In Situ Coupling Strategy for Anchoring Monodisperse Co_9S_8 Nanoparticles on S and N Dual?Doped Graphene as a Bifunctional Electrocatalyst for Rechargeable Zn–Air Battery

An in situ coupling strategy to prepare Co_9S_8/S and N dual?doped graphene composite(Co_9S_8/NSG) has been proposed. The key point of this strategy is the function?oriented design of organic compounds. Herein, cobalt porphyrin derivatives with sulfo groups are employed as not only the coupling agents to form and anchor Co_9S_8 on the graphene in situ, but also the heteroatom?doped agent to generate S and N dual?doped graphene. The tight coupling of multiple active sites endows the composite materials with fast electrochemical kinetics and excellent stability for both oxygen reduction reaction(ORR) and oxygen evolution reaction(OER). The obtained electrocatalyst exhibits better activity parameter(ΔE = 0.82 V) and smaller Tafel slope(47.7 mV dec^(-1) for ORR and 69.2 mV dec^(-1) for OER) than commercially available Pt/C and RuO_2. Most importantly, as electrocatalyst for rechargeable Zn–air battery, Co_9S_8/NSG displays low charge–discharge voltage gap and outstanding long?term cycle stability over 138 h compared to Pt/C–RuO_2. To further broaden its application scope, a homemade all?solid?state Zn–air battery is also prepared, which displays good charge–discharge performance and cycle performance. The function?oriented design of N_4?metallomacrocycle derivatives might open new avenues to strategic construction of high?performance and long?life multifunctional electrocatalysts for wider electro?chemical energy applications.

Ni–Co bimetallic coordination effect for long lifetime rechargeable Zn–air battery

The development of bifunctional oxygen electrocatalysts with high efficiency, high stability, and low cost is of great significance to the industrialization of rechargeable Zn–air batteries. A widely accepted view is that the oxygen reduction reaction(ORR) and the oxygen evolution reaction(OER) follow different catalytic mechanisms, and accordingly they need different active sites for catalysis. Transition metal elements have admirable electronic acceptance ability for coordinating with reactants, and this can weaken the bond energy between reactants, thus promoting the ORR or OER reactions. Herein, the ORR and OER activities of different transition metal supported nitrogen-doped carbon nanotubes were systematically studied and compared. The optimal catalyst for synchronous ORR and OER was obtained by pyrolyzing melamine, cobalt nitrate, and nickel nitrate on carbon nanotubes, called cobalt–nickel supported nitrogenmixed carbon nanotubes(CoNi–NCNT), which were equipped with two types of high-performance active sites—the Co/Ni–N–C structure for the ORR and Co Ni alloy particles for the OER—simultaneously. Remarkably, the optimized Co Ni–NCNT exhibited a satisfactory bifunctional catalytic activity for both the ORR and OER. The value of the oxygen electrode activity parameter,△E, of CoNi–NCNT was 0.81 V, which surpasses that of catalysts Pt/C and Ir/C, and most of the non-precious metal-based bifunctional electrocatalysts reported in previous literatures. Furthermore, a specially assembled rechargeable Zn–air cell with Co Ni–NCNT loaded carbon paper as an air cathode was used to evaluate the practicability. As a result, a superior specific capacity of 744.3 mAh/gZn, a peak power density of 88 mW/cm2, and an excellent rechargeable cycling stability were observed, and these endow the Co Ni–NCNT with promising prospects for practical application.

