Characteristics of proton exchange membrane fuel cells cold start with silica in cathode catalyst layers

In this study, a novel strategy is reported to improve the cold start performance of proton exchange membrane (PEM) fuel cells at subzero temperatures. Hydrophilic nano-oxide such as SiO2 is added into the catalyst layer (CL) of the cathode to increase its water storing capacity. To investigate the effect of nanosized SiO2 addition, the catalyst coated membranes (CCMs) with 5 wt.% and without nanosized SiO2 are fabricated. Although at normal operation conditions the cell performance with nanosized SiO2 was not so good as that without SiO2, cold start experiments at −8 °C showed that the former could start and run even at 100 mA cm−2 for about 25 min and latter failed very shortly. Even at −10 °C, the addition of SiO2 dramatically increased the running time before the cell voltage dropped to zero. These results further experimentally proved the cold start process was strongly related with the cathode water storage capacity. Also, the performance degradation during 8 cold start cycles was evaluated through polarization curves, cyclic voltammetry (CV) and electrochemical impedance spetra (EIS). Compared with the cell without SiO2 addition, the cell with 5 wt.% SiO2 indicated no obvious degradation on cell performance, electrochemical active surface area and charge transfer resistance after experiencing cold start cycles at −8 °C.