Two-dimensional Cobalt-based Bimetallic Compounds For Electrocatalysis Performance

The over-exploitation and use of traditional fossil energy has led to an increasingly prominent energy crisis and environmental problems,and also poses a serious threat to the survival and development of mankind.Therefore,it is very important to research and develop clean energy to find efficient,clean,and renewable energy.The current scientific and technological equipment used for clean energy conversion,such as fuel cells,metal-air batteries and electrolyzed water,etc.The common core of these energy conversion technologies is a series of electrochemical processes.It mainly involves three key electrocatalytic reactions,namely hydrogen evolution reaction（Hydrogen evolution reaction,HER）,oxygen evolution reaction（Oxygen evolution reaction,OER）and oxygen reduction reaction（Oxygen reduction reaction,ORR）.However,the slow kinetics of HER,OER,and ORR and their dependence on precious metal-based catalysts（such as Pt,Ir,and Ru）hinder the large-scale commercial application of these devices.Therefore,there is an urgent need to develop low-cost,efficient,stable and scalable electrocatalysts.Because of its abundant reserves,low cost,excellent catalytic performance,and excellent cycle stability,transition metal-based catalysts are considered to be one of the ideal alternative materials for noble metal-based catalysts.In this paper,the low-cost,high-activity and abundant raw material cobalt-based transition metals are selected as the research object,and the physical and chemical properties of the materials are controlled by using different synthesis strategies,and the catalytic performance of the synthesized catalysts for HER,OER and ORR,and its use in zinc air battery and electrolyzed water.The main research contents are as follows:（1）A novel two-dimensional sulfur-rich vacancy copper-cobalt sulfide sheet structure（CuCo₂S₄ NSs）was synthesized by a simple chemical etching strategy.Studies have found that CuCo₂S₄ NSs has a large number of oxygen vacancies,a large specific surface area and stable active sites.Therefore,CuCo₂S₄ NSs exhibits excellent catalytic performance for ORR and OER in alkaline electrolyte,which is comparable to commercial Pt/C and Ru O₂ catalysts.As an air cathode,the zinc-air battery driven by CuCo₂S₄-10_OH-200 NSs is better than the traditional Pt/C+Ru O₂ air cathode driven zinc-air battery,which has a greater peak power density(183.2 m W cm^-2)and high energy Density(966.1 Wh kg^-1)and excellent cycle stability.（2）The copper-cobalt composite sulfide/cobalt phosphide heterostructure（CuCo₂S₄/Co₂P）was synthesized through a simple hydrothermal method and partial phosphating treatment strategy.Studies have shown that CuCo₂S₄/Co₂P has a heterogeneous structure and multiple active components.The obvious interface coupling between CuCo₂S₄and Co₂P,and the electronic coupling between copper and cobalt all promote the excellent electrocatalytic activity of CuCo₂S₄/Co₂P for OER and HER and long-term stability in alkaline media.By using the CuCo₂S₄/Co₂P heterostructure as the cathode and anode at the same time,a current density of 10 m A cm^-2 can be driven with only a battery voltage of 1.55V,and the overall water splitting can be achieved.（3）CuCo₂S₄ TSA spinel nanosheets CuCo₂S₄ uniformly grown on carbon felt were prepared by a one-step hydrothermal method.The research results show that due to the coordination effect of the metal species and the highly conductive carbon framework and the presence of the carbon felt substrate,the specific surface area of the material is increased,the conductivity is enhanced,and the catalytic activity is promoted.Therefore,the CuCo₂S₄ TSA composite exhibits excellent bifunctional catalytic performance and excellent stability in alkaline electrolytes.At a current density of 10 m A cm^-2,the OER overpotential is 0.21 V,and the HER overpotential is 0.069 V.It is equivalent to commercial Ru O₂ and Pt/C catalysts.In summary,this article synthesized high-performance CuCo₂S₄ NSs,CuCo₂S₄/Co₂P and CuCo₂S₄ TSA dual-functional catalysts through a simple preparation process.By adopting different strategies,the active components,morphology and surface defects of the materials were controlled,and the catalytic performance of the materials on ORR,OER and HER was analyzed.In addition,using the material as a catalyst for the air cathode can drive the zinc-air battery well and exhibit excellent performance;using the material as the cathode and anode of the water electrolysis device can efficiently decompose water under low battery voltage.This thesis brings new opportunities for the design and development of high-efficiency cobalt-based dual-function electrocatalysts used in rechargeable zinc-air batteries and water electrolysis devices.