Abstract
Molybdenum disulfide (MoS2) is a highly promising catalyst for the hydrogen evolution reaction (HER) to realize large-scale artificial photosynthesis. The metallic 1T′-MoS2 phase, which is stabilized via the adsorption or intercalation of small molecules or cations such as Li, shows exceptionally high HER activity, comparable to that of noble metals, but the effect of cation adsorption on HER performance has not yet been resolved. Here we investigate in detail the effect of Li adsorption and intercalation on the proton reduction properties of MoS2. By combining spectroscopy methods (infrared of adsorbed NO, 7Li solid-state nuclear magnetic resonance, and X-ray photoemission and absorption) with catalytic activity measurements and theoretical modeling, we infer that the enhanced HER performance of LixMoS2 is predominantly due to the catalytic promotion of edge sites by Li.
Highlights
Like other transition-metal dichalcogenides (TMDs), MoS2 can exist in different polymorphs, that is, the 2H, 1T′, and 3R phases.[1]
By tuning the arrangement of the S atoms, MoS2 can convert from the semiconducting 2H to the metallic 1T′ phase
For instance, trace metal impurities are known to play an active role in determining the electrocatalytic properties of graphene,[19] the role of adsorbed Li in the MoS2-catalyzed hydrogen evolution reaction (HER) remains ambiguous
Summary
Letter devoted to synthesis strategies that can expose more active (edge) sites to enhance the overall HER performance, for ebxaasmal ppllea,nneasnwopitahrtsiuculfluartevaMcaonSc2i,ensa.2n4o−s2t6ruInctucorendtrMastoSw2i,tohritMs o2SH2 counterpart, the significant catalytic improvement toward HER of 1T′-MoS2 has been ascribed to the intrinsic activity of its basal planes.[8]. Li1.00MoS2 and Li2.06MoS2, the relatively lower catalytic activity of these samples compared with that of Li0.29MoS2 (entirely 2H phase) indicates that next to Li intercalation, Li adsorption plays a key role in describing the high HER activity of LixMoS2 electrocatalysts.[28,41−43]. The more optimum ΔGH* values predicted at lower Li concentrations at the Mo edge compared with the S edge demonstrate a superior HER activity of the Mo edges This is consistent with previous theoretical predictions that showed the Mo edges to be more active for HER than S edges.[46,47] Further insights into the adsorption of H on the Mo edge of the LixMoS2 materials were gained through a Bader charge and electron density difference isosurface analyses.
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