FeCo alloy/N,S dual-doped carbon composite as a high-performance bifunctional catalyst in an advanced rechargeable zinc-air battery

The rational design and development of cost-effective,high-performance,and stable bifunctional oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)electrocatalysts are essential for rechargeable zinc-air batteries.Herein,a novel FeCo composite composed of alloy nanoparticles embedded in an N,S dual-doped carbon matrix(FeCo/NSC)was prepared via one-step carbonization of amphiphilic dodecanethiol-metal salts wrapped in carbon nitride(C_(3)N_(4)).The compact combination of dual metalalloys and dual-doped carbon endowed the composite with the active sites for the ORR and OER,achieving efficient electrical transmission and highly efficient bifunctional catalytic performance.The obtained FeCo-1/NSC catalyst exhibited excellent electrocatalytic activity with a half-wave potential of 0.82 V(vs.RHE)for the ORR and a low overpotential of 0.325 V at 10 mA cm^(-2) for the OER.The liquid Zn-air battery with FeCo-1/NSC as an air electrode displayed excellent charge-discharge performance,high power density,and robust charge-discharge stability for 150 h compared to the 20%Pt/C+RuO_(2) counterpart.Furthermore,the FeCo-1/NSC-based flexible solid-state Zn-air battery exhibited a higher power density and good charge-discharge stability over 10 h of operation.Thus,a promising strategy for bifunctional electrocatalyst development as part of rechargeable and wearable Zn-air batteries was provided.

Nitrogen-doped carbon nanotube encapsulating cobalt nanoparticles towards efficient oxygen reduction for zinc–air battery

Nitrogen-doped carbon materials encapsulating 3 d transition metals are promising alternatives to replace noble metal Pt catalysts for efficiently catalyzing the oxygen reduction reaction(ORR). Herein, we use cobalt substituted perfluorosulfonic acid/polytetrafluoroethylene copolymer and dicyandiamide as the pyrolysis precursor to synthesize nitrogen-doped carbon nanotube(N–CNT) encapsulating cobalt nanoparticles hybrid material. The carbon layers and specific surface area of N–CNT have a critical role to the ORR performance due to the exposed active sites, determined by the mass ratio of the two precursors. The optimum hybrid material exhibits high ORR activity and stability, as well as excellent performance and durability in zinc–air battery.

Development of flexible zinc–air battery with nanocomposite electrodes and a novel separator

In this paper, we present the development of flexible zinc–air battery. Multiwalled carbon nanotubes(MWCNTs) were added into electrodes to improve their performance. It was found that MWCNTs were effective conductive additive in anode as they bridged the zinc particles. Poly(3,4-ethylenedioxythiophene)polystyrene sulfonate(PEDOT:PSS) was applied as a co-binder to enhance both the conductivity and flexibility. A poly(acrylic acid)(PAA) and polyvinyl alcohol(PVA) coated paper separator was used to enhance the battery performance where the PVP–PAA layer facilitated electrolyte storage. The batteries remained functional under bending conditions and after bending. Multiple design optimizations were also carried out for storage and performance purposes.

Boosting electrocatalytic activity with the formation of abundant heterointerfaces and N, S dual-doped carbon nanotube for rechargeable Zn-air battery

Herein,a facile synthetic strategy is proposed to fabricate high-performance electrocatalysts for rechargeable Zn-air batteries(ZABs).Heterostructured NiCo/NiCo_(2)S_(4) nanoparticles encapsulated in N-,S-co-doped CNT(NiCo/NiCo_(2)S_(4)@NSCNT) are synthesized via co-precipitation,thermal carbonization,and partial sulfidation processes.The strongly coupled NiCo/NiCo_(2)S_(4) heterostructure can improve the redox property and charge transfer ability.Also,the CNTs with abundant foreign dopants provide high electrical conductivity and abundant defect sites for both the oxygen evolution reaction(OER) and oxygen reduction reaction(ORR).The prepared NiCo/NiCo_(2)S_(4)@NSCNT electrocatalyst exhibits a low overpotential of 349 mV at a current density of 10 mA cm-2 and a half-wave potential of 0.865 V for the OER and ORR,respectively.Moreover,the ZAB assembled using as-prepared NiCo/NiCo_(2)S_(4)@NSCNT can provide superior specific capacity(756.16 mA h g_(Zn)^(-1)],peak power density(155.82 mW cm^(-2)),and long-term cyclability compared to those of the precious metal-based electrocatalyst(Pt/C+RuO_(2)).

