High Electrocatalytic Response of Ultra-refractory Ternary Alloys of Ta-Hf-C Carbide toward Hydrogen Evolution Reaction in Acidic Media

Transition metal carbide alloys are promising materials to replace platinum as electrodes in electrocatalysts toward the hydrogen evolution reaction (HER). Although tantalum hafnium carbides (Ta-Hf-C) have shown outstanding refractory and structural properties, there is no clear role of their electrochemical efficiency. Here we report on the electrochemical activity of such thin films, (Ta₂C)_(100-x)%·(Hf₂C)_(x)%, x = 100, 70, 30, and 0, deposited by magnetron sputtering. Grazing incidence X-ray diffraction showed no evidence of phase segregation, and XPS confirms the well-controlled stoichiometry of the electrodes. The HER kinetics was studied in strong acidic conditions, and it was found that the (Ta₂C)_70%·(Hf₂C)_30% was the most active material toward HER in this acid media and displayed an onset overpotential of -198 mV vs NHE and a Tafel slope of 129 mV·dec^-1. Our results suggest that the strong affinity of Hf-C toward oxygen reduction reaction could be responsible for the high catalytic response and strong oxidation resistance of the ternary carbide alloys. Finally, we show that, in fact, the Ta-Hf-C alloys can be competitive materials toward HER.