The Effect of Potential Cycling on High Temperature PEM Fuel Cell with Different Flow Field Designs

Abstract

Degradation of phosphoric acid doped polybenzimidazole membrane based fuel cells under accelerated potential cycling conditions is investigated in current study. Three unit cells with identical high temperature membrane electrode assembly were assembled with three different cathode flow field designs. The fuel cell is cycled between 0.5 V and 0.9 V with 3 min dwelling time for each voltage set point. Performance degradation mechanisms associated with differences in cathode flow design are identified. The fuel cell with multiple serpentine design is operated for a maximum of 4,821 potential cycles with only 38.6% of initial performance remaining at the end‐of‐test (EoT), whereas straight and parallel design operated for only 3,188 cycles. The electrochemical characterization studies reveal the cause of observed performance losses from polarization curves. Irrespective of the design type used there are very high activation losses observed which accelerated with accelerated stress tests (AST) testing. The impedance studies reveal high charge transfer resistance related to increased platinum crystal growth on cathode and reduced electrochemical surface area (ECSA) of catalyst. Overall the AST results in irreversible performance loss and severe degradation of the cathode catalyst support and catalyst itself.

Challenges and opportunities for characterisation of high-temperature polymer electrolyte membrane fuel cells: a review

“…This is due to the established dependence of catalyst degradation mechanisms on potential. Carbon corrosion is typically targeted using cycling with upper limits >1.0 V, whereas Pt degradation mechanisms can be targeted with slightly lower limits ∼0.9 V. 122,551,552 Potential cycling ASTs oen operate with H 2 and N 2 supplied to the anode and cathode, respectively, to avoid superimposed currents caused by the oxidation of hydrogen interfering with corrosion current measurements. 156 Many AST studies targeting catalyst degradation in HT-PEMFCs use dry gases as would be typical in normal operation; however, unlike during operation, these ASTs result in no water at the cathode during cycling which has a signicant effect on recorded degradation; humidied conditions can lead to irreversible degradation, whereas performance was reported to be recoverable aer operating in dry conditions as the dehydrationrestricted Pt dissolution mechanisms that require ion conductivity involve reaction with water.…”

An overview of flow cell architecture design and optimization for electrochemical CO2 reduction

“…5d-5f). [56][57] These studies also emphasized the importance of proper flow field design for long-term operation under adverse conditions.…”

“…The above data suggest that the optimization of the flow rate greatly affects the CO2RR performance, including the current density, FE, and product distribution. 56 Copyright 2019, Wiley-VCH. (g) Polarization curves and (h) FEs at different gas flow rates of CO2.…”

“…Flow field designs investigated (d) multiple serpentine, (e) segmented serpentine and (f) straight and parallel. Reproduced with permission 56. Copyright 2019, Wiley-VCH.…”

Modeling the Performance Degradation of a High-Temperature PEM Fuel Cell

“…One major drawback compared to low-temperature PEM fuel cells (LT-PEMFC) is the accelerated degradation as a result of the higher operating temperatures. It is also known that HT-PEMFCs degrade faster under cycling operation modes, such as load cycling [12], potential cycling [13], thermal cycling and start/stop cycling, which can exacerbate the degradation of an HT-PEMFC [12,14]. However, cycling is also detrimental to LT-PEMFCs.…”