The Study On Porous Graphene/Metal Oxide Based Supercapacitor For Photoelectric Energy Storage

Energy storage and release is the key component in the photoelectric conversion system.Efficient energy storage devices play an extremely important role in promoting the performance of photovoltaic systems,new energy electric vehicles,etc.Supercapacitors,as a new type of energy storage device,have the features of fast charging,long cycle life,and high safety,etc.However,the low energy density of supercapacitors severely restricts their application prospect.As the key part of the supercapacitor,electrode materials are the core factor to affect the performance of the supercapacitor.Therefore,exploring and optimizing the electrode materials of supercapacitors is the most effective way to improve the performance of supercapacitors and achieve high energy density storage.Among many electrode materials,cobalt oxide(Co₃O₄)has shown great potential in electrochemical energy storage applications due to its ultra-high theoretical specific capacitance,but the low conductivity of Co₃O₄ and the expansion and contraction of the crystal in cycling make it exhibit low capacitance and poor cycle life in practical applications.The researchers found that combining graphene with Co₃O₄,using the excellent electrical conductivity of graphene and high specific capacitance of Co₃O₄ can effectively improve the energy storage capacity of the Co₃O₄/graphene composite.Nevertheless,tightly encapsulated Co₃O₄ by graphene makes the longer transportation pathway when ion interacted with Co₃O₄,which resulted in poor rate performance of the supercapacitor.In order to solve the disadvantage of the Co₃O₄ application in supercapacitors and improve the performance of Co₃O₄-based supercapacitors.In this work,using cubic Co₃O₄ as the research object and synthesizing holey graphene(HG)by making holes in the graphene oxide layer.Combined HG with Co₃O₄ to form Co₃O₄/HG which HG wrapped Co₃O₄ inside to provide high electric conductivity and unobstructed ions transportation pathway to improve rate performance.Optimized the mass ratio of Co₃O₄ to HG to achieve the best electrochemical storage properties and assembled the optimized Co₃O₄/HG into a supercapacitor to explore its energy storage in practical applications.The main research methods and results are as follows:Cubic Co₃O₄ nanocubes were prepared by hydrothermal method.HG was prepared by hydrogen peroxide etched graphene oxide and hydrothermally reduced.Without chemical etching only hydrothermally treated graphene oxide form reduced graphene oxide(RGO).The Co₃O₄ was combined with HG or RGO by hydrothermal method and Co₃O₄ was uniformly encapsulated in the three-dimensional interconnection network of HG or RGO.Finally,the composite material was deposited on Ni foil by electrophoretic deposition and as a binder-free electrode which is used in a supercapacitor.Tested by electrochemical workstation,the results showed that Co₃O₄/HG has better ion diffusion ability than Co₃O₄/RGO and Co₃O₄.Moreover,the Co₃O₄/RGO has a 3.5-fold increase in capacity compared to Co₃O₄ and Co₃O₄/HG-2 has a nearly 19-fold increase compared to Co₃O₄.Supercapacitors based on Co₃O₄/HG also showed excellent cycle performance,high power density and high energy density.