Lamellar-stacked cobalt-based nanopiles integrated with nitrogen/sulfur co-doped graphene as a bifunctional electrocatalyst for ultralong-term zinc-air batteries

Sluggish oxygen evolution reaction(OER)and oxygen reduction reaction(ORR)kinetics inevitably impede the practical performance of rechargeable zinc-air batteries.Thus,combing the structural designability of transition metal-based electrocatalysts with anionic regulation is highly desired.Herein,mesoporous lamellar-stacked cobalt-based nanopiles with surface-sulfurization modification are elaborately designed and integrated with N/S co-doped graphene to build a robust OER/ORR bifunctional electrocatalyst.The lamellar-stacking mode of mesoporous nanosheets with abundant channels accelerates gas-liquid mass transfer,and partial-sulfurization of cobalt-based matrix surface efficiently improves the intrinsic OER activity.Meanwhile,N/S co-doped graphene further reinforces the ORR active sites while providing a stable conductive skeleton.As expected,this composite electrocatalyst delivers considerable bifunctional activity and stability,with an OER overpotential of 323 m V at 10 m A cm^(-2)and high durability.When applied in zinc-air batteries,remarkable ultralong-term stability over 4000 cycles and a maximum power density of 150.1 m W cm^(-2)are achieved.This work provides new insight into structurecomposition synergistic design of rapid-kinetics OER/ORR bifunctional electrocatalyst for nextgeneration metal-air batteries.

Dynamic stretching–electroplating metal-coated textile for a flexible and stretchable zinc–air battery

A metal electrode is a significant component of a zinc–air battery(ZAB),but the metal material is usually not elastic,which severely restricts the application of flexible and stretchable ZABs in the field of wearable electronic devices.Herein,we report a flexible and stretchable metal-coated textile prepared by a dynamic stretching–electroplating based on a wavy spandex textile substrate.Benefiting from the unique woven and wavy structure,the metal-coated textile shows a high stretchability of 100%and stable conductivity.In situ scanning electron microscope observation during stretching showed that the tensile strain of the metal-coated textile is mainly attributed to the deformation of the microfiber network at the bottom position of the wave structure.In addition,a sodium carboxymethyl cellulose–polyacrylic acid–potassium hydroxide composite hydrogel has been used as the electrolyte.This hydrogel shows excellent ionic conductivity,mechanical properties,and water retention properties,which makes it suitable for the semi-open system of ZAB.Furthermore,a flexible and stretchable sandwich-structure ZAB,assembled using the above-mentioned electrodes and electrolyte,operates stably even under rapid stretching/releasing cycle deformation.Because of its facile preparation and low cost,this flexible and stretchable ZAB is suitable for fabrication of large-area batteries to obtain higher output current and power to drive wearable electronic devices.