Electrolyte additive enhances the electrochemical performance of Cu for rechargeable Cu//Zn batteries

Cu-based cathodes in aqueous batteries become very attractive in view of high theoretical capacity,moderate operation voltage and rich reserves of raw materials.However,their applications are obstructed by serious side reactions.The side reaction mainly arises from the spontaneous formation of Cu_(2)O,which occupies the electrode surface and lowers the reaction reversibility.Here,Na_(2)EDTA is introduced to address these issues.Both experimental results and theoretical calculations indicate that the Na_(2)EDTA reshapes the solvation structure of Cu^(2+)and modifies the electrode/electrolyte interface.Therefore,the redox potential of Cu^(2+)/Cu_(2)O is reduced and the surface of Cu is protected from H2O,thereby inhibiting the formation of Cu_(2)O.Meanwhile,the change in the solvation structure reduces the electrostatic repulsion between Cu^(2+)and the cathode,leading to high local concentration and benefiting uniform deposition.The results shed light on the applications of rechargeable Cu-based batteries.

Bifunctional Oxygen Electrocatalyst of Mesoporous Ni/NiO Nanosheets for Flexible Rechargeable Zn–Air Batteries

One approach to accelerate the stagnant kinetics of both the oxygen reduction and evolution reactions(ORR/OER)is to develop a rationally designed multiphase nanocomposite,where the functions arising from each of the constituent phases,their interfaces,and the overall structure are properly controlled.Herein,we successfully synthesized an oxygen electrocatalyst consisting of Ni nanoparticles purposely interpenetrated into mesoporous NiO nanosheets(porous Ni/NiO).Benefiting from the contributions of the Ni and NiO phases,the well-established pore channels for charge transport at the interface between the phases,and the enhanced conductivity due to oxygen-deficiency at the pore edges,the porous Ni/NiO nanosheets show a potential of 1.49 V(10 mA cm^-2)for the OER and a half-wave potential of 0.76 V for the ORR,outperforming their noble metal counterparts.More significantly,a Zn-air battery employing the porous Ni/NiO nanosheets exhibits an initial charging-discharging voltage gap of 0.83 V(2 mA cm^-2),specific capacity of 853 mAh gZn^-1 at 20 mA cm^-2,and long-time cycling stability(120 h).In addition,the porous Ni/NiO-based solid-like Zn-air battery shows excellent electrochemical performance and flexibility,illustrating its great potential as a next-generation rechargeable power source for flexible electronics.

Engineering core–shell Co_(9)S_(8)/Co nanoparticles on reduced graphene oxide: Efficient bifunctional Mott–Schottky electrocatalysts in neutral rechargeable Zn–Air batteries

It is significant for the rational construction of the high–efficient bifunctional electrocatalysts for in–depth understandings of how to improve the electron transfer and ion/oxygen transport in catalyzing oxygen reduction reaction and oxygen evolution reaction(ORR and OER),but still full of vital challenges.Herein,we synthesize the novel“three–in–one”catalyst that engineers core–shell Mott–Schottky Co_(9)S_(8)/Co heterostructure on the defective reduced graphene oxide(Co_(9)S_(8)/Co–rGO).The Co_(9)S_(8)/Co–rGO catalyst exhibits abundant Mott–Schottky heterogeneous–interfaces,the well–defined core–shell nanostructure as well as the defective carbon architecture,which provide the multiple guarantees for enhancing the electron transfer and ion/oxygen transport,thus boosting the catalytic ORR and OER activities in neutral electrolyte.As expected,the integrated core–shell Mott–Schottky Co_(9)S_(8)/Co–rGO catalyst delivers the most robust and efficient rechargeable ZABs performance in neutral solution electrolytes accompanied with a power density of 59.5 mW cm^(-2) and superior cycling stability at 5 mA cm^(-2) over 200 h.This work not only emphasizes the rational designing of the high–efficient bifunctional oxygen catalysts from the fundamental understanding of accelerating the electron transfer and ion/oxygen transport,but also sheds light on the practical application prospects in more friendly environmentally neutral rechargeable ZABs.

