Mechanism of hydrogen generation on stable Mo-edge of 2H-MoS 2 in water from density functional theory
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Mechanism of hydrogen generation on stable Mo‑edge of 2H‑MoS2 in water from density functional theory Yan‑Xia Han1 · Chao Kong1 · Pen‑Ji Yan2 Received: 27 February 2020 / Accepted: 25 May 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract In this paper, the stable structure of Mo-edge of 2H-MoS2 in water and the H 2 evolution mechanism at Mo-edge in 2H-Mo7S17 cluster were investigated by the B3LYP method of the density functional theory. The calculations suggested that the stable structure of the Mo-edge in gas and water was different. The Mo-edge with the upright S bonded by one Mo atom was more stable in water while the S atom of Mo-edge was bonded by two Mo atoms to generate a stable Mo-edge in gas. The adsorption energy of H on S was higher than that on Mo at Mo-edge; as a result, the hydrogen evolution reactions on S and Mo were limited by the Heyrovsky and Volmer step, respectively. In hydrogen evolution reaction, the Volmer reaction occurs on S to produce Mo7S17HS, leading to the aggregation of electron on Mo and thus decreasing the barriers for H2 evolution reaction on Mo. Subsequently, the Mo in Mo7S17HS severing as active sites efficiently catalyzed hydrogen evolution reaction through the Volmer–Heyrovsky mechanism, in which the Volmer reaction was identified as the rate-determining step with a potential barrier of 17.9 kcal/mol, being close to the experimental value of 19.9 kcal/mol. Keywords 2H-MoS2 · Mo-edge · H2 generation · Volmer–Heyrovsky · DFT
1 Introduction The conversion of solar energy into hydrogen energy through photocatalytic water splitting is one of the most ideal methods to solve energy problem [1–7]. However, the activity of catalyst is a critical factor in restricting the wide applications of H2 generation by photocatalytic water splitting. Noble metals, such as Pt and its alloys as co-catalyst, have shown the best catalytic activity for photocatalytic H2 evolution due to their low overpotential for proton reduction [4–6]. However, the scarceness of Pt limits the large-scale applications. Recently, molybdenum disulfide (MoS2), as an alternative and cheap hydrogen evolution reactions (HER) catalyst, has Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00214-020-02614-y) contains supplementary material, which is available to authorized users. * Chao Kong [email protected] 1
College of Chemistry and Chemical Engineering, Longdong University, Qingyang 745000, China
College of Chemistry and Chemical Engineering, Hexi University, Zhangye 734000, China
2
attracted increasing attentions in electrocatalytic and photocatalytic HER [8–14]. Typically, the crystalline M oS2 exists in more stable 2H phase [15]. The basal plane of 2H-MoS2 monolayer is catalytically inert for HER since the Mo and S atoms reach their respective saturation states, and the Mo-edge is identified as an active site experimentally and theoretically [16]. Nørskov et al. have proposed that the unsaturated S atoms a
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