Platinum (Pt)-based materials are inevitably among the best-performing electrocatalysts for hydrogen evolution reaction (HER). MoS 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 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, PtMoS, PtMoS, PtMoS, and PtMoS. All electrodeposited Pt-MoS hybrids showcase low overpotentials and small Tafel slopes that outperform MoS 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 hybrids and starkly swings from the rate-determining Volmer adsorption step in MoS. The Pt-MoS composites are equipped with catalytic performance that closely mirrors that of electrodeposited Pt, in particular the HER kinetics for PtMoS and PtMoS. This work advocates electrosynthesis as a cost-effective method for catalyst design and fabrication of competent composite materials for water splitting applications.

Layered transition-metal dichalcogenides (TMDs) are valued for their electrocatalytic properties toward the hydrogen-evolution reaction (HER) and oxygen-reduction reaction (ORR). One effective strategy to activate the electrocatalytic properties of TMDs is through doping. The optimistic outlook of doped-MoS as an electrocatalyst witnessed in previous reports spurred us to examine the effect of doping WSe with Group 5 transition-metal species, namely V, Nb, and Ta, in aspects of inherent electroactivities and catalysis. Apart from the mild reduction signal unique to the Group 5 transition-metal dopants, the Group 5 transition-metal-doped WSe materials are found to possess largely identical inherent electrochemistry to the undoped WSe with a characteristic anodic peak. Living up to expectations, the Group 5 transition-metal-doped WSe materials exhibit improved electrocatalytic HER efficiency, as evident by the lower HER overpotentials and Tafel slopes relative to undoped WSe . After doping with V, Nb, or Ta species, an increased number of active sites is observed given the distinct changes in morphology from thick bulky pieces in undoped WSe to thinner fragments in doped WSe . Although undoped WSe exists in the semiconducting 2H phase, the Group 5 transition-metal-doped WSe materials are dominated by the metallic 1T phase. Doping WSe with V, Nb, or Ta stabilizes the catalytic 1T phase and appears to induce the transition from the 2H to 1T phase. In contrast to the enhanced HER performance of WSe upon doping, Group 5 transition-metal dopants proved futile in activating the ORR electrocatalytic behavior of WSe , for which the ORR efficiency is unchanged. Therefore, these findings facilitate the understanding of the role of Group 5 transition-metal dopants in the electrochemical and catalytic properties of WSe relative to their morphological features and provide an evaluation of the efficacy of doping TMDs in electrocatalytic applications.

No abstract

No abstract