A Novel Two-dimensional Material PdSeO₃ For Water Electrolysis And Crystalline Mesoporous Silicon Photolysis Of Water For Hydrogen Evolution

How to use solar energy and electric energy to transform into clean and pollution-free hydrogen and oxygen has always been the pursuit of scientific researchers.Among them,semiconductor materials have always been an important research object in the energy conversion process of photocatalysis,electrocatalysis and photocatalysis.How to modify the existing catalysts with higher efficiency,explore new catalysts and develop catalysts with low cost and rich resources are the important research directions in the frontier hydrogen production.Hydrolysis in acidic environments offers higher energy efficiency,more compact battery design,higher gas purity,and less sensitivity to environmental impurities than alkaline hydrolysis.Two-dimensional nanomaterials are a hot research field in catalytic materials.Their unique structure greatly reduces the electron transport distance from the material to the surface,thus inhibiting the electron-hole recombination and improving the efficiency of surface redox reaction.In this paper,we have improved the synthetic methods of known two-dimensional materials?-and?-Pd Se O₃,and prepared nanosheets from bulk materials using an ultrasound-assisted liquid-phase stripping method prepared by graphene-like nanosheets.In acidic aqueous solution,0.2 M Na₂SO₄ aqueous solution and non-aqueous solution,the band gap,the maximum value of valence band and the minimum value of conduction band were determined by Mott-Schottky curve and linear potential scanning.Their transient photocurrent characteristics and electrochemical impedance spectra were studied.The bulk material is stable for at least 48 hours in aqueous solution with p H of 0-14.?-and?-Pd Se O₃nanosheets showed moderate catalytic activity for hydrogen evolution with overpotential of 185 m V and 209 m V,respectively,in 0.5 M sulfuric acid,which was much higher than that of the bulk materials.In addition,?-Pd Se O₃ bulk and nanosheet materials in 0.5 M sulfuric acid show good and similar OER catalytic activity(?10=381m V,405 m V),which enriches the original few types of acidic OER electrocatalysts.All above catalysts showed long-term stability.Therefore,?-Pd Se O₃ nanosheets are a good hydrolytic catalyst in acidic solution,and this kind of acidic hydrolytic catalyst for Pd based compounds is very rare.On the contrary,?-phase Pd Se O₃ with different structure does not exhibit OER catalytic performance.In addition,semiconductor Si,one of the most promising materials for solar photocatalytic hydrogen evolution,is also studied in this paper.Si is not only abundant but also has a unique narrow band gap that can capture light across a wide range of wavelengths in the solar spectrum.However,the difference between the conductive band edge of semiconductor silicon and the reduction potential of water is small,which is not enough to provide a large photocatalytic driving force.Moreover,surface oxidation is easy to occur in aqueous solution,which all limit the application of silicon materials in photocatalytic hydrogen evolution reaction.In this paper,crystalline mesoporous silicon was prepared by annealing in argon atmosphere with trichlorosilane as silicon source,magnesium silicate as carrier and the in-situ produced salt by-product as template by improving the synthetic method.The preparation method widens the band gap of silicon material and improves the reaction driving force.The specific surface area of silicon material is increased to increase the contact area with the solution.This method can also improve the crystallinity of silicon materials and reduce material defects,thus reducing the recombination of photogenerated carriers and improving the photocatalytic reaction efficiency of silicon materials.The width of the band gap,the position of the top of the valence band and the bottom of the conduction band of the material were determined based on UV-Vis diffuse reflectance spectroscopy and UV photoelectron spectroscopy.The investigations results show that the crystal mesoporous silicon material heated for 40 min in 700°C argon has the best visible-light absorption and the photocatalytic rate of hydrogen production per unit time can reach 2719?mol·h^-1·g^-1 in 5 hours using triethanolamine as sacrificial agent.After a series of characterization of the photocatalytic reaction of the sample,it was found that the morphology,phase state and composition of the sample did not change significantly,except for the partial surface oxidation,the sample still maintained a high stability.Therefore,this crystalline mesoporous silicon material has outstanding application prospects in the area of photocatalytic hydrogen evolution.