Hydrogen evolution/spillover effect of single cobalt atom on anatase TiO2 from first-principles calculations

In spite of progress, there is a long way to go in the use of non-precious metals instead of precious metals as catalysts in chemical reactions. Here we report an anatase TiO2-supported single-atom (SA) Co system for hydrogen evolution and also study its hydrogen spillover effect using first-principles calculations. Two stable forms of SA Co on the anatase TiO2(101) surface, achieved by adsorption and substitution, induce different confinement effects. The SA Co in the interstices of the surface exhibits better hydrogen evolution activity than bulk counterpart. The hydrogen evolution reaction proceeds on the partially hydrogenated surface of Co-1/TiO2, where SA Co and adjacent O are active sites. The substitution of Co for Ti promotes the formation of surface O vacancies and the reduction of Ti4+ to Ti3+ in the H-2 atmosphere, indicative of an enhanced hydrogen spillover effect. The possible catalytic mechanisms of SA catalysts in the two forms are proposed by the calculation of reaction kinetics. The present work highlights the complexity and diversity of the confinement effect of transition metal SA in oxides, and broadens their applications in catalysis and of defect engineering.