Photocatalytic Carbon Dioxide Methanation by High-Entropy Oxides: Significance of Work Function

Abstract: Methane (CH4) formation from photocatalytic carbon dioxide (CO2) conversion in water is currently of interest because methane is a fuel, and it can also be transformed into other useful hydrocarbons. However, achieving high selectivity to produce methane remains a challenge because of the large number of contributing electrons (eight) in methanation. High-entropy oxides present a new pathway to tune the catalyst selectivity by arranging various cations in the lattice. This study aims to clarify the selectivity for methane formation in high-entropy photocatalysts containing hybrid d0 + d10 orbital configuration. Several oxides are designed and synthesized which have a base of 3-4 cations with d0 orbital configuration (titanium and zirconium with a valence of 4, and niobium and tantalum with a valence of 5) and incorporate 1-2 elements with d10 orbital configuration (zinc, gallium, indium, bismuth and copper). Results demonstrate that adding elements with a d10 electronic configuration is effective for methane formation, while the selectivity toward methanation is enhanced by increasing the work function of the d10 cations. Selectivity levels over 50% are achieved using these oxides, suggesting a potential strategy for designing new catalysts for methanation.