Hydrogen evolution reaction from bare and surface-functionalized few-layered MoS nanosheets in acidic and alkaline electrolytes.

Hydrogen is considered as an ideal and sustainable energy carrier because of its high energy density and carbon-free combustion. Electrochemical water splitting is the only solution for uninterrupted, scalable, and sustainable production of hydrogen without carbon emission. However, a large-scale hydrogen production through electrochemical water splitting depends on the availability of earth-abundant electrocatalysts and a suitable electrolyte medium. In this article, we demonstrate that hydrogen evolution reaction (HER) performance of electrocatalytic materials can be controlled by their surface functionalization and selection of a suitable electrolyte solution. Here, we report syntheses of few-layered MoS nanosheets, NiO nanoparticles (NPs), and multiwalled carbon nanotubes (MWCNTs) using scalable production methods from earth-abundant materials. Magnetic measurements of as-produced electrocatalyst materials demonstrate that MoS nanoflakes are diamagnetic, whereas surface-functionalized MoS and its composite with carbon nanotubes have strong ferromagnetism. The HER performance of the few-layered pristine MoS nanoflakes, MoS/NiO NPs, and MoS/NiO NPs/MWCNT nanocomposite electrocatalysts are studied in acidic and alkaline media. For bare MoS, the values of overpotential (η) in alkaline and acidic media are 0.45 and 0.54 V, respectively. Similarly, the values of current density at 0.5 V overpotential are 27 and 6.2 mA/cm in alkaline and acidic media, respectively. The surface functionalization acts adversely in the both alkaline and acidic media. MoS nanosheets functionalized with NiO NPs also demonstrated excellent performance for oxygen evolution reaction with anodic current of ~60 mA/cm and Tafel slope of 78 mVdec in alkaline medium.