Core-shell-structured Co@Co4N nanoparticles encapsulated into MnO-modified porous N-doping carbon nanocubes as bifunctional catalysts for rechargeable Zn–air batteries

Designing the highly catalytic activity and durable bifunctional catalysts toward oxygen reduction/evolution reaction(ORR/OER) is paramount for metal–air batteries. Metal–organic frameworks(MOFs)-based materials have attracted a great deal of attention as the potential candidate for effectively catalyzing ORR/OER due to their adjustable composition and porous structure. Herein, we first introduce the Mn species into zeolitic-imidazole frameworks(ZIFs) and then further pyrolyze the Mn-containing bimetallic ZIFs to synthesize core-shell-structured Co@Co4N nanoparticles embedded into MnO-modified porous N-doped carbon nanocubes(Co@Co4N/MnO–NC). Co@Co4N/MnO–NC exhibits the outstanding catalytic activity toward ORR and OER which is attributed to its abundant pyridinic/graphitic N and Co4N,the optimized content of MnO species, highly dispersed catalytic sites and porous carbon matrix. As a result, the Co@Co4N/MnO–NC-based Zn–air battery exhibits enhanced performances, including the high discharge capacity(762 mA h gZn-1), large power density(200.5 mW cm-2), stable potential profile over 72 h, low overpotential(<1.0 V) and superior cycling life(2800 cycles). Moreover, the belt-shaped Co@Co4N/MnO–NC cathode-based Zn–air batteries are also designed which exhibit the superb electrochemical properties at different bending/twisting conditions.

Hierarchical sulfur and nitrogen co-doped carbon nanocages as efficient bifunctional oxygen electrocatalysts for rechargeable Zn-air battery

Exploring inexpensive and efficient bifunctional electrocatalysts for oxygen reduction reaction(ORR) and oxygen evolution reaction(OER) is critical for rechargeable metal-air batteries. Herein, we report a new 3D hierarchical sulfur and nitrogen co-doped carbon nanocages(hSNCNC) as a promising bifunctional oxygen electrocatalyst by an in-situ MgO template method with pyridine and thiophene as the mixed precursor. The as-prepared h SNCNC exhibits a positive half-wave potential of 0.792 V(vs. reversible hydrogen electrode, RHE) for ORR, and a low operating potential of 1.640 V at a 10 mA cm-2 current density for OER. The reversible oxygen electrode index is 0.847 V, far superior to commercial Pt/C and IrO2,which reaches the top level of the reported bifunctional catalysts. Consequently, the hSNCNC as air cathodes in an assembled Zn-air battery features low charge/discharge overpotential and long lifetime. The remarkable properties arises from the introduced multiple heteroatom dopants and stable 3D hierarchical structure with multi-scale pores, which provides the abundant uniform high-active S and N species and efficient charge transfer as well as mass transportation. These results demonstrate the potential strategy in developing suitable carbon-based bi-/multi-functional catalysts to enable the next generation of the rechargeable metal-air batteries.

Graphitic‐shell encapsulated FeNi alloy/nitride nanocrystals on biomass‐derived N‐doped carbon as an efficient electrocatalyst for rechargeable Zn‐air battery

Oxygen reduction/evolution reactions(ORR/OERs)catalysts play a key role in the metal‐air battery and water‐splitting process.Herein,we developed a facile template‐free method to fabricate a new type of non–noble metal‐based hybrid catalyst which consists of binary FeNi alloy/nitride nanocrystals with graphitic‐shell and biomass‐derived N‐doped carbon(NC)(FexNiyN@C/NC).This novel nanostructure exhibits superior performance for ORR/OER,which can be attributed to the strong interactions between the graphitic‐shell encapsulated FeNi alloy/nitride nanocrystals and the N‐doped porous carbon substrate.The X‐ray absorption spectroscopy technique was employed to reveal the underlying mechanisms for the excellent performance.The assembled Zn‐air battery device exhibits outstanding charging/discharging performance and cycling stability,indicating the great potential of this type of novel catalysts.

