Preparation And Electrochemical Oxygen Evolution Research Of Cobalt Oxide Nanosheets

Recently,environmental pollution and energy security associated with reduced fossil fuels supply are increasingly prominent,finding clean and renewable energy sources has become one of the biggest challenges to sustainable social development.Hydrogen is recognized as an alternative fuel to meet growing global energy consumption due to its high specific energy and carbon neutral combustion products.The electrochemical water splitting has great potential in this field,and it is composed of two half reactions:hydrogen evolution reaction(HER)and oxygen evolution reaction(OER),which occur at the cathod and the anode,respectively.And therein OER with four-electron process become the rate-limiting step of the whole electrocatalytic water splitting process due to its slow kinetics.Up to now,noble metal-based materials,e.g.IrO2 and RuO2,are widely adopted as highly efficient OER catalysts.However,their limited abundance and high cost inevitably prevent their application in industrial processes.Therefore,it is very nescessay to develop new electrocatalysts with abundant earth reserves,high efficiency and low price.Two-dimensional transition metal oxides(2D TMOs)provide more active sites for catalytic reactions due to their large specific surface area and adjustable activity besides low cost and high stability.In this thesis,two-dementional cobalt-based oxides are used to study the effect of structural changes on the OER performance by adjusting the experimental conditions.The main research content is as follows:1.Co(OH)2 nanosheets are firstly prepared by solvothermal method and then calcined at 300,400 and 500 ? in air to obtain pore C03O4 nanosheets.The characterizations and the oxygen evolution performance show that the Co3O4 nanosheets calcined at 300 ? possess the largest specific surface area(93.02 m2 g-1),pore capacity(0.196 cm3 g-1)and more active sites.At the same time,the samples calcined at 300 ? exhibited the best OER performance:the onsetpotential and overpotential are 1.539 V and 0.37 V,respectively.And the Tafel slpoe is 49 mV dec-1.2.Co(OH)2 nanosheets are prepared firstly by solvthermal method,and then calcined at 250?,300 ? and 350 ? under the hydrogen atmosphere,and CoO nanosheets,CoO/Co nanocomposite and Co nanosheets are obtained,respectively.For CoO/Co nanocomposite,Co nanoparticles with a diameter of 100 nm are loaded on CoO nanosheets.The electrocatalytic properties show that the CoO/Co nanocomposite has the best OER performance:the onsetpotential and overpotential are 1.48 V and 0.325 V,respectively.And the Tafel slpoe is only 35 mV dec-1.The XPS and Raman analyses show that there is a strong interaction between Co and CoO in Co/CoO nanocomposite,and the synergistic effect of Co and CoO improves the OER performance of Co/CoO nanocomposite.In addition,the oxygen defects on the surface of CoO nanosheets are beneficial for OER performance.