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Abstract  An electrocatalytic system that utilizes tungsten oxide modified carbon-supported RuSex nanoparticles is developed and characterized here using transmission electron microscopy and such electrochemical diagnostic techniques as cyclic voltammetry and rotating ring-disk voltammetry, as well as upon its introduction (as cathode) to the low-temperature hydrogen–oxygen fuel cell. After the modification of RuSex catalytic centers with ultra-thin films of WO3, the potential of oxygen reduction in 0.5 mol dm−3 H2SO4 (in the absence and presence of methanol) is shifted ca. 70 mV (under rotating disk voltammetric conditions) towards more positive values, and the percent formation (at ring) of the undesirable hydrogen peroxide has decreased approximately twice when compared to the WO3-free system. Relative to bare electrocatalyst, an increase of power density from 75 to 100 mW cm−2 (at 300 mA cm−2) has been observed upon utilization of WO3-modified RuSex in polymer electrolyte membrane fuel cell at 80 C. In comparison to Vulcan-supported Pt nanoparticles, the overall electrocatalytic performance of tungsten oxide modified carbon-supported RuSex nanoparticles is lower, but the latter system is practically insensitive to the presence of methanol even at 0.5 mol dm−3 level. [ABSTRACT FROM AUTHOR]