Replacing Pt catalysts with less expensive materials is of critical importance for the commercialization of fuel cells. Pd, which is comparable to Pt in the hydrogen oxidation reaction (HOR) activity and of which price is about one third of Pt, is employed as an anode catalyst. In a half cell or a single cell, the HOR activity of Pd can be enhanced by alloying other elements such as Ru. However, there is still a performance gap compared to the state-of-the-art PtRu and this gap can be closed by using a co-catalyst, tungsten oxide. When PdRu or PdIr is coupled with WON, there is a significant increase in cell performance, which indicates the promotion of HOR by WON. Although tungsten oxide itself does not have enough catalytic activity for HOR, it seems to act as a hydrogen-storage medium through the formation of hydrogen tungsten bronze, so called the H spillover effect, leading to the enhancement of HOR at Pd alloy surfaces. 2014 Elsevier B.V. All rights reserved.