Abstract
Metallic two-dimensional transition-metal dichalcogenides (TMDs) of the group 5 metals are emerging as catalysts for an efficient hydrogen evolution reaction (HER). The HER activity of the group 5 TMDs originates from the unsaturated chalcogen edges and the highly active surface basal planes, whereas the HER activity of the widely studied group 6 TMDs originates solely from the chalcogen- or metal-unsaturated edges. However, the batch production of such nanomaterials and their scalable processing into high-performance electrocatalysts is still challenging. Herein, we report the liquid-phase exfoliation of the 2H-TaS2 crystals by using 2-propanol to produce single/few-layer (1H/2H) flakes, which are afterward deposited as catalytic films. A thermal treatment-aided texturization of the catalytic films is used to increase their porosity, promoting the ion access to the basal planes of the flakes, as well as the number of catalytic edges of the flakes. The hybridization of the H-TaS2 flakes and H-TaSe2 flakes tunes the Gibbs free energy of the adsorbed atomic hydrogen onto the H-TaS2 basal planes to the optimal thermo-neutral value. In 0.5 M H2SO4, the heterogeneous catalysts exhibit a low overpotential (versus RHE, reversible hydrogen electrode) at the cathodic current of 10 mA cm–2 (η10) of 120 mV and high mass activity of 314 A g–1 at an overpotential of 200 mV. In 1 M KOH, they show a η10 of 230 mV and a mass activity of 220 A g–1 at an overpotential of 300 mV. Our results provide new insight into the usage of the metallic group 5 TMDs for the HER through scalable material preparation and electrode processing.
Highlights
Molecular hydrogen (H2) has been touted as an ideal energy carrier with high energy density.[1]
The metallic 2H-transition-metal dichalcogenides (TMDs) based on group 5 metals (i.e., tantalum (Ta), niobium (Nb), and vanadium(V)) have raised paramount appeal for the hydrogen evolution reaction (HER) because of their intrinsic basal plane activity[38−44] that is beyond that of either metal or chalcogen edges.[41−44] The latter statement has been confirmed by density functional theory (DFT) calculations, whose outcomes are summarized in Figure 1.25,39,41,42,45 Clearly, the catalytic properties of their basal planes could make these materials compatible with scalable existing electrode designs
The as-produced flakes have been used in the form of films to catalyze the hydrogen evolution reaction (HER) in both acidic and alkaline media
Summary
Molecular hydrogen (H2) has been touted as an ideal energy carrier with high energy density (between 120 and 140 MJ kg−1).[1]. → 2H2 + The most effective electrocatalysts for the HER are expensive and scarce Pt-group elements.[8−10] the upscaling of electrochemical technology for HER is currently inspiring the search for viable catalyst alternatives,[11−14] including low Pt-content alloys[15−17] or low-cost transition-metal-based alloys, compounds, and heterostructures.[11−13,18] In this context, the transition-metal dichalcogenides (TMDs), made of covalently bonded C−M−C units (M = transition metal; C = chalcogen, i.e., S, Se, Te),[19,20] have attracted strong interest for the HER.[21−24] Theoretical[25−27] and experimental[28−31] investigations have shown that the HER active sites of the natural semiconducting phase (2H) of molybdenum (Mo)- and tungsten (W)-based TMDs are chalcogen-unsaturated edges, since they have a close to zero. Our results furnish a novel guidance to use the metallic group 5 TMDs as efficient HER catalysts by means of scalable material preparation and electrode processing
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