This work studies the factors that affect the efficiency of the photoelectrochemical hydrogen evolution reaction (HER) using MoS_x/WO₃ 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)/WO₃/FTO heterostructures. The nanocrystalline WO₃ 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 H₂S gas of varied pressure at room temperature of the substrate. Studies of the energy band structures showed that for all MoS_x/WO₃/FTO samples, photo-activated HER in an acid solution proceeded through the Z-scheme. The highest photoelectrochemical HER efficiency (a photocurrent density ~1 mA/cm² at a potential of ~0 V under Xe lamp illumination (~100 mW/cm²)) 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/cm² at 1.6 V) was detected for MoO_z(S)/WO₃/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 WO₃ film and the effective participation of holes possessing strong oxidation ability in the OER on the surface of the MoO_z(S) film.

We studied the possibility of using pulsed laser deposition (PLD) for the formation of a MoS_x/WSe2 heterostructure on a dielectric substrate. The heterostructure can be employed for effective solar water splitting to produce hydrogen. The sapphire substrate with the conducting C(B) film (rear contact) helped increase the formation temperature of the WSe₂ film to obtain the film consisting of 2H-WSe₂ near-perfect nanocrystals. The WSe₂ film was obtained by off-axis PLD in Ar gas. The laser plume from a WSe₂ target was directed along the substrate surface. The preferential scattering of selenium on Ar molecules contributed to the effective saturation of the WSe₂ film with chalcogen. Nano-structural WSe₂ film were coated by reactive PLD with a nanofilm of catalytically active amorphous MoS_x~4. It was established that the mutual arrangement of energy bands in the WSe₂ and MoS_x~4 films facilitated the separation of electrons and holes at the interface and electrons moved to the catalytically active MoS_x~4. The current density during light-assisted hydrogen evolution was above ~3 mA/cm² (at zero potential), whilst the onset potential reached 400 mV under irradiation with an intensity of 100 mW/cm² in an acidic solution. Factors that may affect the HER performance of MoS_x~4/WSe₂/C(В) structure are discussed.

Pulsed laser ablation of MoS₂ and WO₃ targets at appropriate pressures of background gas (Ar, air) were used for the preparation of new hybrid nanostructured catalytic films for hydrogen production in an acid solution. The films consisted of a nanostructured WO_3−y underlayer that was covered with composite MoS₃/np-Mo nanocatalyst. The use of dry air with pressures of 40 and 80 Pa allowed the formation of porous WO_3−y films with cauliflower- and web-like morphology, respectively. The ablation of the MoS₂ target in Ar gas at a pressure of 16 Pa resulted in the formation of amorphous MoS₃ films and spherical Mo nanoparticles. The hybrid MoS₃/np-Mo//WO_3−y films deposited on transparent conducting substrates possessed the enhanced (photo)electrocatalytic performance in comparison with that of any pristine one (MoS₃/np-Mo or WO_3−y films) with the same loading. Modeling by the kinetic Monte Carlo method indicated that the change in morphology of the deposited WO_3−y films could be caused by the transition of ballistic deposition to diffusion limited aggregation of structural units (atoms/clusters) under background gas pressure growth. The factors and mechanisms contributing to the enhancement of the electrocatalytic activity of hybrid nanostructured films and facilitating the effective photo-activation of hydrogen evolution in these films are considered.

Pulsed laser deposition of nanostructured molybdenum sulfide films creates specific nonequilibrium growth conditions, which improve the electrocatalytic properties of the films in a hydrogen evolution reaction (HER). The enhanced catalytic performance of the amorphous a-MoS_x (2 ≤ x ≤ 3) matrix is due to the synergistic effect of the Mo nanoparticles (Mo-NP) formed during the laser ablation of a MoS₂ target. This work looks at the possibility of employing a-MoS_x/NP-Mo films (4 and 20 nm thickness) to produce hydrogen by photo-stimulated HER using a p-Si cathode. A simple technique of pulsed laser p-Si doping with phosphorus was used to form an n⁺p-junction. Investigations of the energy band arrangement at the interface between a-MoS_x/NP-Mo and n⁺-Si showed that the photo-HER on an a-MoS_x/NP-Mo//n⁺p-Si photocathode with a 20 nm thick catalytic film proceeded according to a Z-scheme. The thickness of interfacial SiO_y(P) nanolayer varied little in photo-HER without interfering with the effective electric current across the interface. The a-MoS_x/NP-Mo//n⁺p-Si photocathode showed good long-term durability; its onset potential was 390 mV and photocurrent density was at 0 V was 28.7 mA/cm². The a-MoS_x/NP-Mo//n⁺p-Si photocathodes and their laser-based production technique offer a promising pathway toward sustainable solar hydrogen production.

The thermochemical treatment of tungsten trioxide (WO₃) nanostructured films in hydrogen sulfide to obtain tungsten disulfide (WS₂) layers in the WS₂/WO₃ hybrid structure is studied. The temperature and treatment time influence the structural-phase state, morphology, optical properties of a WS₂/WO₃/FTO photocathode (on fluorinated tin oxide (FTO) substrates), and its photoelectrocatalytic activity in the hydrogen evolution reaction in acidic solution is established. The sulfidation of WO₃ nanoneedle films leads to the formation of a WS₂/WO₃ nanocrystalline hybrid structure under optimal conditions, which provides the separation of photogenerated carriers (electrons and holes) at the interphase boundaries (heterojunctions) necessary for the efficient photoactivated hydrogen evolution reaction according to Z scheme. The calculations of thermodynamic properties of the WS₂/WO₃ hybrid nanocatalyst show that synergistic effect of nanophases is possible in it to increase the catalytic activity of hydrogen evolution both on the basal planes of WS₂ nanoclusters and on the surface of metal oxide nanoclusters.

The influence of the chemical state of a WO_y thin-film precursor on formation of WSe₂ nanofilms under rapid selenization on a glassy carbon substrate at 900°C is studied. A nanolayer of amorphous molybdenum sulfide (MoS_{x ~ 3}), which has high catalytic activity in the electrochemical reaction of hydrogen evolution, is applied onto the surface of the obtained WSe₂ films by pulsed laser deposition. It is shown that the composition of the WO_y thin-film precursor has a significant effect on the morphology of the WSe₂ nanolayers, and this characteristic largely determines the efficiency of hydrogen evolution by the MoS₃/WSe₂ heterostructure upon photoactivated water splitting. The most efficient hydrogen evolution is found for the MoS₃/WSe₂ photocathode heterostructure containing WSe₂ in the form of crystal petals of ~50 nm in thickness, with these crystals oriented perpendicular to the substrate surface. A theoretical analysis of the possible effect of synergistic interaction at the MoS₃/WSe₂ interface on the efficiency of hydrogen evolution is carried out. Density functional theory calculations have shown that MoS₃ clusters can increase the efficiency of the hydrogen evolution reaction upon contact with surface regions of WSe₂ nanocrystals different in atomic packing.