Model-Driven Membrane Electrode Assembly Design for High-Performing Open-Cathode Polymer Electrolyte Membrane Fuel Cells

Abstract

Open-cathode fuel cells use air cooling to effectively reduce system cost. However, due to the challenging hygrothermal environment, they generally suffer from low performance compared to conventional, liquid-cooled cells. A pre-validated, three-dimensional computational model is used in the present work to determine the effects of different sub-component designs, namely the polymeric membrane, composition of the cathode catalyst layer (CCL), and structure of the cathode microporous layer (CMPL), on the performance of an open-cathode fuel cell. This comprehensive parametric study performed on a total of 90 cases shows the increment in current density to be 7% and 31% by improvising the membrane and CCL design, respectively, at 0.6 V. A steep increase of 87% is also achieved by strategically modifying the CMPL design at 0.4 V operation. An overall increment of 119% and 131% in current density is achieved for the best membrane electrode assembly (MEA) design at 0.6 and 0.4 V, respectively, as compared to the baseline design. These improvements are achieved by collective improvements in kinetics, oxygen mass transport, ohmic resistance, self-heating, and water retention in the ionomer phase. The proposed MEA design could facilitate open-cathode fuel cell stacks with 2× higher power output or 56% lower weight and materials cost for a given power demand.

Experimental Design of High-Performing Open-Cathode Polymer Electrolyte Membrane Fuel Cells

“…This outcome is likely a result of enhanced O 2 availability at the active sites of the CCL in the presence of a more porous and thinner GDL. 15,41 These experimental results are comparable to our previously published modelling predictions 11,14 where a 3D computational fuel cell model was used to establish the effect of ionomer property changes, membrane changes, and MPL/GDL modifications for opencathode PEMFCs. The model revealed the theoretical benefits of an ionomer with low water sorption/desorption rate constant (γ) to aid water retention at the CCL and thereby increasing the CD performance by up to 130% at 0.6 V. 14 Similar water retention capability is featured experimentally in the present work by use of SSC ionomer with low EW over conventional LSC ionomers.…”

“…The reduced GDL thickness and increased porosity are expected to jointly reduce the O 2 diffusion resistance in the MEA with increased O 2 availability at the active sites of the cathode CL (CCL). 15,41 This leads to an enhanced rate of reaction and thus resulting in increased CD.…”

“…14 Based on predictions from computational modelling of an opencathode cell, lower γ ionomer is anticipated to support the cell performance by providing better water retention capability within the ionomer phase of the CL. 15 To date however, there are no experimental reports available to corroborate these predictions. The equivalent weight (EW) of the ionomer has also been reported to influence the cell performance for open-cathode systems.…”