Improvements in electrical and electrochemical properties of Nb-doped SnO2−δ supports for fuel cell cathodes due to aggregation and Pt loading

Abstract

We found that Nb-doped SnO_2−δ nanoparticles were improved in their electrical conductivity by more than two orders of magnitude by the aggregation of the particles, including the fusion of nearest-neighbor particles to form a random branching structure, and the formation of a porous agglomerated structure similar to that of conventional carbon blacks. The electrical conductivity was increased by an additional two orders of magnitude as a result of the loading of Pt nanoparticles to produce an electrocatalyst (Pt/Nb-doped SnO_2−δ) for fuel cell applications. We also found that the specific activities of Pt/Sn_0.96Nb_0.04O_2−δ (16 wt% Pt loading) for the oxygen reduction reaction increased with increasing electrical conductivity of the support and exceeded that of a conventional Pt catalyst supported on carbon black (Pt/CB). Since the tin oxide supports are much more stable than CB supports to the exposure to positive potentials (0.9 ∼ 1.3 V) during the start/stop operation of fuel cells, Pt or Pt alloy catalysts supported on oxide supports with such a chain-like, necked structure, as developed in this work, become superior candidates as robust cathode catalysts for the fuel cell vehicle application.