Anodic oxidation of formic acid on PdAuIr/C-Sb₂O₅·SnO₂ electrocatalysts prepared by borohydride reduction

PdAuIr/C-Sb₂O₅·SnO₂ electrocatalysts with Pd:Au:Ir molar ratios of 90:5:5, 70:20:10 and 50:45:5 were prepared by borohydride reduction method. These electrocatalysts were characterized by EDX, X-ray diffraction, transmission electron microscopy and the catalytic activity toward formic acid electro-oxidation in acid medium investigated by cyclic voltammetry (CV), chroamperometry (CA) and tests on direct formic acid fuel cell (DFAFC) at 100℃. X-ray diffractograms of PdAuIr/C-Sb₂O₅·SnO₂ electrocatalysts showed the presence of Pd fcc phase, Pd-Au fcc alloys, carbon and ATO phases, while Ir phases were not observed. TEM micrographs and histograms indicated that the nanoparticles were not well dispersed on the support and some agglomerates. The cyclic voltammetry and chroamperometry studies showed that PdAuIr/C-Sb₂O₅·SnO₂ (50:45:5) had superior performance toward formic acid electro-oxidation at 25℃ compared to PdAuIr/C-Sb₂O₅·SnO₂ (70:20:10), PdAuIr/C-Sb₂O₅·SnO₂ (90:5:5) and Pd/C-Sb₂O₅·SnO₂ electrocatalysts. The experiments in a single DFAFC also showed that all PdAuIr/C-Sb₂O₅·SnO₂ electrocatalysts exhibited higher performance for formic acid oxidation in comparison with Pd/C-Sb₂O₅·SnO₂ electrocatalysts, however PdAuIr/C-Sb₂O₅·SnO₂ (90:5:5) had superior performance. These results indicated that the addition of Au and Ir to Pd favor the electro-oxidation of formic acid, which could be attributed to the bifunctional mechanism (the presence of ATO, Au and Ir oxides species) associated to the electronic effect (Pd-Au fcc alloys).