Comparison of electrochemical stability of transition metal carbides (WC, W2C, MO2C) over a wide pH range

Transition metal carbides have shown potential for use in electrochemical applications as low-cost catalysts or catalyst support materials. In order to determine which transition metal carbides are suitable for specific electrochemical applications, it is necessary to determine their stability in electrolytic solutions of varying pH values. In this work we compare the stability of the most commonly used carbides: tungsten carbides (WC and W2C) and molybdenum carbide (MO2C). Cyclic voltammetry (CV) is used to determine the onset of oxidation and the hydrogen evolution reaction (HER) at discrete pH values while chronopotentiometric (CP) titrations are used to create potential-pH 'stability maps', which designate the regions of stability, passivation, and oxidation. Based on the slopes of the boundaries between the regions of stability, information about the oxidation mechanisms is obtained through the Nernst equation, indicating key differences in the electrochemical behavior of each surface. WC exhibits enhanced resistance to surface oxidation in acidic solution and comparable stability in neutral/alkaline solution to MO2C and W2C. (C) 2011 Elsevier B.V. All rights reserved.