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

Abstract

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, 37m2g−1; Pt loading, 10.0wt%) and Sn0.96Sb0.04O2–δ (Pt/Sn0.96Sb0.04O2–δ; BET area of support, 33m2g−1; Pt loading, 12.3wt%), 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 79.7m2g−1 (Pt/Sn0.96Nb0.04O2–δ) and 68.6 m2g−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 0.4V. For operating potentials below 0.4V, 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.