Novel Approach to the Formation of Carbide-Derived Carbons Using NH4Cl

Abstract

Carbide-derived carbons (CDCs) are traditionally prepared via high-temperature (>200°C) chlorination (Cl2) of metal carbides for research and commercial applications including supercapacitors. This study investigates an alternative CDC synthesis method using an inexpensive halogen-containing etchant, ammonium chloride (NH4Cl), to produce porous CDCs with tunable microstructures. Metal carbide (MexC) powder was mixed with NH4Cl salt and brought to set temperatures ranging from 300-800°C for 2-15 hrs. Reactor designs consisted of an open, tube or box furnace, system with flowing argon or air environments, or the mixture was sealed in an evacuated quartz ampule with Pair,initial= ~1e-2 mbar and Pmax= 20 bar. Scanning electron microscopy (SEM) images show a developing porous layer on the surface of the MexC particles following the core-shell growth model. Auger electron spectroscopy (AES) of the carbon KLL region was used to determine the resulting allotrope of the MexC-CDC powders. When titanium carbide (TiC) was used as the CDC precursor, AES spectra were indicative of a surface transition from metal carbide to graphitic carbon. Furthermore, preliminary N2 adsorption measurements signified that the MexC mass loss and pore growth was associated with an increase in surface area.