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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.

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.

The increasingly serious environmental challenges have gradually aroused people’s interest in electric vehicles. Over the last decade, governments and automakers have collaborated on the manufacturing of electric vehicles with high performance. Cutting-edge battery technologies are pivotal for the performance of electric vehicles. Zn–air batteries are considered as potential power batteries for electric vehicles due to their high capacity. Zn–air battery researches can be classified into three categories: primary batteries, mechanically rechargeable batteries, and chemically rechargeable batteries. The majority of current studies aim at developing and improving chemically rechargeable and mechanically rechargeable Zn–air batteries. Researchers have tried to use catalytic materials design and device design for Zn–air batteries to make it possible for their applications in electric vehicles. This review will highlight the state-of-the-art in primary batteries, mechanically rechargeable batteries, and chemically rechargeable batteries, revealing the prospects of Zn–air batteries for electric vehicles.

Transition metal and metal oxide heterojunctions have been widely studied as bifunctional oxygen reduction/evolution reaction (ORR/OER) electrocatalysts for Zn‐air batteries, but the dynamic changes of transition metal oxides and the interface during catalysis are still unclear. Here, bifunctional electrocatalyst of Co─Co2Nb5O14 is reported, containing lattice interlocked Co nanodots and Co2Nb5O14 nanorods, which construct a strong metal‐support interaction (SMSI) interface. Unlike the recognition that transition metals mainly serve as ORR active sites and metal oxides as OER active sites, it is found that both ORR/OER sites originate from Co2Nb5O14, while Co acts as an electronic regulatory unit. The SMSI interface promotes dynamic electron transfer between Co/Co2Nb5O14, and the reversible active sites of Nb4+/Nb5+ realize bidirectional adsorption/migration of intermediates, thereby achieving dynamic reversible interface reconstitution. The electrocatalyst shows a high ORR half‐wave potential of 0.84 V, a low OER overpotential of 296.3 mV, and great cycling stability over 30000 s. The ZAB shows a high capacity of 850.6 mA h·gZn−1 and can stably run 2050 cycles at 10 mA·cm⁻2. Moreover, the constructed solid‐state ZAB also shows leading cycling stability in comparison with the previous studies. A bifunctional electrocatalyst of Co─Co2Nb5O14 with a strong interaction interface is fabricated, and a bidirectional adsorption/migration mechanism of oxygen species between the reversible active sites of Nb5+/Nb4+ has been proposed. With the catalytic strategy design, the liquid Zn‐air batteries exhibits long‐term stability over 2050 cycles, and the solid‐state Zn‐air batteries also exhibits leading long‐cycling stability.

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.

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.

Designing bifunctional oxygen electrocatalysts with high activity, lasting stability, and low-cost for rechargeable zinc-air batteries (RZABs) is a tough challenge. Herein, an advanced electrocatalyst is prepared by anchoring atomically dispersed Co atoms on N-doped graphene-like hierarchically porous carbon nanosheets (SA-Co-N 4 -GCs) and thereby forming Co-N 4 -C architecture. Its unique structure with excellent conductivity, large surface area, and three dimensional (3D) interconnected hierarchically porous architecture exposes not only more Co-N 4 active sites to accelerate the kinetics of both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), but also provides an efficient charge/mass transport environment to reduce diffusion barrier. Consequently, SA-Co-N 4 -GCs exhibits excellent ORR/OER bifunctional activities and durability, surpassing noble-metal catalysts. Liquid RZABs using SA-Co-N 4 -GCs cathodes display a high open-circuit voltage of 1.51 V, a remarkable power density of 149.3 mW·cm −2 , as well as excellent stability and rechargeability with faint increase in polarization even at a large depth of charge—discharge cycle with 16 h per cycle over an entire 600 h long-term test. Moreover, flexible quasi-solid-state RZABs with SA-Co-N 4 -GCs cathodes also deliver a considerable power density of 124.5 mW·cm −2 , which is even higher than that of liquid batteries using noble-metal catalysts. This work has thrown new insight into development of high-performance and low-cost electrocatalysts for energy conversion and storage.

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.

NiFe layered double hydroxide (NiFe-LDH) nanosheets and metal-nitrogen-carbon materials (M-N-C, M = Ni, Fe, Co, etc.) are supreme catalysts in the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) process, respectively. Nevertheless, the monotonic performance and insufficient stability severely hamper their practical application in rechargeable batteries. Herein, we simultaneously combine ultrathin NiFe-LDH nanowalls with renewable soybean-derived Fe-N-C matrix to obtain a hybrid materials (NiFe-LDH/FeSoy-CNSs-A), which exhibits robust catalytic activities for OER ( E j=10 = 1.53 V vs. RHE) and ORR ( E 1/2 = 0.91 V vs. RHE), with a top-notch battery parameters and stability in assembled rechargeable Zn-air batteries. Intensive investigations indicate that the vertically dispersed NiFe-LDH nanosheets, Fe-N-C matrix derived from soybean and the strong synergy between them are responsible for the unprecedented OER and ORR performances. The key role of intrinsic N defects involved in the hybrid materials is firstly specified by ultrasoundassisted extraction of soy protein from soybean. The exquisite design can facilitate the utilization of sustainable biomass-derived catalysts, and the mechanism investigations of N defects and oxygenic groups on the structure-activity relationship can stimulate the progress of other functional hybrid electrocatalysts.

In this study, Co/Ni‐NC catalyst with hetero‐diatomic Co/Ni active sites dispersed on nitrogen‐doped carbon matrix is synthesized via the controlled pyrolysis of ZIF‐8 containing Co2+ and Ni2+ compounds. Experimental characterizations and theoretical calculations reveal that Co and Ni are atomically and uniformly dispersed in pairs of CoN4‐NiN4 with an intersite distance ≈0.41 nm, and there is long‐range d–d coupling between Co and Ni with more electron delocalization for higher bifunctional activity. Besides, the in situ grown carbon nanotubes at the edges of the catalyst particles allow high electronic conductivity for electrocatalysis process. Electrochemical evaluations demonstrate the superior ORR and OER bifunctionality of Co/Ni‐NC catalyst with a narrow potential gap of only 0.691 V and long‐term durability, significantly prevailing over the single‐atom Co‐NC and Ni‐NC catalysts and the benchmark Pt/C and RuO2 catalysts. Co/Ni‐NC catalyzed Zn–air batteries achieve a high specific capacity of 771 mAh g−1 and a long continuous operation period up to 340 h with a small voltage gap of ≈0.65 V, also much superior to Pt/C‐RuO2. CoN4‐NiN4 site pairs with long‐range coupling are atomically dispersed on nitrogen‐doped carbon matrix, and the resultant catalyst is found to show excellent ORR/OER bi‐functionality and used as cathode catalyst for high‐performance rechargeable Zn–air battery.