A locally resolved investigation on direct methanol fuel cell uneven components fading: Local cathode catalyst layer tuning for homogeneous operation and reduced degradation rate

Kurzfassung

Durability issues of direct methanol fuel cell still hinder technology widespread commercialization; uneven aging of MEA components, generally harsher in air outlet region, is known to exasperate overall performance degradation. In a previous work, the authors selected a stable cathode electrode, demonstrated to fade homogenously: uneven water-related limitations, such as dehydration and flooding, were revealed to locally worsen performance at cathode inlet and outlet regions, leading to current redistribution. Aiming to reduce degradation rate, in this work homogeneous current distribution during operation is pursued by tuning MEA properties to meet local operating conditions. A properly improved 1D+1D physical model is used to support the development of a gradient MEA, featuring 1.6 mg cm−2 and 0.8 mg cm−2 of catalyst and ionomer respectively at inlet/ outlet and center regions of cathode electrode. Tests based on custom macro-segmented cell demonstrated 55% more homogeneous current distribution, controllable during operation by means of cathode air stoichiometry. 500 h degradation test revealed 70% decreased degradation rate from uniform MEA (11 μV h−1) with a homogenous fading of performance. An 18% lower Pt nanoparticle growth at cathode outlet and limited ionomer degradation at cathode inlet were identifed by ex-situ analyses (TEM and XPS), indicating locally mitigated fading mechanisms.