The Impact of Carbon Stability on PEM Fuel Cell Startup and Shutdown Voltage Degradation

Abstract

Conventional carbon MEAs and graphitized carbon MEAs were evaluated for the resistance to carbon corrosion and startup/shutdown durability in this paper. Graphitized carbon MEAs show higher resistance to carbon corrosion than conventional carbon MEAs by a factor of 35 at a point where 5% weight loss had occurred. A graphitized carbon MEA yielded lower degradation rate than that of a conventional carbon MEA by a factor of 5 after 1,000 startup/shutdown cycles. The kinetics of carbon corrosion over both conventional carbon MEAs and graphitized carbon MEAs were measured, and carbon corrosion during startup/shutdown was explained and modeled. The model results correlate to what we have measured from our startup/shutdown durability test. Overall, MEAs with corrosion resistant carbon supports are one of major materials approaches to mitigate cell voltage degradation due to fuel cell startup/shutdown. We believe that a combination of corrosion resistant materials and system operating mitigation strategies is the path to attain the strict automotive durability targets.

Start/Stop and Local H2 Starvation Mechanisms of Carbon Corrosion: Model vs. Experiment

“…Consequently, since graphitized carbon-supports have lower carbon corrosion rates, the use of cathode catalysts with graphitized supports significantly reduces H 2 /air-front start/stop damage (3). Furthermore, if the oxygen reduction reaction activity of the anode electrode is reduced by lowering the anode Pt loading, the H 2 /air-front start/stop degradation is decreased (4). This is consistent with a kinetic H 2 /air-front start/stop model, where the O 2 reduction current on the anode electrode is balanced by carbon-support oxidation and O 2 evolution on the opposing cathode electrode side (3,6).…”

“…Previously, we have successfully modeled the start/stop process via a steady-state analysis in which we took the H 2 /air-front at the middle of the flow path to be representative of the average carbon corrosion rate and neglected the electrode's pseudo-capacitive effects (3). The model results agree well with experimental data from accelerated H 2 /air-front start/stop experiments, in which long H 2 /air-front residence times are used to accelerate the evaluation of MEA materials/design impact start/stop degradation rates (3)(4). To date, Figure 1 represents the carbon corrosion mechanism considered in all start/stop and local H 2 starvation models (3,(8)(9)(10).…”

Spatially Resolved Electrode Diagnostic Technique for Fuel Cell Applications

“…Good agreement is seen between the limiting current and cathode thickness measurement results as functions of aging time. Additionally, the general time dependence that is observed agrees with that reported for an earlier corrosion study (20). …”

Investigation of Carbon Loss on the Cathode during PEMFC Operation

“…The relationship between carbon loss and cell performance was confirmed by P. T. Yu et al (1). Several wt% carbon loss will cause a large voltage drop under FC operation.…”