EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Design of active and selective co-catalysts constitutes one of the major challenges in developing heterogeneous photocatalysts for energy conversion applications. This work provides a comprehensive insight into thermally induced bottom-up generation and transformation of a series of promising Cu-based co-catalysts. We demonstrate that the volcano-type HER profile as a function of calcination temperature is independent of the type of the Cu precursor but can be linked to the change in state and location of the copper species. Supported by DFT modeling, a combined assessment using Raman spectroscopy, FTIR, DRS, HRTEM, XRD, XPS, UPS and TXRF, our data suggest that low temperature (< 200 °C) treatments facilitate optimal electronic communication of the Cu species to the TiO2, which allows for a more efficient charge utilization and yields maximum HER rates. In contrast, higher temperatures (> 200 °C) do not affect Cu oxidation state further but facilitate gradual, temperature-dependent surface-to-bulk diffusion of Cu, which results in stabilization as interstitial, tetracoordinated Cu+1 species. The disappearance of Cu from the surface and the introduction of new defect states marks the drop in HER performance. This work examines the variety of electronic and structural effects that are in control of photocatalytic activity of similar co-catalyst loaded semiconductor photocatalysts and will thus be relevant to the development of other advanced photocatalysts.