Metallic Ni-Based Co-catalyst Materials:Preparation,Characterization And Photocatalytic Water Splitting For Hydrogen Evolution

Solar-driven semiconductor photocatalytic hydrogen production technology has brought hope to the current situation of the urgent need to find alternative energy sources in contemporary society.There are currently hundreds of semiconductors used in the field of photocatalytic hydrogen production,but the shortcoming of the inherent photogenerated electron-hole pair recombination rate of a single traditional semiconductor affects its photocatalytic efficiency and limits the application of semiconductor photocatalysts.Therefore,in order to achieve the design of solar-driven efficient photocatalytic materials for hydrogen evolution,improving the photo-generated electron-hole recombination efficiency is the first factor to be considered.Many previous studies have shown that coupling with co-catalyst can effectively inhibit photo-generated electron-hole recombination,while electrons are transferred to the co-catalyst,which is an effective method for modify low photocatalytic efficiency to single traditional semiconductors.In this work,metallic nickel-based phosphide is used as a photocatalytic electron co-catalyst,and it is coupling with traditional semiconductor graphite phase carbon nitride?g-C₃N₄?or metal oxide?Cu₂O?,which improves the efficiency of photo-generated carrier separation.At the same time,the inherent shortcomings of traditional semiconductors such as low specific surface area and oxidizability are also improved.The specific research contents are as follows:?1?Using nickel hydroxide?Ni?OH?₂?as the precursor,the HCN/Ni₅P₄ system was prepared by a simple electrostatic self-assembly and in-situ phosphating method.By controlling the mass ratio of Ni₅P₄,the photocatalytic hydrogen evolution rate of the composite under visible light was investigated.The morphology and structural characteristics of HCN/Ni₅P₄ samples were analyzed by SEM,TEM,XRD,UV-vis,XPS,BET,as well as DFT calculations.The PC and EIS experiments were used to analyze the separation and transmission efficiency of photo-generated carriers.The results have shown that during the photocatalytic reaction,electrons are transferred to the co-catalyst due to the presence of Ni₅P₄ with high electron density.The high work function of Ni₅P₄?5.23 eV?constructed schottky junctions when recombined with protonated carbon nitride?HCN?.The presence of schottky barriers further hindered the flow of photogenerated electrons back to protonated carbon nitride?HCN?.Secondly,the morphological analysis revealed that Ni₅P₄ has a porous flower-like structure,which also improved the shortcoming of low specific surface area of carbon nitride,provided more active sites for the photocatalytic hydrogen evolution reaction,and further improved the hydrogen evolution activity of the HCN/Ni₅P₄ photocatalytic composite,In addition,the energy transfer of the photocatalytic reaction is considered in detail,which is consistent with the photocatalytic mechanism.?2?Using nickel-iron layered double hydroxide?NiFe LDH?as the precursor,a simple in-situ phosphating method was used to obtained the Cu₂O/Ni_0.5Fe₂P photocatalyts.The morphology and structural characteristics of the samples were investigated by SEM,TEM,XRD,UV-vis,XPS and other characterization methods.The PC and EIS experiments were used to analyze the separation and transmission efficiency of photo-generated carriers.The results showed that the high conductivity of the metallic Ni_0.5Fe₂P allows photogenerated electrons to flow onto the co-catalyst,the photogenerated electron-holes are effectively separated,and the photocatalytic hydrogen evolution reaction performance is improved.Secondly,metallic Ni_0.5Fe₂P covered on the surface of Cu₂O and hindered the oxidation of cuprous oxide,In addition,the energy transfer of the photocatalytic reaction is considered in detail,which is consistent with the photocatalytic mechanism.