Synthesis of binder-free fluffy anemone-like MoS2 for electrocatalytic hydrogen evolution: A Mott-schottky study

Abstract

Highly active anemone-like MoS2 catalyst was vertically and directly deposited on fluorine-doped tin oxide (FTO) substrate via a straightforward facile hydrothermal method with excellent adhesion and appreciable stability for hydrogen evolution reaction (HER). MoS2 catalyst with unique morphology full of active edge sites and surface areas was fabricated by varying synthesis time and specific concentration of precursors. Structural characteristics were investigated by X-ray diffraction pattern (XRD), and Raman spectroscopy. Field emission scanning electron microscopy (FESEM) images show the variation of morphology during synthesis time as a very important factor in the preparation process. It also reveals the lamellar structure of anemone-like MoS2 with an average thickness of ~19 nm. Electrochemical tests including linear sweep voltammetry and electrochemical impedance spectroscopy were carried out. These tests suggest a high electrocatalytic activity for MoS2/FTO electrode toward HER with a charge transfer resistance (Rct) about 24 Ω, a Tafel slope of ~87 mV dec−1, and an exchange current density of 0.063 mA cm−2 for the optimum sample synthesized at 20 h during hydrothermal process. The catalytic activity of the samples for HER was carefully investigated and proposed in detailed discussions according to the Mott-Schottky equation for the first time. Based on Mott-Schottky analysis, the obtained samples are n-type semiconductors and the density of carriers (ND) of samples was calculated. ND of the optimum sample (sample B) obtained (2.23 ± 0.055) × 1017. Fabricated samples have good stability proved by repeating LSV test for 1000 cycles. This work optimizes the catalytic activity of the bare MoS2 with a cost-effective, easy, and binder-free method. It is a promising base for future works on MoS2 catalysts.