Revealing localized compression induced degradation mechanisms in polymer electrolyte membrane water electrolyzers

We present the first multi-physics model for the polymer electrolyte membrane water electrolyzer (PEMWE), coupling mechanical compression with electrochemical reactions to predict the effect of mechanical compression on cell performance. Under compression, the catalyst layer (CL) and membrane deform more significantly than the porous transport layer (PTL). Quite alarmingly, the membrane experiences thinning, most significantly under the lands, making the land regions of the membrane particularly susceptible to fuel crossover. Compression also results in higher mass transport resistance and lower liquid water saturation in the CL due to reduced single and two-phase permeabilities of the CL (liquid water saturation decreases by 43.6 % when increasing the compression ratio (CR) from 5 % to 30 %). Despite the drawbacks of compression, for CR < 20 % cell performance is greatly improved, and we attribute this improvement to the substantial decrease in the PTL/CL interfacial contact resistance (which outweighs the trade-off with mass transport resistances). However, there are negligible benefits to increasing the CR above this 20 % threshold, beyond which local mass transport resistances in the CL dominate electrochemical performance (mass transport resistances increase 59 % at a CR of 30 %; whereas ohmic resistances decrease by only 8 %). While the bulk electrochemical performance does not change significantly with CR > 20 %, the local current density under the land decreases, which we attribute to increases in local mass transport resistances in the CL.