Effect of open circuit voltage on performance and degradation of high temperature PBI–H3PO4 fuel cells

The impact of open circuit voltage (OCV) on the performance and degradation of polybenzimidazole–phosphoric acid (PBI–H3PO4) fuel cells operated at 180 °C was investigated. The OCV showed an initial quick increase in the first few minutes, followed by a much slower increase, and peaked after about 35 min. It then started an exponential and monotonous decline. Along with the decline of OCV, the performance of the fuel cell also declined. Operating the fuel cell with a load of 0.2 A cm−2 could temporarily boost the OCV and the fuel cell performance, but it could not recover the lost performance permanently. Electrochemical impedance spectroscopy (EIS) indicated significant loss of catalyst activity and increase in mass transport resistance due to the relatively high potential at OCV. X-ray diffraction (XRD) measurement showed that the cathode Pt crystallite size increased by as much as 430% after a total of 244.5 h of exposure to OCV.