Arc Synthesis, Crystal Structure, and Photoelectrochemistry of Copper(I) Tungstate.

A little-studied p-type ternary oxide semiconductor, copper(I) tungstate (CuWO), was assessed by a combined theoretical/experimental approach. A detailed computational study was performed to solve the long-standing debate on the space group of CuWO, which was determined to be triclinic 1. CuWO was synthesized by a time-efficient, arc-melting method, and the crystalline reddish particulate product showed broad-band absorption in the UV-visible spectral region, thermal stability up to ∼260 °C, and cathodic photoelectrochemical activity. Controlled thermal oxidation of copper from the Cu(I) to Cu(II) oxidation state showed that the crystal lattice could accommodate Cu cations up to ∼260 °C, beyond which the compound was converted to CuO and CuWO. This process was monitored by powder X-ray diffraction and X-ray photoelectron spectroscopy. The electronic band structure of CuWO was contrasted with that of the Cu(II) counterpart, CuWO using spin-polarized density functional theory (DFT). Finally, the compound CuWO was determined to have a high-lying (negative potential) conduction band edge underlining its promise for driving energetic photoredox reactions.