Co_(2)N Nanoparticles Anchored on N-Doped Active Carbon as Catalyst for Oxygen Reduction Reaction in Zinc–Air Battery

The development of efficient catalytic electrode toward oxygen reduction reaction(ORR)is still a great challenge for the wide use of zinc–air batteries.Herein,Co_(2)N nanoparticles(NPs)anchored on N-doped carbon from cattail were verified with excellent catalytic performances for ORR.The onset and half-wave potentials over the optimal catalyst reach to 0.96 V and 0.84 V,respectively.Current retention rates of 96.8%after 22-h test and 98.8%after running 1600 s were obtained in 1 M methanol solution.Density functional theory simulation proposes an apparently increased electronic states of Co_(2)N in N-doped carbon layer close to the Fermi level.Higher charge density,favorable adsorption,and charge transfer of intermediates originate from the coexistence of Co_(2)N NPs and N atoms in carbon skeleton.The superior catalytic activity of composites also was confirmed in zinc–air batteries.This novel catalytic property and controllable preparation approach of Co_(2)Ncarbon composites provide a promising avenue to fabricate metal-containing catalytically active carbon from biomass.

Hierarchical Carbon Microtube@Nanotube Core-Shell Structure for High-Performance Oxygen Electrocatalysis and Zn-Air Battery

Zinc-air batteries(ZABs)hold tremendous promise for clean and efficient energy storage with the merits of high theoretical energy density and environmental friendliness.However,the performance of practical ZABs is still unsatisfactory because of the inevitably decreased activity of electrocatalysts when assembly into a thick electrode with high mass loading.Herein,we report a hierarchical electrocatalyst based on carbon microtube@nanotube core-shell nanostructure(CMT@CNT),which demonstrates superior electrocatalytic activity for oxygen reduction reaction and oxygen evolution reaction with a small potential gap of 0.678 V.Remarkably,when being employed as air-cathode in ZAB,the CMT@CNT presents an excellent performance with a high power density(160.6 mW cm^−2),specific capacity(781.7 mAhgZn^−1)as well as long cycle stability(117 h,351 cycles).Moreover,the ZAB performance of CMT@CNT is maintained well even under high mass loading(3 mg cm−2,three times as much as traditional usage),which could afford high power density and energy density for advanced electronic equipment.We believe that this work is promising for the rational design of hierarchical structured electrocatalysts for advanced metal-air batteries.

Cobalt-doped Mn3O4 nanocrystals embedded in graphene nanosheets as a high-performance bifunctional oxygen electrocatalyst for rechargeable Zn–Air batteries

A non-noble-metal bifunctional catalyst with efficient and durable activity towards both the oxygen reduction reaction(ORR)and the oxygen evolution reaction(OER)is crucial to the development of rechargeable Zn-air batteries.Herein,a facile one-step hydrothermal method is reported for the synthesis of a high-performance bifunctional oxygen electrocatalyst,cobalt-doped Mn_(3)O_(4) nanocrystals supported on graphene nanosheets(Co–Mn_(3)O_(4)/G).Compare to pristine Mn_(3)O_(4),this Co–Mn_(3)O_(4)/G exhibits greatly enhanced electrocatalytic activity,delivering a halfwave potential of 0.866 V for the ORR and a low overpotential of 275 mV at 10 mA cm^(-2) for the OER.The zinc-air battery built with Co–Mn_(3)O_(4)/G shows a reduced charge–discharge voltage of 0.91 V at 10 mA cm^(-2),an power density of 115.24 mW cm^(-2) and excellent stability without any degradation after 945 cycles(315 h),outperforming the state-of-the-art Pt/C–Ir/C catalyst-based device.

A post-modification strategy to precisely construct dual-atom sites for oxygen reduction electrocatalysis

Dual-atom catalysts(DACs) afford promising potential for oxygen reduction electrocatalysis due to their high atomic efficiency and high intrinsic activity.However,precise construction of dual-atom sites remains a challenge.In this work,a post-modification strategy is proposed to precisely fabricate DACs for oxygen reduction electrocatalysis.Concretely,a secondary metal precursor is introduced to the primary single-atom sites to introduce direct metal-metal interaction,which ensures the formation of desired atom pair structure during the subsequent pyrolysis process and allows for successful construction of DACs.The as-prepared FeCo-NC DAC exhibits superior oxygen reduction electrocatalytic activity with a half-wave potential of 0,91 V vs.reversible hydrogen electrode.Zn-air batteries equipped with the FeCo-NC DAC demonstrate higher peak power density than those with the Pt/C benchmark.More importantly,this post-modification strategy is demonstrated universal to achieve a variety of dual-atom sites.This work presents an effective synthesis methodology for precise construction of catalytic materials and propels their applications in energy-related devices.

