Durable Oxygen Evolution Catalysts for Alkaline Membrane Water Electrolysis

Abstract

The utilization of renewable energy has substantially driven more attention into electrolysis technologies. An electrolyzer can utilize “off peak” electricity from solar or wind farms to produce hydrogen or other fuels. These chemicals can then be operated in a fuel cell mode to generate electricity when needed or used for other industrial applications. However, current hydrogen production from electrolysis comprises only a small fraction of the global hydrogen market due to the high costs that results from expensive materials even if “free” electricity from renewable energy can be acquired. Alkaline membrane water electrolysis enables to use non-precious metals (or oxides) as the catalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). This is very meaningful as the commercial OER catalyst IrOx for proton exchange membrane (PEM) electrolysis is very expensive; more importantly, the global storage and production of iridium is very scarce, tremendously limiting the mass production and deployment of PEM electrolyzers. However, there have rarely reported active and durable OER and HER catalysts for alkaline membrane water electrolysis, particularly in a membrane and electrode assembly (MEA) level; most previous studies on the OER and HER catalysts were focused on the rotating disk electrodes (RDEs). We have investigated a series of OER catalysts including Co3O4 supported on carbon nanotubes (Co3O4/CNTs), binary transitional metal oxides (nickel cobalt oxide, NiCo2O4), and nanocarbon composites (FeCoNiMn-derived N-doped graphene tube, NC-FeCoNiMn4). These catalysts have first demonstrated remarkable durability in the RDE tests, subject to extensive voltage cycling from 0.0 V to 1.9 V. These catalysts have been integrated with other components including alkaline membrane and ionomer to test their MEA performance. It was discovered that both membrane and ionomers have a significant impact on the MEA performance and durability. The alkaline membrane and ionomer can quickly degrade upon high-voltage operations, leading to rapid MEA performance decay. However, the decayed performance can be restored after the introduction of diluted hydroxide solution (e.g, 0.1 M KOH) to the electrolyzer cell. Therefore, this work can provide insightful guidance on the MEA design for alkaline membrane water electrolysis. Most importantly, the interaction between the catalyst and the ionomer will be investigated. Acknowledgement: The project is financially supported by the Department of Energy’s Fuel Cell Technology Office under the Grant DE-EE0006960.