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, Pt1.8MoS2, Pt0.1MoS2.5, Pt0.2MoS0.6, and Pt0.3MoS0.8. 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 Pt1.8MoS2 and Pt0.1MoS2.5. This work advocates electrosynthesis as a cost-effective method for catalyst design and fabrication of competent composite materials for water splitting applications.

Morphological Effects and Stabilization of the Metallic 1T Phase in Layered V-, Nb-, and Ta-Doped WSe2 for Electrocatalysis.

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-MoS2 as an electrocatalyst witnessed in previous reports spurred us to examine the effect of doping WSe2 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 WSe2 materials are found to possess largely identical inherent electrochemistry to the undoped WSe2 with a characteristic anodic peak. Living up to expectations, the Group 5 transition-metal-doped WSe2 materials exhibit improved electrocatalytic HER efficiency, as evident by the lower HER overpotentials and Tafel slopes relative to undoped WSe2 . 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 WSe2 to thinner fragments in doped WSe2 . Although undoped WSe2 exists in the semiconducting 2H phase, the Group 5 transition-metal-doped WSe2 materials are dominated by the metallic 1T phase. Doping WSe2 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 WSe2 upon doping, Group 5 transition-metal dopants proved futile in activating the ORR electrocatalytic behavior of WSe2 , 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 WSe2 relative to their morphological features and provide an evaluation of the efficacy of doping TMDs in electrocatalytic applications.