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.

Strengthening absorption ability of Co-N-C as efficient bifunctional oxygen catalyst by modulating the d band center using MoC

Co-N-C is a promising oxygen electrochemical catalyst due to its high stability and good durability.However,due to the limited adsorption ability improvement for oxygen-containing intermediates,it usually exhibits inadequate catalytic activity with 2-electron pathway and high selectivity of hydrogen peroxide.Herein,the adsorption of Co-N-C to these intermediates is modulated by constructing heterostructures using transition metals and their derivatives based on d-band theory.The heterostructured nanobelts with MoC core and pomegranate-like carbon shell consisting of Co nanoparticles and N dopant(MoC/Co-N-C)are engineered to successfully modulate the d band center of active Co-N-C sites,resulting in a remarkably enhanced electrocatalysis performance.The optimally performing MoC/Co-N-C exhibits outstanding bi-catalytic activity and stability for the oxygen electrochemistry,featuring a high wave-half potential of 0.865 V for the oxygen reduction reaction(ORR)and low overpotential of 370 mV for the oxygen evolution reaction(OER)at 10 mA cm^(-2).The zinc air batteries with the MoC/Co-N-C catalyst demonstrate a large power density of 180 mW cm^(-2)and a long cycling lifespan(2000 cycles).The density functional theory calculations with Hubbard correction(DFT+U)reveal the electron transferring from Co to Mo atoms that effectively modulate the d band center of the active Co sites and achieve optimum adsorption ability with"single site double adsorption"mode.

FeCo-N encapsuled in nitrogen-doped carbon nanotubes as bifunctional electrocatalysts with a high stability for zinc air batteries

For zinc air batteries,a non-noble metal-based electrocatalyst with a high performance and stability in oxygen evolution reaction(OER)and oxygen reduction reaction(ORR)is imperative in application.Herein,a catalyst based on FeCo-N encapsuled in nitrogen-doped carbon nanotubes has been prepared,which provides an implementable method to design controlled structures with excellent bifunction al electrocatalytic activities.By adjusting the molar ratio of two metals,the synthesized FeCo-N-C catalyst delivers a competitive ORR and OER performance compared with commercial Pt/C and IrO_(2),performing a low overvoltage gap between ORR(E_(1/2))and OER(E_(j=10))of 0.8 V.Moreover,as a promising cathode in zinc air battery,the FeCo-N-C catalyst possesses an affirmative stability of over 100 h and large power density(129 mW·cm^(-2)).This work demonstrates that FeCo-N-C is one of the most promising catalysts for zinc air batteries and provides a possibility for exploration of batteries with high stability by adjusting the molar ratio of metals in the catalysts.

Cryogenic electrolytes and catalysts for zinc air batteries

The challenges of enabling zinc air batteries to operate at ultralow temperatures are twofold.The Prerequisite is preventing the electrolyte from freezing while maintaining high ionic conductivity.Secondly,the catalyst has to work efficiently at low temperatures.This highlight presents the latest development to resolve the challenges by tuning the structures of the electrolyte and catalyst,offering a new paradigm to widen the working temperature range of zinc air batteries.

