DEMS study of hydrogen evolution reaction at Ni/reduced graphene oxides/Mo2C composites

Abstract

In the present paper, Ni nanoparticles on graphene-based materials (Ni-GMs) and Mo2C composites (Ni-Mo2C) were tested as electrocatalysts towards the hydrogen evolution reaction (HER) using differential electrochemical mass spectrometry (DEMS) in alkaline medium. Precise determination of the Tafel slope and rate-determining step (RDS), along with the reaction mechanism, was achieved. The findings show that Ni deposition and the addition of Mo2C particles significantly enhance the catalytic activity, leading to low overpotentials towards the HER. Among the tested composites, Ni/rGO/Mo2C demonstrated the best onset potential (-54 mVRHE), followed by Ni/N-rGO/Mo2C (-63 mVRHE) and Ni/SNrGO/Mo2C (-100 mVRHE), with ionic current measurements (m/z = 2) confirming a Volmer-Heyrovsky pathway as the RDS. The addition of Mo2C, while not altering the reaction mechanism, significantly enhanced onset potentials and kinetics, with Tafel slopes for Ni-GMs ranging from 54 to 70 mV·dec−1, underscoring improved HER efficiency. Furthermore, the stability of these composites, particularly Ni/N-rGO/Mo2C, was tested overextended HER operation, showing sustained current densities and reduced degradation. Electrochemical impedance spectroscopy (EIS) revealed that Ni/N-rGO/Mo2C exhibited the lowest charge-transfer resistance, facilitating efficient electron transfer, which likely contributes to its superior durability. The incorporation of heteroatoms such as N and S further enhanced performance by preventing the adverse conductivity effects associated with Mo2C, thereby maintaining high catalytic activity. Collectively, these results indicate that Ni-Mo2C composites could be considered as promising catalysts to be used as cathodes in electrolysers.