Water adsorption at the (010) and (101) surfaces of CuWO4

Copper tungstate (CuWO₄) has attracted significant attention over the past two decades due to its performance as an electro-photocatalyst for water splitting, with many studies focusing on its structural, electronic, and the redox properties. However, the adsorption of water onto CuWO₄, which plays a critical role in the photocatalytic water splitting process, has not been investigated in detail. In this study, we have employed density functional theory (DFT) calculations to investigate water adsorption onto the CuWO₄ pristine (010) and reduced (101) surfaces. The charge transfer for each mode of adsorption was calculated after optimization. Adsorption of multiple water molecules was simulated based on the single water adsorption system. We have calculated the electronic properties, Bader atomic charges, adsorption energies, surface free energies, work functions, and band gaps at each coverage of H₂O on both surfaces. The surface phase diagrams as a function of the temperature and partial pressure of H₂O were also configured to determine water coverage under particular environmental conditions. Our study provides a comprehensive understanding of the adsorption of water on the major CuWO₄ surfaces, which is an important preliminary step in our investigation of photocatalytic water splitting over CuWO₄.