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Cerium oxide-containing interlocking interfacial layer improved mechanical adhesion and chemical stability of the interface. For the first time as a hydrocarbon-based membrane, it operated stably for more than 500 hours.

The durability of the membrane electrode assembly (MEA) is one of the important requirements for the successful commercialization of anion exchange membrane fuel cells (AEMFCs). While chemical stabilities of the components (the catalyst, membrane, and ionomer) have been assessed by ex situ tests, the degradation mode of the components in a single-cell is still not fully understood. Herein, the degradation of a MEA based on an ionomer having a polycarbazole main chain and a trimethyl ammonium side group was systematically investigated for a single-cell level under constant current conditions. The degradations of the catalyst, membrane, and ionomer were compared by in situ electrochemical and ex situ post-mortem analyses. The catalyst and ionomer in the cathode showed significant degradation, whereas the membrane was relatively durable, suggesting that the formation of a strong alkaline environment in the cathode catalyst layer is a major cause of the performance fade. The use of an alkaline-stable ionomer with an N,N-dimethylhexylamine group, which is designed based on density functional theory (DFT) calculations, in the cathode catalyst layer leads to 87% durability improvement. This work enhances the understanding of the key factors affecting the durability of AEMFCs under real operation and suggests practical strategies toward higher durability.

Ionomer films even only a few nanometers thick in the catalyst layer of a polymer electrolyte membrane fuel cell are detrimental to the power performance at low Pt loadings due to their large oxygen transport resistance. Therefore, removing the ionomer films on the Pt surface for oxygen transport while preserving them on the carbon surface for proton transport can be an ideal ionomer distribution. Herein, we achieve ionomer-lean Pt surfaces by masking the Pt nanoparticles of the Pt/C catalyst with an alkanethiol. Due to the weakening of the ionomer/Pt interaction by the molecular mask, a low population of ionomers on the Pt surface is achieved while preserving the fast proton transport in the catalyst layer. The alkanethiol is then electrochemically removed from the catalyst layer, recovering the catalytic activity of the Pt. Electrochemical analyses showed a reduced oxygen transport resistance through the ionomer film and a consequent enhancement of the power performance. This molecular masking strategy marks the beginning of the nano-scale control of ionomer distribution in the development of advanced fuel cells.