Heterointerface engineering of assembled CoP_(2) on N-modified carbon as efficient trifunctional electrocatalysts for Zn-Air batteries and overall water splitting

Enhancing catalytic activity through modulating the interaction between N-doped carbon and metal phosphides clusters is an effective approach.Herein,the electronic structure modulation of CoP_(2) supported N-modified carbon(CoP_(2)/NC)has been designed and prepared as efficient electrocatalysts for oxygen reduction reaction(ORR),oxygen evolution reaction(OER),and hydrogen evolution reaction(HER).Notably,CoP_(2)/NC-1 catalyst exhibits impressive performance in alkaline media,with an ORR half-wave potential of 0.84 V,as well as OER and HER overpotentials of 290 and 129 mV(at 10 mA·cm^(−2)),respectively.In addition,CoP_(2)/NC-1 produces a power density as high as 172.9 mW·cm^(−2),and excellent reversibility of 100 h at 20 mA·cm^(−2) in home-made Zn-air batteries.The experimental results demonstrate that the synergistic interactions between N modified carbon substrate and CoP_(2) material significantly enhance the kinetics of ORR,OER,and HER.Density functional theory(DFT)calculations reveal the strong electrons redistribution of CoP_(2) induced by high-density N atoms at the interface,thus optimizing the key intermediates and significantly lower the energy barrier of reactions.These electronic adjustments of CoP_(2) greatly enhance its kinetics of ORR/OER/HER,leading to faster reactions.This study provides profound insights into the specific modification of CoP_(2) by N-doped carbon,enabling the construction of efficient catalysts.

Bead-like cobalt-nitrogen co-doped carbon nanocage/carbon nanofiber composite:A high-performance oxygen reduction electrocatalyst for zinc-air batteries

Proper regulation of metal-nitrogen carbon(M-N-C)materials derived from zeolitic imidazolate frameworks(ZIFs)is essential to enhance the oxygen reduction reaction(ORR)performance.However,most of the reports focus on the component regulation,and the structure regulation of ZIFs-derived M-N-C materials by a simple preparation method has been barely reported.Herein,using a one-step electrospinning method with subsequent pyrolysis,we have prepared a bead-like cobalt-nitrogen co-doped carbon nanocage/carbon nanofiber(Co-N-C/CNF)composite electrocatalyst with the porous carbon nanocages arranged one by one in the highly conductive carbon nanofibers.Profiting from the fully exposed active sites and improved conductivity,the Co-NC/CNF catalyst exhibits an excellent ORR performance even surpassing the commercial Pt/C catalyst.Density functional theory(DFT)results demonstrate that the CoNP-N1-C2 active sites on Co-N-C/CNF make the core contribution to the improvement of ORR properties.Moreover,the zinc-air battery(ZAB)based on the Co-N-C/CNF catalyst also shows outstanding discharge performance.This study provides a new strategy for the preparation and structural design for ZIFs-derived M-N-C materials as efficient ORR catalysts.

Low-Temperature Working Feasibility of Zinc–Air Batteries with Noble Metal-Free Electrocatalysts

Expanding the application scenario for rechargeable batteries is the key to the terminal utilization of renewable energy.Enabling zinc–air batteries at low temperatures is drawing increasing attention,yet the low-temperature working feasibility of zinc–air batteries with noble metalfree electrocatalysts remains indistinct.In this contribution,the low-temperature performances of zinc–air batteries with noble metal-free electrocatalysts are comprehensively investigated.Armed with a representative noble metal-free bifunctional oxygen electrocatalyst,the zinc–air batteries demonstrate satisfactory yet relatively depressed performance at low temperatures,compared with that at room temperatures.The reduced electrolyte conductivity is identified as one of the limiting factors for the reduced low-temperature performance.Furthermore,electrolyte engineering via solvation structure regulation is performed on the zinc–air batteries with noblemetal-free electrocatalysts,where an improved low-temperature performance is achieved.This work reveals the compatibility between noble metal-free electrocatalysts and low-temperature feasibility/low-temperature performance enhancement strategies for zinc–air batteries and affords new opportunities to satisfy low-cost and efficient energy storage at harsh working conditions.