Rechargeable Zn-air batteries initiated by nickel–cobalt bimetallic selenide

A Zn-air battery is a potential next-generation energy storage device owing to its extremely high theoretical energy density. Currently, it is important to explore non-precious metal electrocatalysts with high electroactivity and stability in the oxygen reduction reaction(ORR) and oxygen evolution reaction(OER) for the development of Zn-air batteries. In this work, porous(Ni,Co)Se2 nanosheets were synthesized by selenizing Ni Co2O4 nanosheets. By regulating the conductivity and morphology of the sample, the prepared porous(Ni,Co)Se2 nanosheets show enhanced electrocatalytic activity for OER and ORR compared to Ni Co2O4 nanosheets. The aqueous Zn-air battery using porous(Ni,Co)Se2 nanosheets as the air cathode exhibits superior charge and discharge performance(1.98 V for charging and 1.17 V for discharging), high specific capacity(770 m Ah/g), and excellent cycle stability(140 h). These results indicate that the porous(Ni,Co)Se2 nanosheets are suitable as a bifunctional electrocatalyst for future Zn-air batteries.

Co/Ni dual-metal embedded in heteroatom doped porous carbon core-shell bifunctional electrocatalyst for rechargeable Zn-air batteries

Rational construction of highly efficient and cheap bifunctional electrocatalysts to boost both oxygen evolution reaction(OER)and oxygen reduction reaction(ORR)is extremely essential for the wide application of rechargeable metal-air battery.In this work,we design a core-shell structural catalyst of CoNi dual-metal embedded in nitrogen doped porous carbon(NPC,CoNi@NPC),which is developed via the pyrolysis of CoNiMOFs,assisting by mesoporous SiO_(2) to effectively inhibit the aggregation of metal sites.Consequently,the asprepared CoNi@NPC manifests good ORR activity with half-wave potential up to 0.77 V.Specifically,the CoNi@NPC gives a very low OER over-potential of merely 101 mV in 6 M KOH along with high stability,outperforming the commercial Pt/C-RuO_(2).Moreover,the home-made zinc air battery with CoNi@NPC air cathode demonstrates excellent stability over long-term charging–discharging test,and delivers the maximum power density of 224 mW cm^(-2).The enhanced high performance of CoNi@NPC bifunctional catalyst for both ORR and OER can be ascribed to its unique core-shell structure and strong synergistic effect between the dual-bimetal active sites and the heteroatom doped carbon.This work opens a new avenue for the rational design of nonprecious metal bifunctional catalysts for rechargeable metal-air battery.

Flexible rechargeable Ni//Zn battery based on self-supported NiCo_2O_4 nanosheets with high power density and good cycling stability

The overall electrochemical performances of Ni-Zn batteries are still far from satisfactory, specifically for rate performance and cycling stability Herein, we demonstrated a high-performance flexible Ni//Zn battery with outstanding durability and high power density based on selfsupported NiCo_2 O_4 nanosheets as cathode and Zn nanosheets as anode. This Ni//Zn battery is able to deliver a remarkable capacity of183.1 mAh g^(-1) and a good cycling performance(82.7% capacity retention after 3500 cycles). More importantly, this battery achieves an admirable power density of 49.0 kW kg^(-1) and energy density of 303.8 Wh kg^(-1), substantially higher than most recently reported batteries. With such excellent electrochemical performance, this battery will have great potential as an ultrafast power source in practical application.

Carbon-based cathode materials for rechargeable zinc-air batteries: From current collectors to bifunctional integrated air electrodes

Rechargeable zinc-air batteries(ZABs)have attracted much attention as the next-generation energy conversion and storage devices due to the abundance and environmental friendliness of zinc(Zn)for anode materials,as well as the safety and low cost of aqueous electrolytes.However,rational design of nonprecious and low-cost integrated air cathode materials with a desirable bifunctional oxygen electrocatalytic performance remains a great challenge for the commercialization of rechargeable ZABs.In previous research studies,various cost-effective carbon-supported electrocatalysts and light-weight carbon-based current collectors for air cathodes have been developed,showing vast potential in the application of carbon-based materials.To improve the bifunctional performance and integration of air cathodes,efforts with respect to the design of morphology,defects,and synergistic effects of carbon-based materials have been made.In this perspective,the general understanding of the air cathode construction and the battery working mechanism is discussed.The recent progress in the design of carbon-based materials for air cathodes in rechargeable ZABs is summarized.Several possible future research directions and the expected development trends are also discussed,aiming to facilitate the commercialization of advanced rechargeable ZABs in our life.

