(345e) Materials, Integration, and Durability Challenges in Low Temperature Electrolysis

Hydrogen has unique advantages as an energy carrier, with a high energy density and abilities for long-term storage and conversion between electricity and chemical bonds.[1] Although hydrogen currently has a significant role in transportation and agriculture, its use in energy consumption overall has been limited, particularly in the case of electrochemical water splitting. With decreasing electricity prices, electrolysis cost reductions can be achieved and allow for an opportunity for greater use.

In proton exchange membrane (PEM) -based electrolyzers, long-term durability issues arise when targeting low-cost hydrogen production, both through intermittent power inputs and anticipated PGM loading reductions. Accelerated stress tests have been developed that focus on anode catalyst layer durability and membrane/transport layer interfaces, due to intermittent and start-stop operation.[2] In general, performance changes manifest through kinetics and correspond to catalyst migration, interfacial tearing, and layer changes, including catalyst agglomeration and ionomer segregation.[3] Mitigation strategies, both operational and materials, have been developed to lessen these losses.

In anion exchange membrane (AEM) systems, the alkaline environment allows for non-PGM components and improved durability at high pH. Operation in AEM electrolysis includes supporting (hydroxide, carbonate) and unsupported (water) electrolytes, and outlook depends on the intended market.[4] Recent component advancements have enabled high performance, particularly in supporting electrolytes. PGM-free catalysts are readily available that are competitive with and can exceed the activity and stability of their PEM-PGM counterparts. Differences in catalyst particle sizes and ink stability, and transport layer properties, however, create challenges in optimizing catalyst layer properties and interfacial contact, and minimizing catalyst layer resistances.[5,6] Select ionomer and catalyst combinations have been evaluated for differences in ionomer-catalyst affinity and their impact on activity and stability in the oxygen evolution reaction. These experiments demonstrate the complications of developing a single set of materials and test protocols for component evaluations.