This study offers a kinetic exploration of the Hydrogen Evolution Reaction (HER) in an acidic environment using a catalyst of MoSx modified with electrodeposited platinum atoms (Pt-MoSx). Scanning electron microscopy and high-resolution transmission electron microscopy images revealed a two-dimensional network structure of Pt-MoSx. The linear sweep voltammetries in a 0.5 mol/L H2SO4 solution demonstrated a high catalytic activity of the modified catalyst: an onset potential for hydrogen reduction reaction much more positive than that observed for MoSx, high mass activity (16.5 A/mg at an overpotential of −50 mV), a turnover frequency of 50 H2/s per surface site at a kinetic current density of 10 mA/cm2, and an overpotential of −39 mV. Based on classical models, including the Butler-Volmer equation, Kouteck-Levich equation, and Langmuir isotherm, essential kinetic parameters were obtained. The models in the frequency domain allowed the determination of the surface concentration of molecular hydrogen and the proposition of a transfer function for both dc frequency and infinite rotating disk speed conditions, enabling the determination of the exchange current density (8.51 × 10-4 A/cm2) and Tafel slope (40 mV/dec); the latter value suggested that the reaction proceeds through a Volmer-Heyrovsky pathway, predominantly limited by the Heyrovsky step. Based on the observed electrocatalytic behavior and the measured and calculated parameters, our findings suggest that the electrodeposition of small amounts of Pt on MoSx may represent a promising strategy for molecular hydrogen production.

We are grateful to FAPESP (Projects 2021/12735-1 and 2017/11986-5) and CNPq (Project 140499/2021-0) for financial support.

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