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

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, were decorated over the preferentially edge-site-exposed few-layer MoS₂, with lateral sizes 130-350 nm, as evidenced from the high-angle annular dark-field STEM imaging. During the heterojunction formation, S is doped in the TiO₂ layer causing the 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 the 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 the light. We record nearly 16 fold higher exchange current density (0.296 mA/cm²) for the ternary system as compared to the MoS₂/TiO₂ binary system under visible light excitation. The marginal Pt loaded ternary system exhibits an extremely low charge transfer resistance (14) and low overpotential as well as Tafel slope (-74 mV and 30 mV dec^-1, respectively) boosting the overall HER performance under the visible light. Chronopotentiometric measurements reveal the high stability of binary and ternary system to sustain a 10 mA/cm² cathodic current up to 12 hours. The results show that the marginallyloaded Pt NPs activate the inert basal plane, edge sites of MoS₂ and porous sites of TiO₂, making 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.