PEMFC Stack Activation Through Thermal Management

Activation of PEM fuel cell stack is an important factor in setting peak power of stack before its steady operations. Several methods of activation for larger capacity stacks involve operation of the stacks initially at low voltages under highly humidified conditions and at high temperatures. This is expected to improve proton conductivity of the membrane. For large area cells this method can create hot spots due to high current and non-uniform temperature distribution. Hence, an alternative approach for activating PEMFC stack at low current for vehicular applications has been investigated in this study. Conventional stack activation requires continuous supply of coolant. However for vehicular applications, a closed loop thermal management system is required. During the course of developing such a close loop thermal management system for transportation application, we have identified that the same system can be used in activating a PEM fuel cell stack. In the present study a 5kW PEMFC stack, operating on dry reactants, has been activated using a closed loop thermal management system. The activation has been carried out over a period of 620 minutes with 6 start/stop cycles. Through the start stop cycles the power delivered by the stack steadily increased from 2.5kW, to 5kW. Further, heat developed inside the fuel cell, as removed by the coolant water, has been studied and there is a proportional increase in the overall heat removed by the coolant to the total power delivered by the fuel cell. The start stop cycles are regulated based on the single cell voltages and stack temperature. Each cycle is stopped when the stack temperature reaches a set temperature of 50°C. The advantage of this procedure is that it will result in long life of the fuel cell stack, uniform membrane equilibration, and will avert hot spot generation in the electrodes at low cell potential.