Analysis of the electrocatalytic activity of a-molybdenum carbide thin porous electrodes toward the hydrogen evolution reaction

In the last years, transition metal carbides have appeared as novel materials with promising catalytic properties toward important practical reactions. In this work, the use of the thin porous electrodes for evaluating the hydrogen evolution reaction (HER) of hexagonal molybdenum carbides (alpha-Mo2C)-based materials is analyzed and the effect of catalyst's load, L-cat, and catalyst's dispersion are discussed in terms of kinetic parameters calculated by employing the electrode geometric area. Catalysts were characterized by X-ray diffraction, energy dispersive X-ray analysis, X-ray photoelectron spectroscopy, cyclic voltammetry and differential electrochemical mass spectrometry. Results have shown that, even for the same catalyst, mass activities and specific activities depend on Lcat. and catalyst's dispersion. In contrast, intrinsic kinetic parameters, calculated from double layer capacitance normalizations, can be considered rather constant. XPS analysis of samples under different electrochemical treatments reveals a surface enrichment of carbon terminated planes after the HER, suggesting a higher HER activity on these planes. An investigation of the electrochemical oxidation of alpha-Mo(2)Cand the catalyst's HER activity show a direct correlation between active sites for HER and active sites for catalyst oxidation. Therefore, this oxidation is also used to estimate HER intrinsic parameters. Finally, the activity of a composite sample, in which alpha-Mo2C is the only active component, is also evaluated. (C) 2016 Elsevier Ltd. All rights reserved. (AU)