Effects of cell and electrode design on the CO tolerance of polymer electrolyte fuel cells

Abstract

Injection of low levels of oxygen or air, in the order of 1–5%, into the fuel stream is a popular method to obtain full CO tolerance to 100 ppm or more, in polymer electrolyte fuel cells (PEFC) operating on reformed, i.e. CO contaminated fuel. The susceptibility of the fuel cell towards this “O₂ bleeding” technique was investigated with a focus on cell design and electrode structure effects. Two different cell constructions were explored, a one-dimensional (1-D) cell with homogeneous gas distribution over the active area, and a two-dimensional (2-D) cell with a gas channel flow field. It was found that if Pt–Ru is used as anode electrocatalyst instead of Pt, less oxygen in the fuel stream is required to achieve full tolerance to 100 ppm CO in H₂. In the 2-D cell hardware, oxygen bleeding was less effective, probably due to shorter contact time. By using a bilayer anode, comprising a gas phase catalyst layer, it was possible to promote in situ catalytic CO oxidation, reducing thereby CO poisoning of the electrocatalyst and increasing the susceptibility towards O₂ bleeding in the 2-D cell.