Insights into electrodeposition and catalytic activity of MoS2 for hydrogen evolution reaction electrocatalysis

Abstract

MoS2-x films were electrodeposited cathodically onto copper rod substrates from a solution, containing MoS4 2as the common Mo and S ion precursor. The catalyst loading was varied by adjusting electrodeposition conditionsapplied potential and deposition time. A typical set of HER electrocatalyst experiments (polarization, Tafel slope analysis) carried out in 0.5 M H2SO4 was applied on the deposited MoS2-x films. Analysis of surface morphology (SEM) and chemical composition (EDS) were also performed. Electrochemical impedance spectroscopy in the same acidic media was used to evaluate the catalyst-solution interface and the interfacial kinetics (by calculating double layer capacitance and charge transfer resistance), as well as characterize the hydrogen adsorption process (adsorption capacitance and resistance). A linear correlation between electrodeposition time and double layer capacitance was observed. However, the charge transfer resistance was found to decrease until it plateaued at longer deposition times. The MoS2-x film, deposited for 7200 s at -1.0 V (vs. Ag/AgCl), reached 10 mA cm -2 HER current at -0.18 V (vs. RHE), and represented the best result of this study. Electrochemical impedance spectroscopy (EIS) was further applied to evaluate the subtle changes in the MoS2-x films' semiconductor properties after HER stability tests (at -40 mA cm -2 ), and to estimate the number of active sites on the material. EIS, in comparison to cyclic voltammetry or roughness factor calculations, is a completely non-destructive method that can be applied to accurately assess the system under investigation.

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

“…Therefore, a cathodic current of 10 mA corresponding to a potential, where intense hydrogen evolution does not yet occur, was selected. At this current, the potential settles at ~1.05 V, which is almost identical to the one we used for potentiostatic deposition in the precluding research [34]. The films were electrodeposited at increasing charges passed through the cell (from 10 to 40 C).…”

“…Molybdenum disulphide films were electrodeposited from a tetrathiomolybdate (MoS 4 2− /TTM) solution, containing 25 mM MoS 4 2− and 0.1 M Na 2 SO 4 . This base solution was prepared via a chemical four-step sulphidation of molybdate reaction, as described in our previous work [34], but without additional surfactants. The pH of the solution was kept neutral at~pH 7, to prevent precipitation of insoluble MoS 3 and suppress hydrogen evolution during electrodeposition.…”

“…Earlier, our group reported on the HER electrocatalytic activity of electrodeposited MoS 2−x films and the application of electrochemical impedance spectroscopy (EIS) to characterise them [34]. EIS can provide kinetic information additional to steady-state measurements and allows the determination of reaction rate constants [6], charge transfer kinetics [35] and double layer capacitance, which is proportional to the electrocatalytically active surface area [36,37].…”

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

“…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).…”

Strategies to improve electrocatalytic and photocatalytic performance of two-dimensional materials for hydrogen evolution reaction

“…However, bulk MoS2 shows poor HER performance owing to the exposure of few active sites and the uncoordinated effect of the active sites located at the Mo-S edges due to the superposition of van der Waals force in its interior. Atoms in the layers are covalently bound, resulting in undesirable HER performance [49,50]. In addition, bulk MoS2 has the disadvantage of low electronic conductivity.…”