MoS2/NiS2 Composites for Efficient Hydrogen Evolution Both in Acidic and Alkaline Media

Abstract

The growing concern about global warming, environmental pollution and energy security has raised the demand for clean energy resources in place of fossil fuel. Cost-efficient generation of hydrogen from water-splitting through electrocatalysis holds tremendous promise for clean energy (1, 2). Central to the electrocatalysis are efficient and robust electrocatalysts composed of earth-abundant elements, which are urgently needed for realizing low-cost and high-performance energy conversion devices. Transition metal compounds (TMCs) are a group of attractive noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER). Earth-abundant MoS2 has emerged as a promising hydrogen evolution reaction (HER) catalyst with high activity and durability, but it is kinetically retarded in alkaline media . Extensive efforts have been devoted to improving the HER activity of MoS2 in acid (3), but little attention has been paid to simultaneously enhancing its HER performance both in acid and base. This work demonstrates a dramatic enhancement of HER kinetics both in acidic and alkaline media by hybridizing vertical MoS2 with another earth-abundant material, nickel disulfide (NiS2). Field-emission SEM image shows that the MoS2/NiS2 composite is composed of a film-like structure of NiS2 cover on the edge surfaces of the MoS2 sheets (Figure 1a). As shown in Figure 1b, the XRD peaks observed at 2θ=14.1°, 32.9° and 58.8° of the MoS2/NiS2 sample can be indexed to 2H-MoS2 crystal (JCPDS No. 75-1539), and peaks at 2θ=31.4°, 45.1° and 53.4° indexed to (200), (220) and (311) facets of the NiS2, respectively (JCPDS No. 88-1709). The synthesized MoS2/NiS2 composite exhibits a much lower HER overpotential both in acidic and alkaline media than that of bare MoS2 and NiS2 catalysts (Figure 1c and d). Figure caption Figure 1. (a) FESEM image of the MoS2/NiS2 composite. (b) XRD patterns of the NiS2 and MoS2/NiS2 samples, together with the standard pattern of 2H MoS2 (JCPDS 75-1539) and NiS2 (JCPDS 88-1709). (c) Polarization curves of bare MoS2, NiS2 and MoS2/NiS2 composite catalysts in 0.5 M H2SO4 solution at a scan rate of 5 mV/s. (d) Polarization curves of bare MoS2, NiS2 and MoS2/NiS2 composite catalysts in 1 M KOH solution at a scan rate of 5 mV/s. References D. Strmcnik et al., Improving the hydrogen oxidation reaction rate by promotion of hydroxyl adsorption. Nat. Chem. 5, 300-306 (2013).Y. Jiao, Y. Zheng, M. T. Jaroniec, S. Z. Qiao, Design of electrocatalysts for oxygen- and hydrogen-involving energy conversion reactions. Chem. Soc. Rev. 44, 2060-2086 (2015).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