(Perspective)Deconvolution of the dehydration degradation mechanism in polymer electrolyte membrane fuel cells using electrochemical impedance analysis combined with the transmission line model under low humidity

Abstract

Herein, electrochemical impedance spectroscopy (EIS) analysis is performed under low-relative humidity conditions (RH30) to use the transmission line model (TLM) to emphasize ionic resistance in a polymer electrolyte membrane fuel cell (PEMFC). In particular, EIS measurement under RH30 based on the TLM (TLM-RH30) facilitates a focus on the inherent properties of the membrane electrode assembly (MEA) by deliberately limiting and separating the proton conductivity from the complicated impedance circuits. To verify the feasibility of TLMRH30 in EIS analysis, the dehydration degradation test of a PEMFC is performed under RH 30% for more than 600 h. From the electrochemical results obtained using TLM-RH30, the degradation mechanism can be sequentially deconvoluted with respect to operating time; (i) first, an increase in ionic resistance occurs, followed by (ii) membrane thinning and (iii) reverse current decay inducing severe cathode deterioration due to carbon corrosion. The sequential degradation mechanism under dehydration is also supported by the surface analysis results of deteriorated MEAs using SEM TEM, EDS, XRD, and XPS. It is notable that EIS analysis adopting TLMRH30 enable an accurate diagnosis by establishing the sequential degradation causes in each MEA component, such as the ionomer, membrane, and catalyst layer, in a PEMFC.