3D hollow sphere Co_3O_4/MnO_2-CNTs:Its high-performance bi-functional cathode catalysis and application in rechargeable zinc-air battery

There has been a continuous need for high active, excellently durable and low-cost electrocatalysts for rechargeable zinc-air batteries. Among many low-cost metal based candidates, transition metal oxides with the CNTs composite have gained increasing attention. In this paper, the 3-D hollow sphere MnO_2 nanotube-supported Co_3O_4 nanoparticles and its carbon nanotubes hybrid material(Co_3 O_4/MnO_2-CNTs) have been synthesized via a simple co-precipitation method combined with post-heat treatment. The morphology and composition of the catalysts are thoroughly analyzed through SEM, TEM, TEM-mapping, XRD, EDX and XPS. In comparison with the commercial 20% Pt/C, Co_3O_4/MnO_2,bare MnO_2 nanotubes and CNTs, the hybrid Co_3O_4/MnO_2-CNTs-350 exhibits perfect bi-functional catalytic activity toward oxygen reduction reaction and oxygen evolution reaction under alkaline condition(0.1 M KOH). Therefore, high cell performances are achieved which result in an appropriate open circuit voltage(～1.47 V),a high discharge peak power density(340 mW cm^(-2)) and a large specific capacity(775 mAh g^(-1) at 10 mA cm^(-2)) for the primary Zn-air battery, a small charge-discharge voltage gap and a high cycle-life(504 cycles at 10 mA cm^(-2) with 10 min per cycle) for the rechargeable Zn-air battery. In particular, the simple synthesis method is suitable for a large-scale production of this bifunctional material due to a green, cost effective and readily available process.

Vacancies and interfaces engineering of core-shell heterostuctured NiCoP/NiO as trifunctional electrocatalysts for overall water splitting and zinc-air batteries

The electronic structures and properties of electrocatalysts,which depend on the physicochemical structure and metallic element components,could significantly affect their electrocatalytic performance and their future applications in Zn-air battery(ZAB)and overall water splitting(OWS).Here,by combining vacancies and heterogeneous interfacial engineering,three-dimensional(3D)core-shell NiCoP/NiO heterostructures with dominated oxygen vacancies have been controllably in-situ grown on carbon cloth for using as highly efficient electrocatalysts toward hydrogen and oxygen electrochemical reactions.Theoretical calculation and electrochemical results manifest that the hybridization of NiCoP core with NiO shell produces a strong synergistic electronic coupling effect.The oxygen vacancy can enable the emergence of new electronic states within the band gap,crossing the Fermi levels of the two spin components and optimizing the local electronic structure.Besides,the hierarchical core-shell NiCoP/NiO nanoarrays also endow the catalysts with multiple exposed active sites,faster mass transfer behavior,optimized electronic strutures and improved electrochemical performance during ZAB and OWS applications.

Flexible, Porous, and Metal–Heteroatom?Doped Carbon Nanofibers as Efficient ORR Electrocatalysts for Zn–Air Battery

