PEFC Electrocatalysts Supported on Nb-SnO2 for MEAs with High Activity and Durability: Part I. Application of Different Carbon Fillers

Abstract

Currently, carbon black is widely used as an electrocatalyst support for polymer electrolyte fuel cells (PEFCs). However, electrochemical oxidation leads to degradation of this material. In contrast, tin oxide (SnO2) is electrochemically stable even under strongly acidic conditions, and relatively high electronic conductivity can be achieved by doping with niobium (Nb-SnO2), compared with other metal oxides. In this study, Nb-SnO2 is composited with various conductive carbon fillers, including vapor-grown carbon fibers (VGCF), carbon nanotubes (CNT), and graphitized carbon black (GCB), followed by platinum nanoparticle decoration. These nanocomposite electrocatalysts are incorporated into membrane electrode assemblies (MEAs) and tested under PEFC operational conditions. The resulting fuel cells achieve high initial I-V performance up to 0.742 V at 0.2 A cm−2 (80°C), as well as excellent cycling durability. In particular, MEAs fabricated with Pt/Nb-SnO2/VGCF cathode electrocatalysts exhibit remarkable durability, with only a 12.1% drop in cell voltage at 0.2 A cm−2 over 60,000 start-stop cycles, and a 42.9% drop over 400,000 load potential cycles, corresponding to the lifetime of a fuel cell vehicle (FCV). Platinum-decorated metal oxide electrocatalysts can simultaneously realize high catalytic activity and extended durability, not only in ex-situ half-cell measurements, but also in full cell conditions.