Evaluation of cathode contamination with Ca2+ in proton exchange membrane fuel cells

An ex-situ evaluation of the effects of Ca2+ on the cathode of proton exchange membrane fuel cells was completed. A Ca2+ concentration of 0.9 mM in the HClO4 solution had no effect on the oxygen reduction reaction activity of a Pt/C catalyst. Upon increasing the Ca2+ concentration to 9 and 90 mM, the availability of Pt active sites slightly decreased in the presence of Ca2+, and other observed effects included (i) a decrease in the kinetic and diffusion-limited currents; (ii) a decrease in the electron transfer number, and accordingly, an increase in H2O2 formation; and (iii) an increase in the acid site occupation and a decrease in the O2 permeability in the ionomer. The Ca2+ cations that were absorbed in the ionomer reduced the mass-transport kinetics of O2 and blocked the adsorption of O2 on the Pt particles.