The specific activity, i(sp)/A m(-2) (current density per real surface area
), of Cl-free well-homogenized Pt-Ru particles at 25 and 60 degreesC in aqu
eous acidic solutions has been found to decrease with a decrease in the siz
e of the Pt-Ru alloy particles, and the mass activity, i(mass)/A g(-1) (cur
rent density per mass of catalyst metal loaded), showed the same dependency
when the size of the alloy particles was < ca. 3 nm in diameter.