A 2% Pt-1% H2WO4-based electrocatalyst has been fabricated by an inexpensive chemical route for use as an oxygen cathode in 99% phosphoric acid at 180 degrees C. The effect of the platinum particle size on the electrode performance for the oxygen reduction reaction (ORR) was studied. The electrocatalytic properties for the ORR, e.g., exchange current density, mass activity and specific activity of a 2% Pt-1% H2WO4-based electrode fabricated from 5% Pt, were found to be several times higher than those of 10% Pt-based electrocatalysts. It was shown that the performance of this electrode is not related to an increase in its electrochemically active surface area, but to its chemical composition. Based on the concept of synergistic process of the ORR on materials we have previously emphasized, it is shown that a 2% Pt-1% H2WO4-based electrocatalyst is a synergistic system due to an increase of the active sites at the electrocatalyst surface.