مکانیک هوافضا (Apr 2023)
Experimental Investigation of the Effect of Cathode Side Liquid Water Accumulation on the Impedance of a Dead Ended Polymer Electrolyte Membrane Fuel Cell by Electrochemical Impedance Spectroscopy Method
Abstract
Polymer electrolyte membrane fuel cells with dead-end mode operation are known as an important alternative for achieving a clean and sustainable future in terms of energy supply for the transportation sector, as well as for military and aerospace applications. Their commercial success, however, is dependent on addressing the water management issue that accumulates inside their channels and porous media during dead-end operations. The current work utilized the electrochemical impedance spectroscopy method to evaluate the effect of gradual accumulation of liquid water in the cathode on the impedance diagram of a dead-end fuel cell. Despite the fact that this approach is limited to steady-state systems and dead-end operation is transient, quasi-steady conditions were provided for the test by measuring the impedance of each frequency in a distinct dead-end interval. Furthermore, the effect of relative humidity, operating temperature, and inlet pressure of reacting gases on the impedance of a dead-end fuel cell was examined. The results show that in such a situation, a large amount of water is always present in the fuel cell, which, while it helps to keep the membrane hydrated and reduces ohmic resistance, causes difficulty in the transport of reacting gases (particularly oxygen) to the catalyst layer, increasing mass transport resistance. Moreover, flooding the catalyst layer reduces the kinetics of the reaction and, as a consequence, increases the charge transfer resistance. Therefore, it is required to specify a criterion for the opening time of the purge valve by considering a threshold for the acceptable value of the cell's total resistance to prevent excessive voltage drop, which is the subject of the next step of this research.
