Enhanced Durability of Pt/C Electrocatalysts with Protective Porous Niobium Oxide Nanocoatings

Platinum catalysts degrade through dissolution and growth in electrocatalytic reactions. This work attempted to make a protection nanocoating of porous niobium oxide (NbO x ) on Pt supported on carbon black (Pt/C), or Pt/C@NbO x , using the condensed layer deposition (CLD) technique. It was found that nanocoating thicknesses have a significant effect on the catalyst durability. The best catalyst was found to have a 29 wt% NbO x loading, corresponding to ca . 1.5 nm nanocoating thickness on the Pt/C catalyst. It was further found that thermal annealing critically influenced the catalyst performances. The Pt/C@NbO x catalyst annealed at 400 °C retained amorphous NbO x , while that annealed at 600 °C formed crystalline structures of NbO x . Electronic interactions between Pt and the crystalline NbO x were evidenced by Pt 4 f core electron binding energy shifting positively and Nb 3 d core electron shifting negatively. Accelerated stress tests for up to 30,000 cycles showed 16.5% increase in the electrochemical surface area (ECSA) of Pt/C@NbO x annealed at 600 °C, in contrast to a 49.8% loss in ECSA of Pt/C. More significantly, the loss in half-wave potential in oxygen reduction reaction is close to zero. This remarkably enhanced catalyst durability is attributed to the protection effect from the porous NbO x nanocoatings.