Electrochromic solar water splitting using a cathodic WO3 electrocatalyst

Solar-driven water splitting is an emerging technology with high potential to generate fuel cleanly and sustainably. In this work, we show that WO3 can be used as a cathodic electrocatalyst in combination with (Ag,Cu)InGaSe2 solar cell modules to produce hydrogen and provide electrochromic functionality to water splitting devices. This electrochromic effect can be used to monitor the charge state or performance of the catalyst for process control or for controlling the temperature and absorbed heat due to tunable optical modulation of the electrocatalyst. WO3 films coated on Ni foam, using a wide range of different sputtering conditions, were investigated as cathodic electrocatalysts for the water splitting reaction. The solar-to-hydrogen (STH) efficiency of solar-driven water electrolysis was extracted using (Ag,Cu)InGaSe2 solar cell modules with a cell band gap varied in between 1.15 and 1.25 eV with WO3 on Ni foam-based electrolyzers and yielded up to 13% STH efficiency. Electrochromic properties during water electrolysis were characterized for the WO3 films on transparent substrate (indium tin oxide). Transmittance varied between 10% and 78% and the coloration efficiency at a wavelength of 528 nm and the overpotential of 400 mV was 40 cm2 C−1. Hydrogen ion consumption in ion intercalation for electrochromic and hydrogen gas production for water electrolysis processes was discussed. [Display omitted] •An electrochromic hydrogen evolution reaction (HER) catalyst is reported.•The electrochromic effect can be used to monitor the charge state.•Solar-to-hydrogen (STH) efficiency of 13% is shown using Ag-CIGS, Ni-foam and WO3.•Transmittance varied between 10% and 78% during the different charge states of WO3.•Current consumed by the coloration and the HER processes are analyzed and discussed.