The development of noble-metal-free catalysts with high catalytic efficiency and low cost can greatly reduce the cost of hydrogen production in electrolytic water hydrogen production technology. In recent years, molybdenum disulfide (MoS2) has been widely used in hydrogen evolution, and the catalytic activity of MoS2 thin film is closely related to its thickness. This study presents an innovative investigation into the hydrogen evolution reaction (HER) performance of MoS2 coatings with precisely controlled thicknesses which are deposited on nickel foam (NF) substrates. The physical vapor deposition technique, a significant advancement over conventional methods like hydrothermal synthesis or chemical vapor deposition lack of reproducibility and scalability, was utilized. The effect of thickness, a key parameter, on the structural characteristics and electrochemical performance of MoS2 was explored. Four distinct thicknesses of 0.5 μm, 3.8 μm, 5.5 μm, and 11.4 μm were obtained by varying the deposition time while keeping other sputtering parameters constant, allowing for a direct correlation between coating thickness, microstructure, phase composition, and HER activity.
Structural analysis via XRD revealed that all coatings were largely amorphous but exhibited discernible diffraction peaks. Crucially, the (100) peak, indicative of a vertical growth orientation which exposed more active edge sites, became more pronounced with the increasing thickness, particularly in the 5.5 μm sample. Raman spectroscopy and TEM imaging provided a key finding: a phase transition from the semiconducting 2H-MoS2 phase (in the 0.5 and 3.8 μm samples) to a metallic 1T-MoS2 phase (in the 5.5 and 11.4 μm samples) on the coating surface. This transition, likely induced by interlayer sliding from plasma bombardment during sputtering, was critical as the 1T-phase offered superior electrical conductivity. SEM imaging showed that the morphology evolved from small clusters to a typical, porous "worm-like" structure at moderate thicknesses (3.8 and 5.5 μm), which then fractured and became more compact upon excessive thickening (11.4 μm) due to stacking compression and resputtering effects.
Electrochemical performance metrics demonstrated a non-linear relationship between thickness and HER activity, identifying a clear performance optimum. The 5.5 μm coating delivered exceptional HER performance, exhibiting the lowest overpotentials of 138.2 mV and 218.2 mV at current densities of 10 mA/cm2 and 100 mA/cm2, respectively, and the smallest Tafel slope of 76.5 mV/dec, indicating favorable reaction kinetics. This sample also had the lowest charge transfer resistance (Rct = 0.028 Ω), as determined by EIS, facilitating efficient electron transport. Although the thickest sample (11.4 μm) possessed the largest electrochemical active surface area (Cdl = 97.9 mF/cm2) and a metallic surface phase, its HER performance degraded due to a significant increase in Rct (0.1 Ω), caused by excessive electron transport distance and compact stacking.
The thickness-dependent behavior is analyzed from the perspective of three core HER steps (Volmer, electron transfer and desorption). An optimal thickness (~5.5 μm) provides an ideal balance: a porous, vertically-aligned morphology with abundant edge sites for efficient H* adsorption, a metallic 1T-phase surface for optimal adsorption energy, and a moderate thickness ensuring low-resistance electron pathways from the substrate. Conversely, overly thick coatings hinder electrolyte penetration, trap H2 bubbles, and increase internal resistance, disrupting the adsorption-desorption balance and impairing performance. This work provides profound new insights into the role of coating thickness in electrocatalyst design, establishing magnetron-sputtered MoS2 as a highly promising and tunable non-precious metal catalyst for sustainable hydrogen production.
Key words
electrolytic water hydrogen production /
1T-MoS2 /
hydrogen evolution reaction /
coating thickness
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Funding
The SWIP Innovation Action Program (202301XWCX003)；The Project of Leshan Science and Technology Bureau (23GZD014)
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