Neutron Imaging of An Enzyme Fuel Cell

Platinum is an expensive catalyst that increases the cost of polymer-electrolyte-membrane fuel cells (PEMFCs). In enzyme fuel cells (EFCs), enzymes instead of platinum are used to catalyze the electrochemical reactions. As is the case for PEMFCs, water management affects the performance of EFCs. Water is needed to be present for the enzymes to be active. In previous studies in our laboratory with a three-dimensional cathode EFC, it has been observed that the power output of the EFC was gradually lost. This behavior was attributed to either (i) loss of water in the enzymatic cathode or (ii) loss of enzymatic activity. An attempt was made to measure the water content of the cathode, but these measurements were intrusive to the EFC and interrupted its operation. Here, we employed neutron imaging, which is an ideal technique to in-situ study the water content of an operating fuel cell. Initial experiments verified the technique by introducing a known volume of enzyme solution into the cathode and then determining this volume using neutron imaging. Then, the effects of operating conditions such as feed humidity, feed flow rate, and enzyme solution composition were studied and compared with power output of the EFC. These experiments allowed the separation of contributions from mediator/enzyme decay and dehydration to output loss over time. Electrochemical impedance spectroscopy (EIS) studies were also performed on the EFC to provide a better understanding of how various operating parameters affected internal resistances.