Hydrogen-Bond Network Drives Water Splitting by Neutral Tantalum Center

Abstract

Elucidating the water splitting by neutral metals is crucial for understanding the structure–reactivity relationship of catalysts. However, experimental characterization of such neutral metal–water systems remains extremely challenging due to the difficulty in mass selection. Herein, the reactions of neutral tantalum with water were studied by size-specific infrared-vacuum ultraviolet spectroscopy with the combination of quantum chemical calculations and ab initio molecular dynamics simulations. The agreement between experimental and theoretical results identifies the key products of stepwise solvated hydrides HTa(OH)3(H2O)n (n = 1–3). The n = 1 monohydrate is stabilized by a cyclic double hydrogen bond motif between the HTa(OH)3 core and the water molecule, while subsequent hydration (n = 2 and 3) progressively extends this hydrogen bond network to form the first solvation shell. Significantly, the first water molecule in TaO(H2O)n inhibits the water dissociation reaction on TaO, whereas the second water molecule in TaO(H2O)n is able to trigger the water splitting facilitated by a six-membered hydrogen bond network. This work provides the direct spectral evidence of intrinsic structure and solvation effect of hydrolysis products and offers a molecular-level prelude to the macroscopic mechanism of single-atom catalysts for water splitting.