Synthesis and characterization of high-surface area tungsten carbides and application to electrocatalytic hydrogen oxidation

Tungsten carbides (WC) with different crystalline phases prepared from WO3 as the starting material showed electrocatalytic activity in the order of alpha-WC > beta-WC1-x > beta-W2C for the hydrogen oxidation reaction. a-WC obtained by methane carburizing of tungsten nitride (W2N), which was prepared from nitridation of WO3, produced much higher surface area than that from the direct carburization of WO3. We first found capable of carburize tungsten sulfide (WS2) and tungsten phosphide (WP) to produce a-WC though they require severe carburization reaction. In particular, alpha-WC obtained from WS2 exhibited a high specific surface area as well as a-WC by way of W2N. The XPS analysis revealed that the surface properties of alpha-WC are significantly dependent on the preparative methods. A large amount of graphite carbon was deposited on the surface of alpha-WC from direct carburization, whereas, there was far less on alpha-WC by way of W2N and WS2. The electrocatalytic activities of WCs obtained in these ways were greatly improved. The binary catalysts of WC promoted with Pt were evaluated in comparison with the current Pt catalyst. The introduction of a small amount of Pt onto the WC contributed to a remarkable anodic current enhancement. It turned out that the specific activity (activity based on the surface area of Pt metal) was higher than that of the commercial catalyst. It is concluded that the interaction Pt with alpha-WC enhance the utilization of Pt for the hydrogen electro-oxidation reaction. (C) 2007 Elsevier B.V. All rights reserved.