Hydrogen evolution activity and electrochemical stability of selected transition metal carbides in concentrated phosphoric acid

• The hydrogen evolution activity (HER) on five transition metal carbides was studied in concentrated phosphoric acid at different temperatures.
• Carbides of Group 6 metals (Cr, Mo, W) showed significant HER activity; the Volmer-Heyrovsky mechanism was proposed for the HER reaction on these materials.
• The electrochemical stability towards oxidation was studied in concentrated phosphoric acid, with Cr, Ta and W carbides showing passivating behavior, while Nb and Mo carbides showed corrosion.

Alternative catalysts based on carbides of Group 5 (niobium and tantalum) and 6 (chromium, molybdenum and tungsten) metals were prepared as films on the metallic substrates. The electrochemical activities of these carbide electrodes towards the hydrogen evolution reaction (HER) in concentrated phosphoric acid were investigated in a temperature range from 80 to 170 °C. A significant dependence of the activities on temperature was observed for all five carbide samples. Through the entire temperature range Group 6 metal carbides showed higher activity than that of the Group 5 metal carbides, attributable to the different electronic structures. Tungsten carbide among the studied electrode samples exhibited the highest HER activity. Upon anodic potential scans in the presence of oxygen, chromium, tantalum and tungsten carbides displayed passivation due to the formation of stable surface layers whereas niobium and molybdenum carbides seemed to undergo corrosion.