Reinforced stepwise dissociation of water molecules via U 5f-O 2p-Ti 3d gradient orbital coupling for photoelectrochemical water splitting

Actinide (An)-based materials have shown fascinating electronic and bonding properties related to f orbitals, demonstrating significant potential in catalysis. However, the catalytic utility of uranium is constrained by its low electron affinity and high reduction potential. In this study, we designed an asymmetric f-p-d gradient orbital coupling strategy through spatial engineering of the hybridization among U 5f, O 2p, and Ti 3d orbitals on TiO 2 nanorod arrays (U/TiO 2 NRA). This asymmetric 5f-2p-3d structure modulates the band structure to improve light absorption capacity and prolong the lifetime of charge carriers, while optimizing the adsorption energetics of reaction intermediates, thus enabling efficient stepwise water dissociation. The fabricated photoanode achieves a noteworthy photocurrent density and excellent operational stability, outperforming most reported TiO 2 -based catalysts. Through theoretical analyses, it is verified that the 5f buffer band at the asymmetric U−O−Ti sites, mediated by 5f-2p-3d gradient orbital coupling, facilitates electron transfer, which effectively promotes the adsorption, activation, and stepwise dissociation of water molecules at the dual atomic sites. In this work, a new design paradigm is established for the development of high-performance An-based catalytic materials.