Effect of H2 Plasma Modification on the Electrocatalytic Hydrogen Evolution Performance of MoS2

Abstract

The hydrogen evolution reaction (HER) is the cathodic half reaction of electrocatalytic water splitting and is thus highly desirable to power the "hydrogen-based economy". Earth-abundant MoS2 has emerged as a promising HER catalyst with high electrocatalytic activity and stability due to its unique physical and chemical properties (1, 2). In the electronic structure of MoS2, the orbitals of HOMO states are mainly localized at the edged S sites, so that the localized electrons are mainly at the edge of MoS2 for charge exchange of proton (3). Extensive efforts have been devoted to developing MoS2 nanostructures to maximize the number of active edge sites, but little attention has been paid to activating the MoS2 basal planar structure. In this work, we used the H2 plasma modification to engineer the planar S-vacancies of MoS2 for enhancing the HER kinetics. Moreover, controlled plasma exposure time has been designed to explore the influence of H2 plasma on the HER performance of MoS2 catalysts. Our experimental results show that the S/Mo atomic ratios decrease with increase the H2 plasma exposure time (Figure 1a). More importantly, the HER performance is becoming better after H2 plasma modification (Figure 1b). the MoS2 H2-plasma 1200s catalyst exhibits a boosted HER activity with the overpotential as low as 92 mV at the current density of 10 mA/cm2 and striking turnover frequency per surface Mo atom (TOF) as 0.0044 s-1, better than most reported MoS2-based catalysts (Figure 1c and d). Figure Caption Figure 1. (a) Atomic ratio of S/Mo for MoS2 samples as the function of H2 plasma exposure time. (b) Polarization curves of H2 plasma treated MoS2 catalysts in 0.5 M H2SO4 solution at a scan rate of 5 mV/s. (c) Overpotential at 10 mA/cm2 and (d) TOF of the H2 plasma treated MoS2 catalysts. References X. Huang, Z. Zeng, H. Zhang, Metal dichalcogenide nanosheets: preparation, properties and applications. Chem. Soc. Rev. 42, 1934-1946 (2013).H. T. Wang et al., Electrochemical tuning of vertically aligned MoS2 nanofilms and its application in improving hydrogen evolution reaction. P. Natl. Acad. Sci. USA 110, 19701-19706 (2013).J. Hu et al., Engineering stepped edge surface structures of MoS2 sheet stacks to accelerate the hydrogen evolution reaction. Energy Environ. Sci. 10, 593-603 (2017). Figure 1