Visible-Light-Responsive Oxyhalide PbBiO₂Cl Photoelectrode: On-Site Flux Synthesis on a Fluorine-Doped Tin Oxide...

The performance of photoelectrodes is hugely affected by the preparation method. Although a flux synthesis is useful to endow semiconductor particles with the desired properties such as high crystallinity, there are only a few reports on its application to photoelectrode fabrication, probably because relatively high temperatures are necessary. In the present study, we introduce a new concept for on-site flux synthesis of semiconductor crystals on a commonly used fluorine-doped tin oxide (FTO) substrate; a seed layer is predeposited and then treated with an appropriate flux containing other required elements at a right temperature lower than the limit temperature of FTO but sufficiently high to transform the seed layer to the target material with the aid of flux. Here, an oxyhalide PbBiO₂Cl, one of the promising semiconductors for achieving visible-light water splitting, is selected as a target material. Combination of a BiOCl seed layer and the NaCl-PbCl₂ flux containing other precursors enables the seed layer to transform into PbBiO₂Cl crystals even at 450 °C. The thickness of the PbBiO₂Cl layer can be controlled by changing the thickness of the BiOCl seed layer for efficient photon-to-current conversion. Owing to a good contact at the semiconductor-substrate interfaces as well as the high quality of PbBiO₂Cl crystals, the flux-synthesized PbBiO₂Cl photoelectrode shows a significantly improved PEC performance compared with those prepared from the particulate PbBiO₂Cl samples via the conventional squeegee method. In addition, the present PbBiO₂Cl photoelectrodes exhibit both anodic and cathodic photoresponses with substantially high current values depending on the applied potentials; the unusual phenomenon is affected by the conditions in flux-assisted synthesis. The present study provides a new and effective way for fabricating efficient photoelectrodes of various semiconductors on various substrates and a possible option to control their morphologies and p/n types for further improvement in performance.