Effect Of Ni Cocatalyst On Photocatalytic Hydrogen Evolution Reaction Of Anatase TiO₂ By First-principles Calculations

TiO₂ is a star photocatalyst for overall water splitting.Its low efficiency of hydrogen evolution reaction?HER?can be improved by loading proper cocatalysts.To get insight into the mechanism of experimental observations,we take Ni/TiO₂ photocatalytic system as a model and perform detailed first-principles calculations.Our results demonstrate that small Ni_n?n=1-4?clusters have stronger interactions with anatase TiO₂?001?than?101?surfaces according to the calculated adsorption energies.It is found that Nin cluster is more difficult to undergo aggregation on?001?surface than?101?surface.The structural difference of two surfaces determines the properties above.The adsorption of Nin cluster on TiO₂ surfaces benefits the separation of photogenerated charge by introducing mid-gap states into the band gap and elevates the Fermi level toward the conduction band,which is in favor of the occurrence of HER.Electrochemical computational method is used to investigate the mechanism of HER.Our results indicate that the active site of HER in Nin/TiO₂ systems is the O_2c atoms binding or near to Nin cluster.Loading Nin clusters remarkably reduces the Gibbs free energy of HER compared with the clean surfaces.Our work reveals the growth behavior of Ni cocatalyst on anatase TiO₂ surfaces and presents a reasonable explanation on the experimental enhancement of activity for photocatalytic HER after loading Ni cocatalysts.