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

Abstract

In analogy with W 2 N and WO 3 , WS 2 and WP were found to undergo the CH 4 carburization to produce α-WC. α-WC obtained from WS 2 and W 2 N exhibited a high specific surface area compared with other routes. The introduction of a small amount of Pt into the WCs prepared in these ways contributed to a remarkable activity enhancement for the hydrogen electro-oxidation reaction. Tungsten carbides (WC) with different crystalline phases prepared from WO 3 as the starting material showed electrocatalytic activity in the order of α-WC > β-WC 1− x > β-W 2 C for the hydrogen oxidation reaction. α-WC obtained by methane carburizing of tungsten nitride (W 2 N), which was prepared from nitridation of WO 3 , produced much higher surface area than that from the direct carburization of WO 3 . We first found capable of carburize tungsten sulfide (WS 2 ) and tungsten phosphide (WP) to produce α-WC though they require severe carburization reaction. In particular, α-WC obtained from WS 2 exhibited a high specific surface area as well as α-WC by way of W 2 N. The XPS analysis revealed that the surface properties of α-WC are significantly dependent on the preparative methods. A large amount of graphite carbon was deposited on the surface of α-WC from direct carburization, whereas, there was far less on α-WC by way of W 2 N and WS 2 .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 α-WC enhance the utilization of Pt for the hydrogen electro-oxidation reaction.