Characterization of Pt catalysts on Nb-doped and Sb-doped SnO2-δ support materials with aggregated structure by rotating disk electrode and fuel cell measurements

We found high activity and durability for oxide-supported Pt catalysts for the oxygen reduction reaction (ORR). These catalysts were supported on Sn0.96Nb0.04O2-δ (Pt/Sn0.96Nb0.04O2-δ; BET area of support, 37 m2 g−1; Pt loading, 10.0 wt%) and Sn0.96Sb0.04O2-δ (Pt/Sn0.96Sb0.04O2-δ; BET area of support, 33 m2 g−1; Pt loading, 12.3 wt%), by use of the rotating disk electrode (RDE) technique, and measured the I-E performance of single H2-air polymer electrolyte fuel cells (PEFCs) using these catalysts as the cathode. The nanoparticulate supports Sn0.96Nb0.04O2-δ and Sn0.96Sb0.04O2-δ had an aggregated structure similar to that of carbon black (CB). The electrochemically active surface area of Pt, estimated by cyclic voltammetry measurements with the RDE, reached 79.7 m2 g−1 (Pt/Sn0.96Nb0.04O2-δ) and 68.6 m2 g−1 (Pt/Sn0.96Sb0.04O2-δ). The ORR activity of Pt/Sn0.96Nb0.04O2-δ exceeded that of a commercialized Pt catalyst supported carbon black (Pt/CB). Higher durability was confirmed for Pt/Sn0.96Nb0.04O2-δ and Pt/Sn0.96Sb0.04O2-δ compared to that of Pt/CB with a test protocol for start/stop cycling recommended by the Fuel Cell Commercialization Conference of Japan (FCCJ) [1]. Single cells using these catalysts showed I-E performance superior to that for the Pt/CB at operating potentials above 0.4 V. For operating potentials below 0.4 V, a slight amount of Sn dissolution from the Sn0.96Sb0.04O2-δ support occurred, resulting in degradation of the cell performance due to Pt poisoning by Sn re-deposition, but no noticeable degradation at Sn0.96Nb0.04O2-δ was found, due to the suppressed Sn dissolution.