Modulating water of crystallization on tungsten oxide photocatalyst to realize hydrogen production

<h2>Summary</h2> Regulating the electronic structures of a semiconductor is crucial for its photoelectric properties, but it is challenging. Herein, taking tungsten oxide (WO₃) as an example, which is capable of water oxidation but cannot realize hydrogen production due to its intrinsic electronic structures, we report that modulating the water of crystallization within WO₃ significantly affects its band structures, and continuous photocatalytic H₂ production on WO₃ can be realized. Reversible structural evolution between WO₃ hydrates (WO₃·xH₂O) and WO₃ demonstrates that introducing the water of crystallization enables the engineering of the crystalline and electronic structures. Theoretical calculation indicates that the water of crystallization disrupts the specific W–O bonds in the [WO₆] unit, which induces controllable lattice distortion with the dipole moment, enabling precise manipulation of the electronic structure and improvement of the charge transfer. This work provides insights into modulating microstructures through water of crystallization engineering for heterogeneous photocatalysis.