The catalytic activity of Pt nanoparticles supported by zeolite-type mesoporous Cs 2.5 H 0.5 PW 12 O 40 solid super-acid towards oxygen reduction has been explored. Pt(IV) impregnated Cs 2.5 H 0.5 PW 12 O 40 was prepared by titration of an aqueous solution of phosphotungstic acid and a known quantity of H 2 PtCl 6 with a solution of cesium carbonate. The H 2 PtCl 6 impregnated insoluble salt was subsequently chemically or electrochemically reduced to form supported Pt nanoparticles.HRTEM micrographs show that the reduced composites Pt–Cs 2.5 H 0.5 PW 12 O 40 (Pt–Cs 2.5 PW 12 ) contains Pt nanoparticles of average dimensions 2–5nm, embedded into the porous structure of the insoluble salt. RDE and RRDE studies and fuel cell polarization data performed using thin layer composite films of Pt–Cs 2.5 PW 12 chemically or electrochemically reduced show that the catalyst is very stable and rather efficient for oxygen reduction (ORR). The oxygen reduction wave is shifted by 60–70mV towards more positive potentials with respect to the one obtained using electrodes prepared with a standard catalyst such as E-Tek 20% Pt–Vulcan. Analysis of the voltammetric curves demonstrates that the electrocatalytic activity of the composite electrodes is higher than that of the standard catalyst. This indicates that the solid state super-acid Cs 2.5 H 0.5 PW 12 O 40 acts as co-catalyst by providing a proton rich environment in the vicinity of the Pt nanoparticles that enhances their catalytic activity towards oxygen reduction.
