Electrochemical Oxidation of Niobium and Tantalum Carbides in Aqueous Solutions

Transition metal carbides have unique properties such as high hardness, high melting point, high thermal conductivity, and high chemical stability. Transition metal carbides have extensive applications in many areas. For example, the refractory and hard ceramic material Niobium carbides (NbC and Nb2C) can be used in tool bits for cutting tools and materials for wearing resistance. It has been reported that early transition metal carbides resembled the valance electron structures and the catalytic properties metals such as Pt and Pd. The metal carbides or the carbide-derived carbon CDC obtained from these metal carbide precursors can be used as supports to reduce the overall loading of the precious metals. Due to its chemical stability and poor sintering ability, research about chemical properties of carbides is restricted in limited areas. Metal carbides can be oxidized at higher temperature with different oxidants such as chlorine or oxygen. At a temperature of 350 oC or higher, metal carbides can react with chlorine gas to be volatile metal chlorides. At room temperature, metal carbides are very stable in many strong acid solutions. However, when electrical potential is applied, metal carbides can be oxidized and metal oxides can be produced and dissolved in solutions. In this report, we investigate the electrochemical properties of a series of metal carbides, NbC, Nb2C, TaC, Ta2C, VC, and V2C in aqueous solutions with the presents of HCl and HF. Cyclic voltammetry and elemental analysis demonstrated that all of these metal carbides can be oxidized electrochemically at a “mild” electrode potential and produce soluble metal ions in the solutions. The CDC on the surface of the electrode after oxidation is porous and either sp3 or sp2 hybridized.