In situ Mössbauer spectroscopy on an operating fuel cell

In situ Mössbauer spectroscopy has been utilized to examine an operating high surface area carbon oxygen-fed cathode with preadsorbed iron phthalocyanine (FePc) in alkaline solution. The configuration used was essentially that of a fuel cell with a hydrogen fed electrode as the anode. The results indicated that the isomer shift and quadrupole splitting observed at -200 mV vs. Hg/HgO, OH^- during O₂ reduction are the same as those obtained at open circuit in the absence of O₂ and correspond to adsorbed FePc presumably at monolayer coverages. At higher overpotentials (∼ -300 mV vs Hg/HgO, OH^-), however, a fraction of the catalyst is either demetallated or otherwise irreversibly desorbed from the carbon surface, as judged from the observed decrease in the total resonant absorption area. Polarization measurements for reduction of O₂ in 4 M NaOH at 60°C with gas-fed high surface area carbon electrodes have indicated that the catalytic activity is increased over that of the carbon alone by adsorbed FePc. The activity is even more enhanced, however, by the presence of crystalline FePc in the porous electrode.