EFFECT OF PLATINUM PARTICLE-SIZE ON THE OXYGEN REDUCTION REACTION ON 2-PERCENT PT-1-PERCENT H2WO4 IN PHOSPHORIC-ACID

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