The influence of water-induced crystallization on the photoelectrochemical properties of porous anodic tin oxide films

CdS-Decorated Porous Anodic SnOx Photoanodes with Enhanced Performance under Visible Light

Electrochemically generated nanoporous tin oxide films have already been studied as photoanodes in photoelectrochemical water splitting systems. However, up to now, the most significant drawback of such materials was their relatively wide band gap (ca. 3.0 eV), which limits their effective performance in the UV light range. Therefore, here, we present for the first time an effective strategy for sensitization of porous anodic SnO_x films with another narrow band gap semiconductor. Nanoporous tin oxide layers were obtained by simple one-step anodic oxidation of metallic Sn in 1 M NaOH followed by further surface decoration with CdS by the successive ionic layer adsorption and reaction (SILAR) method. It was found that the nanoporous morphology of as-anodized SnO_x is still preserved after CdS deposition. Such SnO_x/CdS photoanodes exhibited enhanced photoelectrochemical activity in the visible range compared to unmodified SnO_x. However, the thermal treatment at 200 °C before the SILAR process was found to be a key factor responsible for the optimal photoresponse of the material.

Tuning the Photoelectrochemical Properties of Narrow Band Gap Nanoporous Anodic SnOx Films by Simple Soaking in Water

Nanoporous tin oxide layers obtained via anodic oxidation of metallic tin at the potential of 4 V in the alkaline electrolyte (1 M NaOH) were soaked in distilled water for various durations (from 2 h to 120 h) to verify the influence of water-enabled crystallization on the morphology, composition, and related optical and photoelectrochemical properties of such kind of anodic SnO_x. Although water soaking generally contributes to more stoichiometric and crystalline tin oxide, it was confirmed that at the initial stages of the water-induced dissolution-redeposition process, material exhibits enhanced photoelectrochemical performance under simulated sunlight irradiation. However, long-time exposure to water results in a gradual widening of the material's band gap, shifting of the photoelectrochemical spectra towards higher energies, and almost complete deterioration of the photoelectrochemical activity under sunlight irradiation.