Design Of High-efficiency Electrocatalyst Based On Interface Regulation Of Transition Metal Sulfide And Exploration Of Its Application

The energy crisis and environmental problems caused by the heavy use of fossil fuels have urged people to look for clean energy and efficient energy storage devices to replace traditional energy sources.Among them,Zn-air batteries（ZABs）are assumed that be a potential energy storage device due to their high theoretical energy density(1086 Wh kg^-1),safety,and environmental friendliness.Abundant Zn resources and unlimited supply ofO₂ in the air have made ZABs a research hotspot.Oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）reactions occur in ZABs.However,the ion/electron transport kinetics of the above two reactions are slow,resulting in lower energy conversion efficiency,which requires the addition of catalysts.At present,commercial catalysts are Pt/C,Ir/C and RuO₂,although they have excellent electrocatalytic performance,but due to high cost,and only have a single catalytic activity,the lack of dual functionality has led to serious restrictions on their application.Therefore,the current research focus on catalysts applied to ZABs is on the construction of low-cost and high-performance bi/trifunctional catalysts.According to literature,atoms with insufficient M-S bond coordination in transition metal sulfides（TMS）exhibit better catalytic performance.Compared with precious metal catalysts,TMS has more abundant resources,lower cost and better stability.Compared with oxides,the band gap energy of S is mostly lower than that of the corresponding oxides,and more importantly,the electronegativity of S is lower than that of O,resulting in weak covalent properties of M-S bonds,which are easier to break than M-O bonds under electrochemical conditions.It has higher corrosion resistance compared to metal-free carbon materials;Compared to metal phosphides,most TMS are semiconductors with higher conductivity and tunable bands.However,the intrinsic conductivity of TMS is not high,and nanoparticles are easy to aggregate,which affect the further development and utilization of TMS.Based on the above problems,we have done the following work:1.The Ni₃[Co（CN）₆]₂ precursor was synthesized using K₃[Co（CN）₆],that is,K⁺in K₃[Co（CN）₆]was completely replaced by Ni²⁺.Then,grow Co（OH）₂ on the surface of Ni₃[Co（CN）₆]₂.After vulcanizing Ni₃[Co（CN）₆]₂/Co（OH）₂ precursor,a porous NiCoS_x/CoS₂ composite catalyst material with cubic structure was obtained.The introduction of Ni improves the electronic structure and increases the inherent electrocatalytic activity.Co（OH）₂ covers the surface of Ni₃[Co（CN）₆]₂,preventing structural collapse and aggregation of Ni₃[Co（CN）₆]₂ frame structures during heat treatment.NiCoS_x/CoS₂ exhibits an overpotential of 310 mV at 20 mA cm^-2 with a half-wave potential of 0.80 V.During the HER test,the catalyst showed an overpotential of253 mV at 10 mA cm^-2.The catalyst not only has excellent ORR,OER and HER three-function electrocatalytic performance,but also shows very stable catalytic performance in ZABs.ZABs assembled with NiCoS_x/CoS₂ were stably charged and discharged for 630cycles at 5 mA cm^-2 with a charge/discharge overpotential gap of 0.8 V.At the same time,we also tested the application of the catalyst in flexible batteries.The flexible battery assembled based on NiCoS_x/CoS₂ catalyst can maintain stable charge and discharge for15 h（45 cycles）under at 5 mA cm^-2.Flexible batteries can be reliably cycled at any bending angle.This illustrates the feasibility of its application in flexible batteries and wearable products.2.A hollow tubular Co₃S₄/NiS/FeS heterogeneous composite material was prepared by ordinary hydrothermal method.The internal Co₃S₄ can be used as the carrier of external NiS/FeS,and the external NiS/FeS can effectively prevent the collapse of the hollow structure of internal Co₃S₄.The strong electron interaction between Co₃S₄ and NiS/FeS significantly increases its catalytic activity.Only an overpotential of 230 mV is required to achieve a current density of 10 mA cm^-2,which is superior to commercial RuO₂.When Co₃S₄/NiS/FeS is applied to ZABs,it exhibits a high power density of179.86 m W cm^-2 and a large specific capacity of 747 mA h g^-1.At a current density of 3mA cm^-2,there are 2700 stable cycles with a voltage gap of only 0.67 V.When applied in flexible batteries,it can be discharged/charged at any bending angle.In addition,Co₃S₄/NiS/FeS also showed good HER activity,showing a low overpotential of 233 mV at 10 mA cm^-2,and in the process of water electrolysis,using Co₃S₄/NiS/FeS as the anode and cathode electrocatalyst,only 1.52 V voltage can reach a current density of 10 mA cm^-2,and the catalytic activity remains stable within 50 h.In summary,Co₃S₄/NiS/FeS is a potential trifunctional catalyst for ZABs and water electrolysis.3.On the basis of the second work,the hollow tubular NiCo₂S₄ material were made,and Ni²⁺was introduced into the system to replace part of the Co²⁺in the Co₃S₄ hollow tubes,and the catalytic performance of binary metal sulfides was explored.By introducing multiple metals,the number of exposed active sites can be increased with the help of synergistic effects between various transition metals,thereby improving electrocatalytic performance.The unique hollow structure not only facilitates the penetration of electrolyte,accelerates electron/ion mass transfer,but also ensures that NiCo₂S₄ maintains structural stability and performance stability in cyclic charge-discharge tests.At 10 mA cm^-2,NiCo₂S₄ has an overpotential of 240 mV.The half-wave potential during ORR is 0.79 V andΔE is only 0.68 V.When NiCo₂S₄ is applied to ZABs,the stable cycle is 1200 cycles（400 h）at 3 mA cm^-2 and 600 cycles（200 h）at 5 mA cm^-2.The results show that NiCo₂S₄ has potential application prospects in ZABs.