Tunable Pt–MoS_x Hybrid Catalysts for Hydrogen Evolution

Platinum (Pt)-based materials are inevitably among the best-performing electrocatalysts for hydrogen evolution reaction (HER). MoS₂ was suggested to be a potent HER catalyst to replace Pt in this reaction by theoretical modeling; however, in practice, this dream remains elusive. Here we show a facile one-pot bottom-up synthesis of Pt–MoS_x composites using electrochemical reduction in an electrolytic bath of Pt precursor and ammonium tetrathiomolybdate under ambient conditions. By modifying the millimolar concentration of Pt precursors, composites of different surface elemental composition are fabricated; specifically, Pt_1.8MoS₂, Pt_0.1MoS_2.5, Pt_0.2MoS_0.6, and Pt_0.3MoS_0.8. All electrodeposited Pt–MoS_x hybrids showcase low overpotentials and small Tafel slopes that outperform MoS₂ as an electrocatalyst. Tantamount to electrodeposited Pt, the rate-limiting process in the HER mechanism is determined to be the Heyrovsky desorption across Pt–MoS_x hybrids and starkly swings from the rate-determining Volmer adsorption step in MoS₂. The Pt–MoS_x composites are equipped with catalytic performance that closely mirrors that of electrodeposited Pt, in particular the HER kinetics for Pt_1.8MoS₂ and Pt_0.1MoS_2.5. This work advocates electrosynthesis as a cost-effective method for catalyst design and fabrication of competent composite materials for water splitting applications.