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Transition metal atom doping of the basal plane of MoS₂ monolayer nanosheets for electrochemical hydrogen evolution.

ABSTRACT: Surface sites of extensively exposed basal planes of MoS₂ monolayer nanosheets, prepared via BuLi exfoliation of MoS₂, have been doped with transition metal atoms for the first time to produce 2D monolayer catalysts used for the electrochemical hydrogen evolution reaction (HER). Their HER activity is significantly higher than the corresponding thin and bulk MoS₂ layers. HAADF-STEM images show direct proof that single transition metal atoms reside at the surface basal sites, which subtly modify the electro-catalytic activity of the monolayer MoS₂, dependent on their electronic and stereospecific properties. It is found that these dopants play an important role in tuning the hydrogen adsorption enthalpies of the exposed surface S atoms and Mo atoms in HER. We report electrochemical testing, characterization and computational modelling and demonstrate that Co can significantly enhance the HER activity by the dominant Co-S interaction, whereas Ni substantially lowers the HER rate due to the Ni-Mo interaction at the same basal site. The two transition metal dopants show opposite doping behavior despite the fact that they are neighbors in the periodic table.

SUBMITTER: Lau THM

PROVIDER: S-EPMC5975547 | biostudies-literature | 2018 Jun

REPOSITORIES: biostudies-literature

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Transition metal atom doping of the basal plane of MoS2 monolayer nanosheets for electrochemical hydrogen evolution.

Lau Thomas H M THM Lu XiaoWei X Kulhavý Jiří J Wu Simson S Lu Lilin L Wu Tai-Sing TS Kato Ryuichi R Foord John S JS Soo Yun-Liang YL Suenaga Kazu K Tsang Shik Chi Edman SCE

Chemical science 20180430 21

Surface sites of extensively exposed basal planes of MoS2 monolayer nanosheets, prepared via BuLi exfoliation of MoS2, have been doped with transition metal atoms for the first time to produce 2D monolayer catalysts used for the electrochemical hydrogen evolution reaction (HER). Their HER activity is significantly higher than the corresponding thin and bulk MoS2 layers. HAADF-STEM images show direct proof that single transition metal atoms reside at the su ...[more]

PMID: 29910927

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Project description:Two dimensional (2D) semiconductor materials, such as molybdenum disulfide (MoS2) have attracted considerable interest in a range of chemical and electrochemical applications, for example, as an abundant and low-cost alternative electrocatalyst to platinum for the hydrogen evolution reaction (HER). While it has been proposed that the edge plane of MoS2 possesses high catalytic activity for the HER relative to the "catalytically inert" basal plane, this conclusion has been drawn mainly from macroscale electrochemical (voltammetric) measurements, which reflect the "average" electrocatalytic behavior of complex electrode ensembles. In this work, we report the first spatially-resolved measurements of HER activity on natural crystals of molybdenite, achieved using voltammetric scanning electrochemical cell microscopy (SECCM), whereby pixel-resolved linear-sweep voltammogram (LSV) measurements have allowed the HER to be visualized at multiple different potentials to construct electrochemical flux movies with nanoscale resolution. Key features of the SECCM technique are that characteristic surface sites can be targeted and analyzed in detail and, further, that the electrocatalyst area is known with good precision (in contrast to many macroscale measurements on supported catalysts). Through correlation of the local voltammetric response with information from scanning electron microscopy (SEM) and atomic force microscopy (AFM) in a multi-microscopy approach, it is demonstrated unequivocally that while the basal plane of bulk MoS2 (2H crystal phase) possesses significant activity, the HER is greatly facilitated at the edge plane (e.g., surface defects such as steps, edges or crevices). Semi-quantitative treatment of the voltammetric data reveals that the HER at the basal plane of MoS2 has a Tafel slope and exchange current density (J0) of ∼120 mV per decade and 2.5 × 10-6 A cm-2 (comparable to polycrystalline Co, Ni, Cu and Au), respectively, while the edge plane has a comparable Tafel slope and a J0 that is estimated to be more than an order-of-magnitude larger (∼1 × 10-4 A cm-2). Finally, by tracking the temporal evolution of water contact angle (WCA) after cleavage, it is shown that cathodic polarization has a 'self-cleaning' effect on the surface of MoS2, consistent with the time-independent (i.e., time after cleavage) HER voltammetric response.

Dataset Information

Transition metal atom doping of the basal plane of MoS₂ monolayer nanosheets for electrochemical hydrogen evolution.

Publications

Transition metal atom doping of the basal plane of MoS<sub>2</sub> monolayer nanosheets for electrochemical hydrogen evolution.

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