Carbide-derived Carbon (CDC) has been demonstrated to be an excellent electrode material for electrochemical devices including supercapacitors due to its chemical and electrochemical stability, large specific surface area and controllable pore size and morphology. Currently, CDC is prepared from metal carbides by chlorination in a chlorine gas atmosphere at temperatures of 350 • C or higher. In this paper, conversion using electrochemical methods is reported, which can be achieved by oxidizing vanadium carbides (VC or V 2 C) in aqueous solutions at room temperature and a mild electrode potential to prepare CDC thin film as electrode materials for "on-chip" supercapacitiors. It was found that VC and V 2 C can both be oxidized at a potential of about 0.4 V vs. Ag/AgCl or higher in neutral, acidic, or basic solutions. After the oxidation, vanadium is readily detected in the electrolyte solutions by ICP-MS (Inductively Coupled Plasma -Mass Spectrometry). The so-produced CDC thin film electrode (ca. 2.0 -2.6 μm thick) has a porous morphology and bears specific double layer capacitance values as high as 0.026 F.cm −2 (or 130 F.cm −3 ) with some dependence on the oxidation potential, time, and electrolyte solutions. Carbide-Derived carbon (CDC) is a new type of porous carbon material demonstrating high purity, a narrow distribution of pore sizes, and significant specific surface area.1,2 Due to these unique properties, CDC was found to be very useful for gas storage, flow sensors, and as an electrode material for electrochemical energy storage devices such as supercapacitors.3-7 Currently, the most reliable method to synthesize CDC is to remove the metal or metalloid elements selectively from binary or ternary carbide precursors. 1,8,9 This has been achieved by chlorine gas treatment (chlorination) at a temperature of 350• C or higher. At an elevated temperature, metal / metalloid elements can be reacted to be volatile metal chlorides and purged using an argon gas stream. Thus, the left-over carbon is metal free and sp 2 or sp 3 hybridized. To date, CDC has been successfully synthesized from binary carbides such as TiC, Cr 3 C 2 , Fe 3 C, Mo 2 C, Nb 2 C, SrC 2 , Ta 2 C, VC, V 2 C WC, W 2 C, ZrC, as well as ternary carbides (also called MAX phase carbides) such as Ti 2 AlC, Ti 3 AlC 2 . Most of this work has been performed in bulk solids/powders. Depending on the crystalline/ elemental structure of the precursor and the reaction temperature, the pore size of CDC can be controlled in the range over 2-50 nm.1 The theoretical bulk porosity is between 50-90% in volume. Thus far, the Cl 2 reaction method of etching has been primarily used but one downside is that the Cl 2 gas is toxic, corrosive and the process itself is relatively expensive. On the other hand, an alternative oxidation method is to prepare CDC under more environmentally favorable conditions that have been rarely explored. For example, Y. Gogotsi and coauthors reported the electrochemical etching of MAX-phase carbides to produce CDC at room temperature using ...

Transition metal carbides have unique properties such as high hardness, high melting temperatures, high thermal conductivity, and high chemical stability. In this report, we investigate the electrochemical oxidation of a series of metal carbides including NbC, Nb 2 C, TaC, Ta 2 C, VC, VCrC, TiC and TiCrC in neutral, basic, or acidic aqueous solutions. Cyclic voltammetry and elemental analysis demonstrated that many of these metal carbides can be electrochemically oxidized at low electrode potentials to produce soluble metal ions in the solutions. Carbon in the metal carbides remains on the electrode substrates and forms porous carbide-derived carbon (CDC). The surface morphology of the CDC and specific surface area depend on the metal carbide precursors and the electrochemical oxidation conditions. © Transition metal carbides have extensive applications in many areas of the chemical and mechanical industries.1,2 For example, the refractory and hard ceramic material niobium carbides (NbC and Nb 2 C) have been broadly used as coatings for cutting tool bits and to improve wear resistance. Several transition metal carbides resemble the valence electron structures and the catalytic properties of metals such as Pt and Pd.2-5 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. 6,7 Pt nanoparticles demonstrate superior catalytic effects when they are loaded on WC or W 2 C powders for many reactions such as hydrogen oxidation, hydrogen evolution, alcohol oxidation, and oxygen reduction reactions. 8Due to their chemical stability and poor sintering ability, research on the chemical properties of the metal carbides is restricted to limited areas. 1,9 Metal carbides can be oxidized at higher temperatures with different oxidants. For example, NbC powder can be oxidized in an oxygen atmosphere at 420-600• C to produce Nb 2 O 5 . 10 At a temperature of 350• C or higher, most carbides can react with chlorine gas to form volatile metal chloride (MCl 4 ). The left-over porous CDC is metal free and sp 2 or sp 3 hybridized. 11,12 At room temperature, metal carbides are very stable in strong acidic solutions. However, when an electrical potential is applied, metal carbides can also be oxidized to form metal oxides. 3,13 In addition to the binary metal carbides, MAX phase metal carbides (Ti 3 AlC 2 , Ti 2 AlC and Ti 3 SiC 2 ) can be oxidized in acidic electrolyte solutions (HCl and HF) by electrochemical etching and yield CDC with uniformly distributed nanoscale pores.14,15 In a previous report, binary metal carbides (VC and V 2 C) were electrochemically etched in acidic, neutral, or basic aqueous solutions and produced CDC materials that were excellent electrode materials for electronic double layer supercapacitors. 16In this paper, we investigate the electrochemical properties of a series of metal carbides, NbC, Nb 2 C, TaC, Ta 2 C, VC, VCrC, TiC and TiCrC in aqueous solutions with the presence of HCl, HF, K...

Transition metal carbides have unique properties such as high hardness, high melting point, high thermal conductivity, and high chemical stability. At a temperature of 350 o C or higher, some metal carbides can react with chlorine gas to form volatile metal chlorides. At room temperature, metal carbides are very stable in several strong acid solutions. However, metal carbides can be oxidized electrochemically. Then, metal oxides can be produced and dissolved in the solutions. In this report, we investigate the electrochemical properties of a series of metal carbides including NbC, Nb2C, TaC, and Ta2C in aqueous solutions with the presence 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.