TiO₂ Nanorod Array Conformally Coated with\na Monolayer MoS₂ Film: An Efficient Electrocatalyst for\nHydrogen Evolution Reaction

Abstract

Heterostructures,\nparticularly the shell–core (2D@1D) nanostructure\nwith atomically thin layers of transition metal dichalcogenides, exhibit\nan excellent electrocatalytic hydrogen evolution reaction (HER) activity.\nHerein, we introduce a facile and precisely controlled synthesis of\na shell–core heterostructure that comprises TiO₂ nanorods (TNRs) as a core array conformally covered by a continuous\nmonolayer molybdenum disulfide (ML-MoS₂) film as a shell.\nThe TNR array was grown by a hydrothermal process, followed by the\nconformal coating of the ML-MoS₂ film via metal–organic\nchemical vapor deposition. Interestingly, the shell–core heterostructure\n(ML-MoS₂@TNRs) shows a significant enhancement in the HER\nactivity with an onset overpotential at 140 mV vs reversible hydrogen\nelectrode and a Tafel slope of ∼80 mV/dec. Based on our experimental\nresults together with first-principle calculations, we attribute the\nenhanced HER performance of ML-MoS₂@TNRs to the synergetic\neffect of the following characteristics. (i) A large number of active\nsites owing to TNRs’ high surface to volume ratio. (ii) A considerable\nreduction in the charge transfer resistance caused by the direct growth\nof ML-MoS₂ over the TNR array, naturally rendering low\nelectrical loss contacts compared to the conventional transfer process.\nMoreover, the direction of the built-in electric field in the MoS₂/TiO₂ heterostructure also facilitates the flow\nof electrons from the electrode to the electrocatalyst surface, consequently\ndecreasing the charge transfer resistance. (iii) The high intrinsic\nHER activity of the active sites owing to the low Gibbs free energy\nof the catalytic surface (ML-MoS₂@TNRs). Moreover, by virtue\nof the high crystalline quality of ML-MoS₂, the ML-MoS₂@TNRs sample shows excellent stability and working durability.\nClearly, these characteristics suggest that our proposed method has\ngreat potential for practical applications in the form of large-scale\nHER devices.