Fabrication and Performance of Membrane Electrode Assembly Using a Hydrophilic Pt/[TaOPO4/VC] Electrocatalyst

Abstract

Oxide- and phosphate-supported catalysts promote the oxygen reduction reaction (ORR) in acid and alkaline electrolyte. We previously reported a high mass- and area-specific ORR activity for an electrocatalyst with 18 wt% loading of 2.4 nm Pt nanoparticles supported on a 3 wt% tantalum oxyphosphate-treated VC (Pt/[TaOPO4/VC]). The electrocatalyst was heat treated at 660◦C in a reducing atmosphere and characterized using thin-film rotating disc electrode (RDE) in an acidic electrolyte and alkaline electrolyte. However preliminary experiments show that the performance of the Pt-TaOPO4 catalysts as measured by RDE is not representative of its performance in a proton exchange membrane fuel cell (PEMFC), possibly because of the hydrophilicity of the oxyphosphate. We reconcile the difference between RDE and PEMFC performance by developing a range of catalyst layers (CLs) fabricated by decal method and by direct deposition of the Pt/[TaOPO4/VC] electrocatalyst onto the Nafion® membranes using an in-house built ultrasonic spray coating system. Nitrogen adsorption, mercury porosimetry, and scanning electron microscopy (SEM) are used to investigate the effects of ionomer/carbon ratio (I/C) on the surface area, pore structure and morphology of the CLs; cyclic voltammetry and polarization curves are used to determine the electrochemically active area (ECSA) and PEMFC performance.