Abstract
This work studies the factors that affect the efficiency of the photoelectrochemical hydrogen evolution reaction (HER) using MoSx/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 MoSx nanofilms as a precursor for MoOz(S) nanofilms, which enhance the efficiency of the photo-activated oxygen evolution reaction (OER) using the MoOz(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 MoSx 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 MoSx/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 MoS4.5 films containing the highest concentration of catalytically active sites attributed to S ligands. During the anodic posttreatment of porous MoSx nanofilms, MoOz(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 MoOz(S)/WO3/FTO photoanodes that were prepared by posttreatment of the MoSx~3.2 precursor. The MoOz(S) film contributed to the effective photogeneration of electron–hole pairs that was followed by the transport of photoelectrons from MoOz(S) into the WO3 film and the effective participation of holes possessing strong oxidation ability in the OER on the surface of the MoOz(S) film.
Highlights
Obtaining and studying new nanomaterials for the formation of hybrid- and hetero-structures that provide effective splitting of water to produce hydrogen and oxygen is a principal task of alternative energy [1,2,3]
This work studies the factors that affect the efficiency of the photoelectrochemical hydrogen evolution reaction (HER) using MoSx/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 MoSx nanofilms as a precursor for MoOz(S) nanofilms, which enhance the efficiency of the photo-activated oxygen evolution reaction (OER) using the MoOz(S)/WO3/FTO heterostructures
Summary
Obtaining and studying new nanomaterials for the formation of hybrid- and hetero-structures that provide effective splitting of water to produce hydrogen and oxygen is a principal task of alternative energy [1,2,3]. Variation/optimization of the PLD conditions makes it possible to obtain metal oxide photoanodes for photoelectrochemical water splitting with enhanced functional characteristics [15,16,17] The use of this material to activate the hydrogen evolution reaction (HER) is constrained by the complexity of the formation of a specific structural and chemical state in WO3, which has high catalytic activity [18,19]. This work shows that the layered heterostructure created by the RPLD technique on an FTO-coated glass substrate and containing MoSx and WO3 nanostructured films can be used to create semiconductor photocathodes and photoanodes (after electrochemical posttreatment), which ensure efficient splitting of water under solar light Such a structure is formed through a relatively simple method in one chamber and using one technique. Qualitative photocatalytic characteristics of the heterostructure are achieved by controlling the ablation modes of the targets and by implementing optimal conditions for the deposition of a laser plume in an O- and S-containing reaction medium
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