The Characterisation of Electrodeposited MoS2 Thin Films on a Foam-Based Electrode for Hydrogen Evolution

Abstract

Molybdenum sulphide is an emerging precious-metal-free catalyst for cathodic water splitting. As its active sites catalyse the Volmer hydrogen adsorption step, it is particularly active in acidic media. This study focused on the electrochemical deposition of MoS2 on copper foam electrodes and the characterisation of their electrocatalytic properties. In addition, the electrodeposition was modified by adding a reducing agent—sodium hypophosphite—to the electrolyte. To reveal the role of hypophosphite, X-ray photoelectron spectroscopy (XPS) analysis was carried out in addition to scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). MoS2 films, electrodeposited at various charges passed through the cell (catalyst loadings), were tested for their catalytic activity towards hydrogen evolution in 0.5 M H2SO4. Polarisation curves and Tafel slope analysis revealed that the electrodeposited MoS2 films are highly active. Namely, Tafel slopes fell within the 40–50 mV dec−1 range. The behaviour of as-deposited films was also evaluated by electrochemical impedance spectroscopy over a wide overpotential range (0 to −0.3 V), and two clear time constants were distinguished. Through equivalent electrical circuit analysis, the experimental data were fitted to the appropriate model, and the obtained values of the circuit components were examined as a function of overpotential. It was found that the addition of NaH2PO2 into the electrodeposition solution affects the intrinsic activity of the material. Finally, a method is proposed to approximate the number of active sites from impedance data.

Femtosecond Laser-Ablated Copper Surface as a Substrate for a MoS2-Based Hydrogen Evolution Reaction Electrocatalyst

“…It is worth noting that the (200) peak became the most intense after depositing a MoS 2 film on the fs-Cu, which probably shows that MoS 2 tends to deposit on the (111) plane. Moreover, an XPS analysis carried out on similarly synthesized films in a previous study confirmed the formation of Mo(IV)-S bonds [ 34 ].…”

“…Electrochemical impedance spectroscopy is a very useful tool in heterogeneous electrocatalyst characterization because it gives the ability to measure certain parameters that are related to the electrochemically active or even electrocatalytically active surface area of the electrode. In previous studies, EIS has been used to compare the electrocatalytic activities of electrodes with an uncertain geometrical surface area [ 34 , 52 ] and a similar approach was applied here. The EIS spectra were obtained at overpotentials where little to moderate hydrogen evolution occurs, depending on the catalytic activity of the electrode (−0.1 V, −0.2 V, −0.3 V).…”

“…The pH of the electrolyte was ~8. Sodium hypophosphite was added because it was found to have a beneficial effect on the Mo-S bond formation during cathodic MoS 2 deposition in a previous study [ 34 ]. The depositions were carried out under potentiostatic conditions at −1.1 V vs. Ag/AgCl by limiting the amount of charge passed through the system to 5 C. The cathodic deposition of MoS 2 occurs as in Equation (1) [ 36 ].…”

“…Additionally, the process is relatively simple, can be carried out at room temperature, and typically yields amorphous and highly electrocatalytically active films. The properties of the electrochemically synthesized films can be tuned by adding certain surfactants/reducing agents such as sodium dodecyl sulfate [ 28 ] or sodium hypophosphite [ 34 ] into the electrodeposition solution. The former was found to have a beneficial effect on the HER electrocatalytic stability of the MoS 2 film, and the latter was observed by X-ray photoelectron spectroscopy (XPS) to promote the formation of Mo(IV)-S bonds and slightly improve the catalytic efficiency of the film.…”

Electrodeposition of Molybdenum Disulfide (MoS2) Nanoparticles on Monocrystalline Silicon

“…The high activity, excellent stability and precious metal-free composition of MoS 2 makes it suitable for performing sustainable and feasible HER electrocatalysis [ 16 ]. Different forms of active HER MoS 2 electrocatalysts have been developed, including crystalline nanoparticles, amorphous films and molecular clusters [ 1 , 3 , 6 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 ]. MoS 2 is also characterized by unique photocatalytic properties [ 3 , 6 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ].…”