Abstract
The mechanical compression used in the construction of PEFCs improves effective current collection and gas sealing, however it results in structural deformation of the MEA, affecting reactant transport with adverse consequences for the electrochemical performance of the cell. The present study uses X-ray CT to characterise MEA under compression and determine effective properties of the porous domain. The comprehensive modelling approach couples a structural model of the MEA under compression to a multi-phase, non-isothermal electrochemical performance model. Liquid water saturation in the cathode domain that promotes mass transport losses is validated with neutron radiography. Here, the structural model considers the fuel cell stacking process at three compressions and highlights the non-uniform distribution of porosity and effective properties under non-uniform cell compression, affecting localised current distribution and water transport. An increase in compression showed a negligible effect on the performance in the activation region, the performance was marginally improved in the ohmic region and significantly affected in mass transport region, promoting cell flooding. The non-uniform compression effects are found to be important considerations for robust modelling studies as it increases the nonuniformity in localised current, temperature and flooding that would further alter the durability of the fuel cell.
Highlights
High power density, low operating temperature and high efficiency make polymer electrolyte fuel cells (PEFCs) an attractive alternative to conventional power sources [1,2]
A membrane electrode assembly (MEA) typically consists of a poly mer electrolyte membrane, microporous layer (MPL), gas diffusion layer (GDL) and catalyst layer (CL) which are arranged between bipolar plates, in which flow-field channels are machined for transportation of gas and product water
The vertical deformation of the GDL agrees with the well-known ‘tenting’ behaviour of the GDL under the channel region that results in partial blocking of the active channels [15]
Summary
Low operating temperature and high efficiency make polymer electrolyte fuel cells (PEFCs) an attractive alternative to conventional power sources [1,2]. While increasing the cell compression im proves the electrical and thermal conductivities of GDLs, it results in a loss of pore volume, primarily in the region under the land This results in a loss of GDL porosity and permeability, and an increase in mass transport resistance [10,11]. The effect of compression on fuel cell performance was studied experimentally by Mason et al using electrochemical impedance spectroscopy (EIS) [16] They reported an improvement in contact resistance between the GDL and bipolar plate with an increase in compression. A trade-off between electrical contact resistance and mass transport limitation due to flooding was confirmed in this study While such experimental investigations provide great insight into fuel cell operation, the slow iterative nature of systematically varying design and operational conditions makes modelling a powerful design tool to examine the effect of compression
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