d¹⁰ Metal s-Orbital-Derived Conduction Band Enables Efficient Charge Separation in LiIn₂SbO₆: A Combined Band Structure and Molecular Orbital Analysis

Developing efficient photocatalysts for overall water splitting remains a key challenge in solar energy conversion, mainly due to limitations in charge separation and band alignment. Here, we propose a methodological framework that combines band theory with molecular orbital theory to move beyond conventional descriptors limited to band edge positions or crystal structure. This approach enables the rapid discovery and design of photocatalysts with efficient bulk charge transport and separation pathways through orbital composition, orientation, and bonding analysis. Using LiIn2SbO6 as a case study, density functional theory calculations reveal its conduction band minimum (CBM) originates from antibonding interactions between In/Sb 5s and O 2s orbitals, while the valence band maximum (VBM) consists mainly of O 2p nonbonding orbitals. This unique frontier orbital composition and orientation lead to spatially separated electron and hole transport pathways, facilitating bulk charge carrier separation via a one-dimensional covalent network of [In2O10] and [SbO6] units. Then, LiIn2SbO6 was synthesized via solid-state reaction and shows a UV absorption edge ∼3.99 eV. Although the pristine sample is photocatalytically inactive, loading with Pt cocatalyst effectively activates its performance, enabling overall water splitting under UV light with H2 and O2 generation rates of 13.7(2) and 6.8(1) μmol/h, respectively, and an apparent quantum yield of 1.84% at 254 nm. This confirms its superior bulk charge carrier separation efficiency. This work highlights the promise of d10 metal s-orbital-derived CBM for enhancing charge transport and provides a framework for discovering efficient photocatalysts through electronic structure and bonding analyses.