Preparation Of High Performance Nanoporous Oxygen Evolution Film Materials At The Assist Of Electrodeposited SiO₂ As Template

With the improvement of living standards,and enhanced awareness of environmental protection,people eager to find new energy to solve the shortage of fossil energy and improve the environmental pollution problems caused due to abuse of fossil energy.Hydrogen is considered as one of the cleanest energy sources.Electrochemical water splitting is an important approach to produce hydrogen.However,the increased energy consumption caused by high oxygen evolution overpotential is the bottleneck during the preparation of hydrogen via electrochemical water splitting.Precious metal oxides,IrO₂ and RuO₂ are recognized as the best oxygen evolution electrode materials.Unfortunately,the scarce,expensive,and toxicity properties limit their large-scale commercial applications.In recent years,people have been committed to develop new catalyst materials,such as,the oxides or hydroxides of manganese,cobalt,and nickel,which are low cost,earth abundant,but with high catalytic performance and good stability in alkaline environment to replace the precious metal oxide.Additionally,high specific surface area is also benefit to enhance the oxygen evolution performance of a catalyst.Templated strategy which can effectively improve the surface area of the nanoporous electrode material has attracted a great deal of attention.In this thesis,nanoporous nickel-cobalt based film electrodes were prepared via electrodeposited SiO₂ as template.Structure and morphology of the films were characterized by scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?.Electrocatalytic oxygen evolution activity and stability of the electrodes were investigated by electrochemical measurements.In the third chapter,Ni?NO3?2,Co?NO3?2 and Tetramethoxysilane?TMOS?were used to prepare the precursor solution.Nickel and cobalt hydroxides were prepared on stainless steel substrate by galvanostatic deposition,and then NiCo2O4-SiO₂ composite films were obtained after heat treatment.The SiO₂ template was removed by continuous cyclic voltammetry in 1.0 mol L-1 KOH solution in order to obtain porous NiCo2O4 films.The effects of deposition current density,deposition time and TMOS concentration on the oxygen evolution electrocatalytic activiy were investigated.Results show that the films prepared at a current density of-1.0 mA cm-2 in 1.0% TMOS solution for 500 s have the highest oxygen evolution activity and stability.The onset potential of the electrode is 1.52 V?vs.RHE?.The overpotentials are 0.293 V and 0.358 V under the current densities at 10 and 100 mA cm-2,respectively.The Tafel slopes are 43 and 142 mV dec-1,respectively.In the fourth chapter,Ni-Co-SiO₂ composite thin films were prepared onto stainless steel substrate by potentiostatic method in a precursor solution containing NiSO4,CoSO4 and TMOS.Results indicate that the component concentration in the solution,electrodeposition potential and duration time have great influence on the microstructure and oxygen evolution performance for the film electrodes.The porous nickel-cobalt alloy film electrodes deposited at-0.8 V for 500 s have excellent electrocatalytic performance and stability.The onset potential of the electrode is 1.48 V?vs.RHE?.The overpotentials are 0.287 V and 0.326 V under the current densities at 10 and 100 mA cm-2,respectively.The Tafel slopes are 65 and 149 mV dec-1,respectively.In the fifth chapter,in order to solve the poor compatibility of alcohol-soluble TMOS with many inorganic salts,we proposed to prepare porous nickel-cobalt-based film electrodes with water-soluble ammonium fluorosilicate as silicon source.The effects of electrodeposition time and components concentration on the electrocatalytic performance of nickel-cobalt alloy electrodes were investigated.Results show that ammonium fluorosilicate has good compatibility with many nickel and cobalt salt solution systems,and can be efficiently used to prepare composite film electrodes with improved electrocatalytic activity of the electrodes are improved.The onset potential of the electrode is 1.48 V?vs.RHE?.The overpotentials are 0.294 V and 0.336 V under the current densities at 10 and 100 mA cm-2,respectively.The Tafel slopes are 39 and 137 mV dec-1,respectively.