Single-cluster Functionalized TiO₂ Nanotube Array for Boosting Water Oxidation and CO₂ Photoreduction to CH₃OH

Solar-driven CO₂ reduction and water oxidation to liquid fuels represents a promising solution to alleviate energy crisis and climate issue, but it remains a great challenge for generating CH₃OH and CH₃CH₂OH dominated by multi-electron transfer. Single-cluster catalysts with super electron acceptance, accurate molecular structure, customizable electronic structure and multiple adsorption sites, have led to greater potential in catalyzing various challenging reactions. However, accurately controlling the number and arrangement of clusters on functional supports still faces great challenge. Herein, we develop a facile electrosynthesis method to uniformly disperse Wells-Dawson- and Keggin-type polyoxometalates on TiO₂ nanotube arrays, resulting in a series of single-cluster functionalized catalysts P₂M₁₈O₆₂@TiO₂ and PM₁₂O₄₀@TiO₂ (M=Mo or W). The single polyoxometalate cluster can be distinctly identified and serves as electronic sponge to accept electrons from excited TiO₂ for enhancing surface-hole concentration and promote water oxidation. Among these samples, P₂Mo₁₈O₆₂@TiO₂-1 exhibits the highest electron consumption rate of 1260 μmol g^-1 for CO₂-to-CH₃OH conversion with H₂O as the electron source, which is 11 times higher than that of isolated TiO₂ nanotube arrays. This work supplied a simple synthesis method to realize the single-dispersion of molecular cluster to enrich surface-reaching holes on TiO₂, thereby facilitating water oxidation and CO₂ reduction.