Photoelectrochemical activity of the nanostructured electrodes based on the SnO2/SnS2 – Heterojunction type II vs S-scheme mechanism

In photoelectrochemical cells (PECs), the water-splitting process requires a directed electron flow. Therefore, the interface structure between the photoelectrode components is crucial for its photoelectrochemical activity. In the presented work, we performed studies to determine the effect of the heterojunctions formed between the applied photocatalysts (SnO2/SnS2) and the substrate/photocatalyst. To this end, we prepared electrodes on three different substrates (ITO, Ti etched, and Ti covered with TiOx) composed of SnS2, SnO2, and SnO2/SnS2 flower-like (3D-2D) structures. The layers were obtained via the chemical bath deposition method. The results revealed that depending on the applied substrate, the formed intermediate phases may block (In2S3) or support (TinO2n-1) the electron transfer via the substrate/photocatalyst interface. Among all samples, the SnO2/SnS2-based electrode obtained on Ti/TiOx substrate showed the best photoelectrochemical performance due to the formed type I (substrate/SnO2) and S-scheme (SnO2/SnS2) heterojunctions. This work demonstrates the effect of photoelectrode structure on its electrochemical activity. Based on the analysis of the (micro)structural, surface, optical, and photoelectrochemical properties, we have proposed: (1) the substrate/photocatalyst interface structures, (2) a band diagram with charge transfer mechanism, and (3) the growth mechanism of the nanostructured layers, explaining the formation of surface defects.