocatalysts. Hierarchical CoSe2@CoNi‐layered double hydroxide (LDH) hybrid nanostructured arrays grown on carbon cloth (CC) are developed as trifunctional catalysts toward oxygen evolution/oxygen reduction/hydrogen evolution reaction. The coupling effect between CoSe2 nanotube and CoNi‐LDH nanosheets as well as the branched nanostructure enable CoSe2@CoNi‐LDH/CC hybrid nanostructured arrays with faster dynamics and more active sites, leading to satisfactory performance toward water splitting and Zn‐air batteries.

HighlightsA novel heterostructured bimetallic Co/CoFe nanomaterial supported on nanoflower-like N-doped graphitic carbon (NC) is prepared through a strategy of coordination construction-cation exchange-pyrolysis.The Co/CoFe@NC exhibits high bifunctional activities with a remarkably small potential gap of 0.70 V between oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), which can be used in liquid and flexible quasi-solid-state rechargeable Zn–air batteries.The density functional theory calculations reveal optimized adsorption energies for intermediates of ORR and OER on heterostructured Co/CoFe@NC.Metal–air batteries, like Zn–air batteries (ZABs) are usually suffered from low energy conversion efficiency and poor cyclability caused by the sluggish OER and ORR at the air cathode. Herein, a novel bimetallic Co/CoFe nanomaterial supported on nanoflower-like N-doped graphitic carbon (NC) was prepared through a strategy of coordination construction–cation exchange-pyrolysis and used as a highly efficient bifunctional oxygen electrocatalyst. Experimental characterizations and density functional theory calculations reveal the formation of Co/CoFe heterostructure and synergistic effect between metal layer and NC support, leading to improved electric conductivity, accelerated reaction kinetics, and optimized adsorption energy for intermediates of ORR and OER. The Co/CoFe@NC exhibits high bifunctional activities with a remarkably small potential gap of 0.70 V between the half-wave potential (E1/2) of ORR and the potential at 10 mA cm‒2 (Ej=10) of OER. The aqueous ZAB constructed using this air electrode exhibits a slight voltage loss of only 60 mV after 550-cycle test (360 h, 15 days). A sodium polyacrylate (PANa)-based hydrogel electrolyte was synthesized with strong water-retention capability and high ionic conductivity. The quasi-solid-state ZAB by integrating the Co/CoFe@NC air electrode and PANa hydrogel electrolyte demonstrates excellent mechanical stability and cyclability under different bending states.

HighlightsOxygen-respirable sponge was constructed by carbon dots-assisted synthesis strategy.The hydrophilicity and aerophilicity of Co@C–O–Cs active sites boost oxygen diffusion and the bifunctional oxygen reduction reaction and oxygen evolution reaction activities.Co@C–O–Cs-based Zn-air battery (ZAB) displays excellent specific capacity and stability, and the all-solid-state Co@C–O–Cs-based ZAB exhibits excellent flexibility.Efficient bifunctional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are vital for rechargeable Zn-air batteries (ZABs). Herein, an oxygen-respirable sponge-like Co@C–O–Cs catalyst with oxygen-rich active sites was designed and constructed for both ORR and OER by a facile carbon dot-assisted strategy. The aerophilic triphase interface of Co@C–O–Cs cathode efficiently boosts oxygen diffusion and transfer. The theoretical calculations and experimental studies revealed that the Co–C–COC active sites can redistribute the local charge density and lower the reaction energy barrier. The Co@C–O–Cs catalyst displays superior bifunctional catalytic activities with a half-wave potential of 0.82 V for ORR and an ultralow overpotential of 294 mV at 10 mA cm−2 for OER. Moreover, it can drive the liquid ZABs with high peak power density (106.4 mW cm−2), specific capacity (720.7 mAh g−1), outstanding long-term cycle stability (over 750 cycles at 10 mA cm−2), and exhibits excellent feasibility in flexible all-solid-state ZABs. These findings provide new insights into the rational design of efficient bifunctional oxygen catalysts in rechargeable metal-air batteries.

The development of simple and effective strategies to prepare electrocatalysts, which possess unique and stable structures comprised of metal/nonmetallic atoms for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), is currently an urgent issue. Herein, an efficient bifunctional electrocatalyst featured by ultralong N, S‐doped carbon nano‐hollow‐sphere chains about 1300 nm with encapsulated Co nanoparticles (Co‐CNHSCs) is developed. The multifunctional catalytic properties of Co together with the heteroatom‐induced charge redistribution (i.e., modulating the electronic structure of the active site) result in superior catalytic activities toward OER and ORR in alkaline media. The optimized catalyst Co‐CNHSC‐3 displays an outstanding electrocatalytic ability for ORR and OER, a high specific capacity of 1023.6 mAh gZn−1, and excellent reversibility after 80 h at 10 mA cm−2 in a Zn‐air battery system. This work presents a new strategy for the design and synthesis of efficient multifunctional carbon‐based catalysts for energy storage and conversion devices. An ultralong N,S co‐doped carbon nano‐hollow‐sphere chain with encapsulated Co nanoparticles (Co‐CNHSC) is synthesized as a bifunctional catalyst for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) by adopting a one‐step pyrolysis method. Benefiting from the electronic structure modulation between metal and nonmetal species, the optimized Co‐CNHSC‐3 exhibits an excellent bifunctional activity for OER and ORR and also shows superior performance for Zn‐air batteries.

Developing cost‐efficient trifunctional catalysts capable of facilitating hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) activity is essential for the progression of energy devices. Engineering these catalysts to optimize their active sites and integrate them into a cohesive system presents a significant challenge. This study introduces a nanoflower (NFs)‐like carbon‐encapsulated FeNiPt nanoalloy catalyst (FeNiPt@C NFs), synthesized by substituting Co2+ ions with high‐spin Fe2+ ions in Hofmann‐type metal‐organic framework, followed by carbonization and pickling processes. The FeNiPt@C NFs catalyst, characterized by its nitrogen‐doped carbon‐encapsulated metal alloy structure and phase‐segregated FeNiPt alloy with slight surface oxidization, exhibits excellent trifunctional catalytic performance. This is evidenced by its activities in HER (−25 mV at 10 mA cm−2), ORR (half‐wave potential of 0.93 V), and OER (294 mV at 10 mA cm−2), with the enhanced water oxidation activity attributed to the high‐spin state of the Fe element. Consequently, the Zn‐air battery and anion exchange membrane water electrolyzer assembled by FeNiPt@C NFs catalyst demonstrate remarkable power density (168 mW cm−2) and industrial‐scale current density (698 mA cm−2 at 1.85 V), respectively. This innovative integration of multifunctional catalytic sites paves the way for the advancement of sustainable energy systems. The nanoflower‐like carbon‐encapsulated FeNiPt nanoalloy hierarchical structure (FeNiPt@C NFs catalyst) is successfully synthesized by pyrolyzing metal‐organic framework, exhibiting exceptional performance in HER/OER/ORR. Notably, spin‐induced enhanced water oxidation is observed for the first time in a carbon‐encapsulated alloy catalyst. Therefore, a trifunctional FeNiPt@C NFs catalyst is developed as an exemplary model for designing and synthesizing efficient and stable multifunctional catalysts.