The Design And Preparation Of Semiconductor-based Materials For Photocatalytic Water Splitting

With the rapid development of industry,environmental pollution and energy shortage have become the primary challenge to human beings.Developing clean and sustainable energy is an ideal strategy to solve the current problem.Solar energy is not only the ultimate source of energy for life on the earth,but also a major source of energy for fossil fuels,possessing aboundant,environment-friendly and safety characteristics.Converting it into clean energy can effectively reduce the dependence on fossil fuels and realize a bright future for sustainable energy development.Photocatalytic（PC）and photoelectrochemical（PEC）water splitting technology are considered to be one of the most effective strategies to realize solar-to-chemical energy conversion.Semiconductor-based photocatalysis has attracted much attention since photoelectrochemical water splitting is discovered for the first time in1972.Among the materials for photocatalytic H₂ generation from water splitting,graphitic carbon nitride（g-C₃N₄）has attracted much attention because of its moderate bandgap,low cost and appealing chemical stability.Unfortunately,it still faces a long way to meet the practical requirements on account of its fast recombination of photo-induced electrons and holes.Therefore,accelerating the separation and transfer of charges and suppressing their recombination is the key to improve photocatalytic performance.Loading co-catalysts or constructing heterostructures are considered as one of the most promising methods to improve its photocatalytic efficiency.Monoclinic BiVO₄ has been regarded as one of the ideal photoanode matericals for photoelectrochemical water oxidation due to its small band gap and good stability.Theoretically,its solar-to-hydrogen（STH）conversion efficiency is about 9.2%and the photocurrent intensity is about 7.5 mA cm^-2.However,the actual efficiency is still much lower,because of its poor carrier mobility,slow water oxidation kinetics and more positive conduction band position.Therefore,how to accelerate transportation of photogenerated carriers and inhibit their recombination becomes the major problem in a PEC reaction.Loading co-catalysts can significantly reduce the activation energy of the rate-determining step in the water oxidation process and promote carriers’transportation,resulting in the enhanced water oxidation kinetics and carriers separation,thus achieving excellent photoelectrochemical performance.In view of the above problems,the research contents of this paper are as follows:The study on the preparation and the photocatalytic H₂ generation of amorphous Ni₂P₂O₇ modified g-C₃N₄:a-Ni₂P₂O₇/g-C₃N₄ is successfully prepared by calcining a mixture of NiNH₄PO₄?H₂O and g-C₃N₄.At low calcination temperature,a-Ni₂P₂O₇ nanoparticles are uniformly distributed on surface of g-C₃N₄,results in enhancing the harvesting ability of the composite.Furthermore,the formed staggered type II structure can promote the separation and transportion of photogenerated charge carriers and inhibit their recombination,thus boosts the activity of photocatalytic H₂ generation.In addition,compared with the crystalline Ni₂P₂O₇ modified g-C₃N₄,a-Ni₂P₂O₇/g-C₃N₄ shows smaller particle sizes and more negative conduction band position,resulting in excellent water splitting performance.The study on the preparation and performance of semimetal Bi decorated BiVO₄ for photoelectrochemical water splitting:Bi nanoparticles are successfully deposited on the surface of BiVO₄ by a facile synthesis method using TA and NaBH₄ as dispersants and reducing agents,respectively,which forms a heterostructure that benefical to the carriers’transportation.Photo-electrochemical analysis shows that Bi/BiVO₄ displays an excellent PEC water oxidation performance with respect to BiVO₄,which may results from the promoted electron-hole pairs’separation,the enhanced bulk separation efficiency and surface hole injection efficiency.In addition,Bi nanoparticles suppresses back reaction and plays a positive role for PEC water oxidation.