Theoretical Study On Improving Hydrogen Production By TiO₂?B? Photolysis

The use of photocatalytic technologies for harvesting and converting sunlight into chemical energy carriers that can be stored?e.g.,hydrogen?is a promising and rapidly developing research topic.In principle,a suitable band gap and appropriate band edge positions are prerequisites for a photocatalyst with a sufficiently high redox capability to catalyze water-splitting.Moreover,high transfer coefficient and fast charge carrier separation are important factors.Differences in orbital characteristics and carrier mobility at the conduction band minimum?CBM?and valance band maximum?VBM?are highly beneficial to prevent electron-hole pair recombination,thus elongating the carrier lifetimes.Since Fujisima and Honda1 first reported their water-splitting system,hundreds of new materials have been demonstrated to exhibit photocatalytic activity for water splitting.However,the ability of these materials to absorb and convert sunlight is still below the required 10% photoelectric transformation efficiency because of a wide band gap and/or misaligned band edge positions.Although TiO₂ is considered the most promising candidate for commercial photocatalysts,its wide band gap is still a serious problem leading to low quantum efficiency under visible-light,hindering commercial and industrial applications.It was found that the doping of TiO₂ could reduce the band gap and increase the response range of TiO₂ to visible light.Adding dopants to prevent or slow the recombination of photogenerated electron-hole pairs,improve photon quantum efficiency,and improve the stability of photocatalytic materials.In this paper,the metastable monoclinic polycrystalline TiO₂?B?in the TiO₂ family is selected and the study is based on the first-principles calculation and the high-throughput method of cluster expansion?CE?.In this study,a high-throughput approach based on combining first principles calculations with the cluster expansion?CE?formalism was employed to determine which element?s?among the selected RMs can be doped into TiO₂?B?,to gauge the extent to which the dopant?s?can replace Ti atoms,and to investigate the possibility of generating new ordered structures.Monte Carlo?MC?simulations were used to study the thermodynamic stability of the promising phase?s?within the bronze prototype.The electronic structures and optical absorption of the stable phase?s?were calculated using an accurate HSE06 method to evaluate the photoelectrochemical activity.Ten representative metals?RMs?were systematically explored via first principles calculations and CE prediction,including precious metals?Pt and Pd?,normal transition metals?V,Mn,Mo,and Ru?,d0 elements?Nb and Zr?,and d10 elements?Ge and Sn?with +4 valences and similar ionic radii to Ti4+.Interestingly,our calculations reveal that Pt and Ge can be doped into TiO₂?B?to generate ordered phases,whereas the other eight metals likely cannot be doped into TiO₂?B?.Moreover,the new predicted thermodynamically stable TiPtO4 exhibits a favorable band gap and reasonable band edge positions for water splitting,thereby showing great potential as an outstanding photocatalyst for solar energy conversion.