Electrically Insulated Catalyst–Ionomer Anode Interfaces toward Durable Alkaline Membrane Electrolyzers

Abstract

Anion-exchange-membrane water electrolysis (AEMWE) is an emerging technology for scalable hydrogen production. AEMWE has poor durability when operating without supporting electrolyte due to the oxidation of ionomers and membranes in contact with the anode oxygen evolution reaction (OER) catalyst. We report a new "passivated" anode architecture for AEMWE where the OER catalysts and ionomers are physically separated with a thin film amorphous oxide coating that is electrically insulating but conductive to hydroxide ions. We find that 2−3 nm of HfO x passivation layers show sufficient hydroxide ion transport to minimally limit the cell performance while suppressing ionomer degradation with both Ir (500 mA•cm −2 for 40 h) and CoO x (1.0 A•cm −2 for 100 h) model porous-transport-layer-supported catalysts in AEMWE. This interfacial engineering approach guides electrode design to improve the durability of AEMWE, particularly for systems operating with pure-water feed.

Addressing the Challenge of Electrochemical Ionomer Oxidation in Future Anion Exchange Membrane Water Electrolyzers

“…Innovative ideas and their implementations to mitigate ionomer electrochemical oxidation is on going. For example, a recent paper reports the introduction of a passivated layer (2–3 nm thick of HfO x ) that allows hydroxide ion transport but shows undesirable ionomer adsorption …”

Divergent Synthesis of Bipolar Membranes Combining Strong Interfacial Adhesion and High-Rate Capability

“…This may be related to degradation of the electrodes at high current densities. Although ex situ studies have shown that the SEBS_AEL shows relatively good stability in 1 M KOH at 60 °C during 30 days, substitution of the cationic head groups with more stable chemistries in combination with the introduction of alkyl spacers to circumvent common degradation pathways will in any case be expected to improve the operating lifetime, perhaps in combination with a protective barrier layer between catalysts and ionomer to mitigate anode degradation …”