Synthesis of Carbide Derived Carbon (CDC) By Electrolysis of Molten Chloride Salts

Abstract

Synthesis of Carbide Derived Carbon (CDC) by Electrolysis of Molten Chloride Salts Mariusz Mika, Michael McNallan, Kai-yuan Cheng, Department of Civil and Materials Engineering, University of Illinois at Chicago, 842 w. Taylor St., Chicago, IL 60607 Carbide Derived Carbon (CDC) is a nanostructured porous carbon that is produced by extraction of the metal component from a ceramic carbide by a high temperature reaction. CDC materials are useful in a number of advanced devices, including supercapacators, lithium ion batteries, and tribological systems. [1-3] Carbide derived carbons have been produced by exposing carbide ceramics to vacuum at very high temperatures, by hydrothermal reactions, and by electrochemical processing in room temperature electrolytes,[4,5] but the largest quantities of these materials have been produced by exposing the ceramics to halogen gases, mainly chlorine, at temperatures between 800 and 1200oC, where the high vapor pressures of metal halide species, such as SiCl4, and TiCl4 leads to rapid removal of the metal component. Because this temperature is not sufficiently high to facilitate the crystallization of the carbon into the equilibrium graphite structure, the product is amorphous and nanocrystalline carbon containing nanoscale porosity. The use of chlorine gas to synthesize CDC presents many practical problems due to its corrosive and toxic nature. The system requires close monitoring for safety, and equipment tends to deteriorate rapidly because of exposure to the chlorine. If an application requires synthesis of CDC only on specific locations on the carbide, it is difficult to mask the surface of the carbide from the aggressive gas. As an alternative method to produce CDC, we have prepared CDC on several carbides by electrolysis of molten chloride salts. The apparatus used to produce CDC is shown schematically in Figure 1. The electrolyte was a KCl-NaCl eutectic at temperatures between 750oC and 900oC. Several carbides, including SiC and Ti2AlC have been processed, all resulting in carbide derived carbon synthesis as identified by Raman spectroscopy. The effects of process parameters including precursor carbide, temperature, cell voltage, and temperature will be discussed.