Strongly enhanced visible light photoelectrocatalytic hydrogen evolution reaction in an n-doped MoS2 /TiO2(B) heterojunction by selective decoration of platinum nanoparticles at the MoS2 edge sites

Abstract

Herein, we demonstrate strongly enhanced visible light photoelectrocatalytic hydrogen evolution reaction (HER) in few-layer MoS₂ grown on a mesoporous TiO₂(B) nanobelt (NB) by selective decoration of platinum (Pt) nanoparticles (NPs) on the edge/defect sites of the MoS₂ layer. Three catalytically active components are anchored together to increase the photoelectrocatalytic HER activity synergistically, beyond that of commercial Pt/C electrodes (20 wt% Pt). An extremely low concentration of Pt NPs (1.4 wt%) with average size ∼3.8 nm was decorated over the preferentially edge-site-exposed few-layer MoS₂, with lateral sizes 130–350 nm, as evidenced from high-angle annular dark-field STEM imaging. During the heterojunction formation, S is doped in the TiO₂ layer causing a high density of electrons in TiO₂ that migrate to the MoS₂ layer inducing n-type doping in it and thus TiO₂ acts as an efficient photocathode in photoelectrocatalysis. Quantitative XPS analysis reveals that the catalytically active bridging S₂²⁻/apical S²⁻ increases up to ∼72% after the formation of the ternary system Pt@MoS₂/TiO₂(B). S-enriched MoS₂/TiO₂(B) selectively loaded with Pt NPs on the edge sites of MoS₂ exhibits a giant enhancement in the HER activity in an acidic medium under light. We record a nearly 16 fold higher exchange current density (0.296 mA cm⁻²) for the ternary system as compared to that of the MoS₂/TiO₂ binary system under visible light excitation. The marginally Pt loaded ternary system exhibits an extremely low charge transfer resistance (14 Ω) and a low overpotential as well as Tafel slope (−74 mV and 30 mV dec⁻¹, respectively) boosting the overall HER performance under visible light. Chronopotentiometric measurements reveal the high stability of binary and ternary systems to sustain a 10 mA cm⁻² cathodic current up to 12 hours. The results show that the marginally loaded Pt NPs activate the inert basal plane, edge sites of MoS₂ and porous sites of TiO₂, forming an integrated network where the photogenerated electrons can easily be injected from the TiO₂ to MoS₂ and then to Pt NPs, presenting a feasible approach to boost the HER activity under visible light.