Understanding the performance losses and “invasiveness” of in situ characterization steps during carbon corrosion experiments in polymer electrolyte membrane fuel cells

Abstract

Carbon corrosion represents one of the most critical degradation mechanisms within state-of-the-art polymer electrolyte membrane fuel cells. Its most prominent consequences include the loss of electrochemical active surface area (ECSA), porosity, and electrical contact within the electrode. The present study seeks a detailed understanding of the dependence between the polarization performance losses and the individual loss terms, both as a function of the amount of corroded carbon. A simplified onedimensional polarization model is developed with the aim to simulatively reconstruct the empirical polarization curve based on in situ cell characteristics during the course of carbon corrosion. It is shown that this model enables the assignment of nearly all voltage losses at various stages of the corrosion process, up to a cell current density of around 2A cm -2 . Furthermore, the "observer effect" during the carbon corrosion studies is investigated, where it is demonstrated that the application of characterization steps exerts strong adverse effects on the ECSA. This is explained by the "voltage cycling" conditions which are inevitably introduced during the characterization protocols, part of which is conducted under cell voltage as low as 0.2V.

Corrosion and Materials Degradation in Electrochemical Energy Storage and Conversion Devices

“…The C‐corrosion causes overall MEA degradation and severe PEMC performance decay attributed to the decrease in mass transport, collapse of the pore structure, loss of hydrophobicity, breakdown of catalyst connectivity, and reduced electrochemical active surface area (ECSA). The choking of the pore network by the carbon aggregates hinders mass transport [25,110–114] …”

“…Compared to the potential cycling AST, start/stop cycling is shown to cause substantial C‐corrosion [118–123] . The measurement of actual carbon loss and the evaluation of PEMC performance degradation (current density reduction and ECSA loss) were typically followed in the different AST protocols [112,121,124] . Distribution of relaxation time (DRT) investigation showed that the degradation behaviours vary with the type of AST used.…”

“…Instead, the potential holding test at 1.4 V caused a severe R ct increase with the positive shift of specific relaxation time, owing to the porous electrode's structural deformation and the formation of oxygen‐functional groups [125] . Figure 8 shows cross‐section SEM micrographs of MEA after five corrosion cycles (carbon loss ∼40 wt %), where the formation of Pt bands in the membrane due to the Pt migration and detachment due to C‐corrosion can be seen (evident in the zoomed‐in image) [112] …”

“…C‐corrosion under the rim was less severe than under the flow channel due to the comparably lower accessibility to the oxygen and water vapour under the rim [111] . Several recent works employed various modelling methodologies to study C‐corrosion [112,145,149–151] …”

Evaluation of functional layers thinning of high temperature polymer electrolyte membrane fuel cells after long term operation

“…[15][16][17][18] In other studies, the whole membrane electrode assembly (MEA) is studied after applying some sort of accelerated stress test (ASTs). [19][20][21][22] Thus, not many studies analyse PEMFC degradation after operation in realistic conditions for thousands of hours. 23 Furthermore, in these long-term studies, the inhomogeneities in the degradation process (e.g.…”