Developing an e cient and durable oxygen reduction electrocatalyst is critical for clean-energy technology, such as fuel cells and metal–air batteries. In this study, we developed a facile strategy for the preparation of flexible, porous, and well-dispersed metal–heteroatom-doped carbon nanofibers by direct carbonization of electrospun Zn/Co-ZIFs/PAN nanofibers(Zn/Co-ZIFs/PAN). The obtained Zn/Co and N co-doped porous carbon nanofibers carbonized at 800 °C(Zn/Co–N@PCNFs-800) presented a good flexibility, a continuous porous structure, and a superior oxygen reduction reaction(ORR) catalytic activity to that of commercial 20 wt% Pt/C, in terms of its onset potential(0.98 V vs. RHE), half-wave potential(0.89 V vs. RHE), and limiting current density(-5.26 mA cm^(-2)). In addition, we tested the suitability and durability of Zn/Co–N@PCNFs-800 as the oxygen cathode for a rechargeable Zn–air battery. The prepared Zn–air batteries exhibited a higher power density(83.5 mW cm^(-2)), a higher specific capacity(640.3 mAh g^(-1)), an excellent reversibility, and a better cycling life than the commercial 20 wt% Pt/C + RuO_2 catalysts. This design strategy of flexible porous non-precious metal-doped ORR electrocatalysts obtained from electrospun ZIFs/polymer nanofibers could be extended to fabricate other novel, stable, and easy-to-use multi-functional electrocatalysts for clean-energy technology.

Bimetallic Nickel Cobalt Sulfide as E cient Electrocatalyst for Zn–Air Battery and Water Splitting

The development of e cient earth-abundant electrocatalysts for oxygen reduction, oxygen evolution, and hydrogen evolution reactions(ORR, OER, and HER) is important for future energy conversion and energy storage devices, for which both rechargeable Zn–air batteries and water splitting have raised great expectations. Herein, we report a single-phase bimetallic nickel cobalt sulfide((Ni,Co)S_2) as an e cient electrocatalyst for both OER and ORR. Owing to the synergistic combination of Ni and Co, the(Ni,Co)S_2 exhibits superior electrocatalytic performance for ORR, OER, and HER in an alkaline electrolyte, and the first principle calculation results indicate that the reaction of an adsorbed O atom with a H_2O molecule to form a *OOH is the potential limiting step in the OER. Importantly, it could be utilized as an advanced air electrode material in Zn–air batteries, which shows an enhanced charge–discharge performance(charging voltage of 1.71 V and discharge voltage of 1.26 V at 2 mA cm^(-2)), large specific capacity(842 mAh g_(Zn)^(-1) at 5 mA cm^(-2)), and excellent cycling stability(480 h). Interestingly, the(Ni,Co)S_2-based Zn–air battery can e ciently power an electrochemical water-splitting unit with(Ni,Co)S_2 serving as both the electrodes. This reveals that the prepared(Ni,Co)S_2 has promising applications in future energy conversion and energy storage devices.

Hollow cobalt oxide nanoparticles embedded in nitrogen-doped carbon nanosheets as an efficient bifunctional catalyst for Zn–air battery

Rational design of low-cost, highly electrocatalytic activity, and stable bifunctional electrocatalysts for oxygen reduction reaction(ORR) and oxygen evolution reaction(OER) has been a great significant for metal–air batteries. Herein, an efficient bifunctional electrocatalyst based on hollow cobalt oxide nanoparticles embedded in nitrogen-doped carbon nanosheets(Co/N-Pg) is fabricated for Zn–air batteries. A lowcost biomass peach gum, consisting of carbon, oxygen, and hydrogen without other heteroatoms, was used as carbon source to form carbon matrix hosting hollow cobalt oxide nanoparticles. Meanwhile, the melamine was applied as nitrogen source and template precursor, which can convert to carbon-based template graphitic carbon nitride by polycondensation process. Owing to the unique structure and synergistic effect between hollow cobalt oxide nanoparticles and Co-N-C species, the proposal Co/N-Pg catalyst displays not only prominent bifunctional electrocatalytic activities for ORR and OER, but also excellent durability. Remarkably, the assembled Zn–air battery with Co/N-Pg air electrode exhibited a low discharge-charge voltage gap(0.81 V at 50 mA cm^-2) and high peak power density(119 mW cm^-2) with long-term cycling stability. This work presents an effective approach for engineering transition metal oxides and nitrogen modified carbon nanosheets to boost the performance of bifunctional electrocatalysts for Zn–air battery.