Advanced polymer-based electrolytes in zinc-air batteries

Zinc–air batteries(ZABs)are expected to be some of the most promising power sources for wearable and portable electronic devices and have received widespread research interest.As an ion conductor connecting anodes and cathodes,the electrolyte is critical for the overall performance of ZABs(e.g.,energy density,rechargeability,and operating voltage).Compared with liquid electrolytes,polymer-based electrolytes have superior characteristics for ZABs,such as negligible electrolyte leakage,three-phase interface stabilization,and dendrite suppression.In this perspective,we focus on recent progress in polymer-based electrolytes for ZABs.After a brief introduction to ZABs and electrolytes,we emphasize the development of polymer-based electrolytes in terms of their intrinsic properties and interfacial chemistry.Finally,challenges and viable strategies are proposed for polymer-based electrolytes in ZABs.We hope that this work will provide useful guidance to spur the development of high-performance ZABs based on advanced polymer-based electrolytes.

FeCo alloy/N,S co-doped carbon aerogel derived from directionalcasting cellulose nanofibers for rechargeable liquid flow and flexible Zn–air batteries

Bifunctional oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)electrocatalysts with the advantages of excellent activity and stability are the vital components of air cathodes for rechargeable Zn–air batteries(ZABs).Herein,the carbon aerogel with honeycomb-like structure,N and S double doping and loaded with FeCo alloy nanoparticles(NSCA/FeCo)was prepared successfully as cathodes for rechargeable liquid flow and two-dimensional flexible ZABs by clever directional casting.The interaction between the bimetallic alloy and the double-doped carbon with specifical structure,large surface,great conductivity endows NSCA/FeCo with effective ORR/OER active sites and small charge/mass transport barrier,thus achieving outstanding bifunctional catalytic performance.The NSCA/FeCo displays a half-wave potential of+0.85 V(vs.reversible hydrogen electrode(RHE))for ORR and an overpotential of 335 mV at a current density of 10 mA·cm^(−2)for OER,which is even comparable to the performance of noble-metal catalysts in relevant fields(Pt/C for ORR and RuO_(2)for OER).Consequently,the rechargeable liquid flow ZABs assembled with NSCA/FeCo showed excellent performance(maximum power density:132.0 mW·cm^(−2),specific capacity:804.5 Wh·kg^(−1)at 10 mA·cm^(−2),charge and discharge cycle stability of more than 250 cycles).Furthermore,the flexible NSCA/FeCo-based ZABs have a maximum power density of 43.0 mW·cm^(−2),outstanding charging–discharge stability of more than 450 cycles,exhibit good flexibility under different bending conditions.Therefore,this work has provided an efficient bifunctional electrocatalyst for OER/ORR and a promising strategy of air cathodes for rechargeable and wearable ZABs.

Neuron-inspired design of hierarchically porous carbon networks embedded with single-iron sites for efficient oxygen reduction

The rational structure design and active-site regulation of catalysts is crucial for high energy output. Herein, B, F co-doped Fe–N–C embedded in a flexible and free-standing hierarchical porous carbon framework(Fe–SA–FPCS) was reported. Owing to the synergism of optimized intrinsic activity, fast mass transfer and well exposed active sites, the Fe–SA–FPCS exhibits a high halfwave potential(E1/2=0.89 V vs. RHE) and small Tafel slope(66 m V dec^(-1)). Theoretical calculations uncover that B, F co-doping could accelerate the desorption of OH* on Fe sites, which can effectively increase oxygen reduction reaction activity. As the cathode for Zn–air batteries(ZABs), Fe–SA–FPCS demonstrates a high open-circuit voltage(1.51 V), large peak power density(168.4 m W cm^(-2)) and excellent stability. The assembled flexible solid-state ZAB exhibits excellent stability during charge and discharge cycling in the flat/bent state, and is promising for the application of portable and flexible devices. This work provides a new perspective for the fabrication of single-atom electrocatalysts with well-designed structure and excellent electrochemical energy conversion and storage capability.