Tom Mason

Water management and flooding play an important role in the performance and durability of polymer electrolyte fuel cells (PEFCs). In this study, a dynamic electro-mechanical analysis is performed to examine the performance of a working PEFC during hydration transients and flooding events. Cell resistance is measured using electrochemical impedance spectroscopy (EIS), and the stress/strain characteristics – cell compression and membrane electrode assembly (MEA) dimensional change – are studied… Show more

Water management and flooding play an important role in the performance and durability of polymer electrolyte fuel cells (PEFCs). In this study, a dynamic electro-mechanical analysis is performed to examine the performance of a working PEFC during hydration transients and flooding events. Cell resistance is measured using electrochemical impedance spectroscopy (EIS), and the stress/strain characteristics – cell compression and membrane electrode assembly (MEA) dimensional change – are studied using a controlled compression unit (CCU).

Ex-situ measurements of membrane thickness as a function of hydration level provide a direct correlation between ionic conductivity and thickness. During initial hydration of Nafion membranes there is a direct relationship between membrane conductivity and dimensional change (swelling) of MEAs. Electrode flooding is found to result in membrane hydration and an increase in stress or strain, depending on the compression mode of the fuel cell. Results suggest that hydration cycles and flooding events can lead to cell degradation due to the stresses imposed. Show less

A novel bulk acoustic wave (BAW) microgravimetric sensor based on gallium orthophosphate is demonstrated that it is capable of operation at high temperature (up to 900 °C). The sensor is applied to the detection of carbon deposition onto electrodeposited nickel from dry methane at 600 °C and used as an analogue for studying the coking of solid oxide fuel cell (SOFC) anodes. The degradation of electrochemical performance due to deposition of carbon onto symmetrical SOFCs with nickel/gadolinium… Show more

A novel bulk acoustic wave (BAW) microgravimetric sensor based on gallium orthophosphate is demonstrated that it is capable of operation at high temperature (up to 900 °C). The sensor is applied to the detection of carbon deposition onto electrodeposited nickel from dry methane at 600 °C and used as an analogue for studying the coking of solid oxide fuel cell (SOFC) anodes. The degradation of electrochemical performance due to deposition of carbon onto symmetrical SOFCs with nickel/gadolinium doped ceria electrodes is measured using electrochemical impedance spectroscopy (EIS). Direct correlation is observed between the frequency shift of the sensor and the change in resistance to charge transfer of the SOFC anode. An induction period (∼2 h) following exposure to methane is observed where no significant carbon deposition occurs. Show less

Compression plays an important role in the performance of polymer electrolyte fuel cells (PEFCs). In this study, dynamic compression is applied using a cell compression unit (CCU) to study the effect on performance of a membrane electrode assembly (MEA) with dimension change. The stress/strain characteristics of the MEA are observed to be dominated by the gas diffusion layer (GDL), with the GDL exhibiting a degree of plasticity. Electrochemical impedance spectroscopy (EIS) is used to delineate… Show more

Compression plays an important role in the performance of polymer electrolyte fuel cells (PEFCs). In this study, dynamic compression is applied using a cell compression unit (CCU) to study the effect on performance of a membrane electrode assembly (MEA) with dimension change. The stress/strain characteristics of the MEA are observed to be dominated by the gas diffusion layer (GDL), with the GDL exhibiting a degree of plasticity. Electrochemical impedance spectroscopy (EIS) is used to delineate the effect of compression on contact resistance and mass transfer losses.

With increasing compression, a significant reduction in net performance is observed, with the most significant differences occurring in the mass transport regions of the performance curves. As the compression increases, the high-frequency resistance reduces with the improvement in contact resistance between the GDL and bipolar plate material, concurrently the low frequency resistance increases with increasing compression. Show less

This paper describes the use of an in situ analytical technique based on simultaneous displacement and resistance measurement of gas diffusion layers (GDLs) used in polymer electrolyte fuel cells (PEFCs), when exposed to varying compaction pressure. In terms of the losses within fuel cells, the ohmic loss makes up a significant portion. Of this loss, the contact resistance between the GDL and the bipolar plate (BPP) is an important constituent. By analysing the change in thickness and ohmic… Show more

This paper describes the use of an in situ analytical technique based on simultaneous displacement and resistance measurement of gas diffusion layers (GDLs) used in polymer electrolyte fuel cells (PEFCs), when exposed to varying compaction pressure. In terms of the losses within fuel cells, the ohmic loss makes up a significant portion. Of this loss, the contact resistance between the GDL and the bipolar plate (BPP) is an important constituent. By analysing the change in thickness and ohmic resistance of GDLs under compression, important mechanical and electrical properties are obtained. Derived parameters such as the ‘displacement factor’ are used to characterise a representative range of commercial GDLs. Increasing compaction pressure leads to a non-linear decrease in resistance for all GDLs. For Toray paper, compaction becomes more irreversible with pressure with no elastic region observed. Different GDLs have different intrinsic resistance; however, all GDLs of the same class share a common compaction profile (change in resistance with pressure). Cyclic compression of Toray GDL leads to progressive improvement in resistance and reduction in thickness that stabilises after ∼10 cycles. Show less