Active high-entropy photocatalyst designed by incorporating alkali metals to achieve d0+d10+s0 cationic configurations and wide electronegativity mismatch

Abstract: Photocatalytic hydrogen (H2) production and carbon dioxide (CO2) conversion to methane (CH4) are considered promising solutions for reducing CO2 emissions. However, the development of highly active photocatalysts is essential to efficiently drive these reactions without harming the environment. In this study, we introduce a strategy that incorporates elements with both low and high electronegativities into catalysts based on transition metals, thereby enhancing both reactant adsorption and charge transfer. This strategy is implemented in a high-entropy oxide (HEO) by adding cesium, an alkali metal with very low electronegativity, and gallium, a metal with high electronegativity, to transition metals titanium, niobium and tantalum. The resulting oxide, TiNbTaGaCsO9 with a large concentration of oxygen vacancies, exhibits strong light absorption, a low bandgap and a suitable band structure for both hydrogen evolution and CO2 conversion. Compared to HEOs with only d0 or d0+d10 cationic configurations, the synthesized oxide with a wide electronegativity difference and mixed d0+d10+s0 cationic configurations shows significantly higher activity for both H2 and CH4 production, even without using a cocatalyst. These results demonstrate a design strategy for creating highly active HEOs containing alkali metals by taking advantage of the electronegativity mismatch across the periodic table.