Performance and Mechanism of Photoelectrocatalytic Activity of MoS(x)/WO(3) Heterostructures Obtained by Reactive Pulsed Laser Deposition for Water Splitting

This work studies the factors that affect the efficiency of the photoelectrochemical hydrogen evolution reaction (HER) using MoS(x)/WO(3) nano-heterostructures obtained by reactive pulsed laser deposition (RPLD) on glass substrates covered with fluorinated tin oxide (FTO). Another focus of the research is the potential of MoS(x) nanofilms as a precursor for MoO(z)(S) nanofilms, which enhance the efficiency of the photo-activated oxygen evolution reaction (OER) using the MoO(z)(S)/WO(3)/FTO heterostructures. The nanocrystalline WO(3) film was created by laser ablation of a W target in dry air at a substrate temperature of 420 °C. Amorphous MoS(x) nanofilms (2 ≤ x ≤ 12) were obtained by laser ablation of an Mo target in H(2)S gas of varied pressure at room temperature of the substrate. Studies of the energy band structures showed that for all MoS(x)/WO(3)/FTO samples, photo-activated HER in an acid solution proceeded through the Z-scheme. The highest photoelectrochemical HER efficiency (a photocurrent density ~1 mA/cm(2) at a potential of ~0 V under Xe lamp illumination (~100 mW/cm(2))) was found for porous MoS(4.5) films containing the highest concentration of catalytically active sites attributed to S ligands. During the anodic posttreatment of porous MoS(x) nanofilms, MoO(z)(S) films with a narrow energy band gap were formed. The highest OER efficiency (a photocurrent density ~5.3 mA/cm(2) at 1.6 V) was detected for MoO(z)(S)/WO(3)/FTO photoanodes that were prepared by posttreatment of the MoS(x)(~3.2) precursor. The MoO(z)(S) film contributed to the effective photogeneration of electron–hole pairs that was followed by the transport of photoelectrons from MoO(z)(S) into the WO(3) film and the effective participation of holes possessing strong oxidation ability in the OER on the surface of the MoO(z)(S) film.