In-situ emb e dding zeolitic imidazolate framework derived Co–N–C bifunctional catalysts in carbon nanotube networks for flexible Zn–air batteries

Recently, the development of high-performance bifunctional oxygen catalysts integrated with flexible conductive scaffolds f or rechargeable metal-air batteries has attracted considerable interest, driving by fastgrowing wearable electronics. Herein, we report a flexible bifunctional oxygen catalyst thin film consisting of Co–N–C bifunctional catalysts embedding in carbon nanotube(CNT) networks. The catalyst is readily prepared by pyrolysis of cobalt-based zeolitic imidazolate frameworks(ZIF-67) that are in-situ synthesized in CNT networks. Such catalyst film demonstrates very high catalytic activities for oxygen reduction(onset potential: 0.91 V, and half-wave potential: 0.87 V vs. RHE) and oxygen evolution(10 m Acm^-2 at 1.58 V) reactions, high methanol tolerance property, and long-term stability(97% current retention). Moreover, our integrated catalyst film shows very good structure flexibility and robustness. Based on the obtained film air electrodes, flexible Zn–air batteries demonstrate low charging and discharging overpotentials(0.82 V at 1 m A cm^-1) and excellent structure stability in the bending tests. These results indicate that presently reported catalyst films are potential air electrodes for flexible metal–air batteries.

Construction of surface lattice oxygen in metallic N-CuCoS1.97 porous nanowire for wearable Zn-air battery

Achieving high activity and stability oxygen evolution reaction(OER) catalysts to optimize the efficiency of metal-air battery, water splitting and other energy conversion devices, remains a formidable challenge.Herein, we demonstrate the metallic porous nanowires arrays with abundant defects via nitrogen and copper codoped CoS1.97 nanowires(N-CuCoS1.97 NWs). The N-CuCoS1.97 NWs can serve as an excellent OER self-supported electrode with an overpotential of 280 mV(j = 10 m A cm-2) and remarkable long-term stability. The X-ray absorption near-edge structure(XANES) and X-ray photoelectron spectrum(XPS) measurements confirmed the surface lattice oxygen created on the N-CuCoS1.97 NWs during OER. Then, the density function theory(DFT) results evident that lattice oxygen constructed surface of N-CuCoS1.97 NWs has more favorable OER energetic profiles and absorption for reaction intermediate. More importantly,the flexible and wearable Zn-air battery fabricated by the N-CuCoS1.97 NWs shows excellent rechargeable and mechanical stability, which can be used in portable mobile device.

Hierarchical N-Doped Porous Carbons for Zn–Air Batteries and Supercapacitors

Nitrogen-doped carbon materials with a large specific surface area,high conductivity,and adjustable microstructures have many prospects for energy-related applications.This is especially true for N-doped nanocarbons used in the electrocatalytic oxygen reduction reaction(ORR)and supercapacitors.Here,we report a low-cost,environmentally friendly,large-scale mechanochemical method of preparing N-doped porous carbons(NPCs)with hierarchical micro-mesopores and a large surface area via ball-milling polymerization followed by pyrolysis.The optimized NPC prepared at 1000°C(NPC-1000)offers excellent ORR activity with an onset potential(Eonset)and half-wave potential(E1/2)of 0.9 and 0.82 V,respectively(vs.a reversible hydrogen electrode),which are only approximately 30 mV lower than that of Pt/C.The rechargeable Zn–air battery assembled using NPC-1000 and the NiFe-layered double hydroxide as bifunctional ORR and oxygen evolution reaction electrodes offered superior cycling stability and comparable discharge performance to RuO2 and Pt/C.Moreover,the supercapacitor electrode equipped with NPC prepared at 800℃ exhibited a high specific capacity(431 F g^−1 at 10 mV s^−1),outstanding rate,performance,and excellent cycling stability in an aqueous 6-M KOH solution.This work demonstrates the potential of the mechanochemical preparation method of porous carbons,which are important for energy conversion and storage.