Experimental Study on Transient Response Characteristics of Commercial-Size PEMFC under Varying Load

Proton exchange membrane fuel cell (PEMFC) is a promising next-generation energy conversion device. The response characteristics of mass transfer and electrochemical reactions during a transient process affect the cell performance and still require further investigation. Experiment is conducted to measure current density distribution under varying load and reactant flow rate in a commercial-size single cell. Local current density around cathode inlet is higher in normal operating conditions due to higher local oxygen concentration. Such area performs a better transient response when a step change of load current is demanded leading to much larger current density at cathode inlet and lower at outlet. The redistribution of reactant gas concentration in a commercial-size fuel cell happens after the load change and takes a few seconds. After the redistribution a balance is reached and current density distribution tends to get more homogeneous with lower performance at cathode inlet and higher at outlet. Inhomogeneous current density distribution indicates inadequate use of catalyst and more energy dissipated caused by in-plane potential difference. Cell voltage and the overall cell performance has a negative linear correlation with the inhomogeneity of local current density during a transient process when fuel cell is supplied with more reactant gas or has a higher load current demand while keeping the gas flow constant. This work leads to suggestion on flow control strategy during dynamic load demands. The results also lay a foundation for further study into the design of flow channel in the fuel cell for better transient response characteristics and wider application conditions.