Electrochemical characterization of a polybenzimidazole-based high temperature proton exchange membrane unit cell

In-Situ Dynamic Characterization of Energy Storage and Conversion Systems

“…It usually appears as the largest semi-circle in Nyquist plot and spans from 100 Hz to 1 Hz [68,78,79,[81][82][83][84]. A consistent interpretation proposed for this arc were widely accepted in published cases that an activation process related to ORR contributed to this polarization loss.…”

“…But, inconsistent with these results, many other researchers reported an increase of RΩ with increasing temperature when the temperature went higher than around 140ºC [73,80,82].…”

“…Later, it was confirmed in many other experiments that RΩ decreases with increasing current density [77,[79][80][81][82]. Following Zhang's theory [79], it was accepted that the decrease of RΩ was resulted from an increase in the proton conductivity of the membrane due to higher water productivity at higher current density.…”

“…It dominates the region of frequency from above 100 Hz up to 1000 Hz [68,78,79,[81][82][83][84], or even higher. The effects of temperature [79,82] and current density [81,82] on this impedance arc are observable but not as significant as on other impedance arcs dominating lower frequency regions. The resistance of this HF impedance arc decreases with increasing current densities, and its time constant decreases with increasing temperature.…”

“…Many researchers preferred to ascribe this HF arc to the charge transfer process occurring on the anode, that was the charge transfer process involved in hydrogen oxidation reaction (HOR) [73,77,78,80]. Some other groups stated that the charge transfer processes of both HOR and ORR contributed to this HF impedance arc; however, the contribution of HOR was negligible at low current density [79,82].…”