Chemical vapor deposition of tungsten carbide films on silicon and carbon substrates

Environmental and health concerns to reduce polluting emissions from combustion of fossil fuels, in addition to diminishing natural resources and the desire for sustainable development with renewable resources has driven the effort to develop fuel cell technology. In particular, there is an interest in the direct methanol fuel cell (DMFC) because of the desire to have an alternative fuel to hydrogen---the fuel used in all other fuel cells---especially for automobile and portable electronics applications. The current anode catalyst in the DMFC is a Pt/Ru alloy, which in addition to being expensive requires high loadings and is susceptible to carbon monoxide (CO) poisoning. The need to investigate alternative anode catalysts is the motivation behind the current work. Tungsten carbide has been identified as a potential alternative catalyst because of platinum-like behavior, chemical stability in acidic solution and resistance to CO poisoning.; In the present work, chemical vapor deposition was used to deposit tungsten carbide from a mixture of WCl6, H2 and C3H 8 at 750--1050°C on silicon and carbon substrates. The phase composition of the films was correlated with substrate temperature, substrate position in the reactor, and total flow rates. X-ray diffraction and X-ray photoelectron spectroscopy were employed to investigate the surface and bulk properties of the thin films. Thick, adherent films of phase-rich hexagonal WC were deposited using 10 Torr total pressure, 1050°C substrate temperature, and reactant flow rates of H2/C3H8/Ar/WCl 6 = 1.8x10-2/3.6x10-3/8.9x10 -4/1.8x10-4 x moles/min, where Ar is the carrier gas. The surface composition was oxygen and carbon rich as compared with the bulk.