Hydrogen insertion in substoichiometric titanium carbide

Titanium carbide allows the insertion of hydrogen inside its structure, but only under two conditions. First, the carbide must be as substoichiometric as possible, i.e. close to TiC0.60, because hydrogen requires the presence of carbon vacancies to penetrate the carbide. Second, the carbon vacancies must be ordered, leaving the (111) planes as empty as possible. The corresponding ordered structure is trigonal (space group R-3m). The other carbide structures (disordered Fm-3m NaCl type, or ordered Pd-3m) allow only little hydrogen insertion. Experimentally, samples of different stoichiometries were tested; they were obtained by reactive sintering of mixtures TiC0.98 +Ti at 2100 degrees C, which gave the disordered structure Fm-3m. The trigonal structure was obtained from the disordered one, utilising a 40 h annealing treatment in argon at 730 degrees C. Longer treatments favored the structure Fd-3m. Hydrogen was inserted electrochemically, but other methods to achieve this result could exist. The interest of substoichiometric TIC. lies in its low density, its chemical inertia and its cost, cheaper than noble metals. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.