Positive Impact of Weak Hydrogen Bonds on O–H Bond Dissociation in Photocatalytic Water Splitting

In photodriven catalytic water splitting for hydrogen production, much focus is placed on photocatalyst design and bandgap engineering, while the role of water molecule configurational changes in enhancing interfacial catalytic rates is often overlooked. This study investigates the impact of water molecule configurations on SrTiO₃ photocatalysts, using a hydrogel matrix that creates a distinct hydrogen-bonding environment for water. The weakly hydrogen-bonded intermediate water in the hydrogel is more easily released as small clusters upon photoactivation, boosting the interfacial catalytic reaction rate. In situ Raman spectroscopy reveals dynamic changes in hydrogen-bonding patterns during photoactivation, with the intermediate water state playing a key role in the catalytic reaction. Molecular dynamics simulations show that thermal effects activate O-H bonds, enhancing the diffusion of active water molecules toward the catalytic layer and improving water splitting. Experimental results and density functional theory (DFT) calculations indicate that the hydrogel reduces the level of hydrogen bonding between adjacent water molecules and lowers the O-H bond dissociation energy, decreasing the reaction energy barrier on the catalyst surface. In the saturated hydrogel system, without thermal effects, a hydrogen evolution rate of 215.62 mmol m^-2 h^-1 and an oxygen evolution rate of 105.95 mmol m^-2 h^-1 are achieved under simulated sunlight illumination, yielding a solar-to-hydrogen (STH) efficiency of 1.43%. Under the influence of the photothermal effect, the STH efficiency was further enhanced to 1.85%. The hydrogen production rate is 3.85 times higher than that of bulk water.