Experimental investigation on dynamic characteristics of proton exchange membrane fuel cells at subzero temperatures

• The voltage response is proportional to ambient temperature and current density.
• There exists a time constant for the response to be stable.
• The initial membrane water content is beneficial to the cell performance.

Cold start and operation of a proton exchange membrane fuel cell (PEMFC) at the cold temperatures are crucial to the commercialization of it in the field of transportation. A 32 cm2 two cell stack is prepared to conduct the experiments at subzero temperatures, including cold start processes and cell performance testing, aiming of the characteristics of the cell. The startup study under subfreezing temperatures is conducted by galvanostatic method at various operation conditions, i.e. ambient temperature (−3 and −5 °C), current density and anode stoichiometry. The results show that the voltage evolutions are proportional to the operating current densities under the former two conditions, but the relationship becomes the opposite at the last condition. It is also found that the time constant for the cell to reach steady status is no more than 100 s and highly depends on the startup mode. In addition, the performance of the cell is tested at the temperature of 0 °C and −3 °C. The comparison of pre-humidification and normal operations indicate that the initial water content of membrane affects the cell performance.