(510b) Bifunctional Catalyst Enabled Reversible Fuel Cells for Energy Storage (Invited)

Reversible fuel cells have been considered as a device for energy storage due to their low cost and high-energy storage capacity. The oxygen electrode reactions are one of the primary limiting factors of reversible fuel cells, due to high overpotential caused by sluggish oxygen reduction and evolution kinetics. Bifunctional non-platinum group metal (PGM) electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) have been developed to lower the overpotential on the oxygen electrode, using hybrid structure of metal oxide supported on advance carbon nanotubes [1], transition metal derived graphene tubes [2] or structurally modified transition metal oxides. Hybrid structure of Co₃O₄ nanocrystals supported on carbon nanotubes (CNTs) has been synthesized in our lab, which exhibits excellent bifunctional ORR/OER activities in alkaline media. More importantly, the hybrid nanomaterials showed tremendous durability under a harsh potential cycling condition, from 0.0 V to 1.9 V (vs. RHE), using a rotating disk electrode (RDE).

In addition to RDE tests, the bifunctional catalysts have been integrated with anion exchange membranes and ionomers to construct membrane and electrode assemblies (MEAs). The MEAs have been optimized in aspects of: catalyst ink preparation (tuning the ionomer type, ionomer/catalyst ratio), alkaline membrane selection, and electrode fabrication (painting, spraying, hot pressing condition). The MEAs have been operated in fuel cell mode and electrolyzer mode intermittently to test their reversibility. The MEA microstructures have been characterized before and after these tests to study bifunctional catalyst degradation mechanisms. The enabled reversible fuel cells can be used for large-scale renewable energy storage due to their high energy density and low cost.

References

[1] Zhao, Shuai, et al. "Highly durable and active Co3O4 nanocrystals supported on carbon nanotubes as bifunctional electrocatalysts in alkaline media." Applied Catalysis B: Environmental 203 (2017): 138-145.

[2] Gupta, Shiva, et al. "Highly Active and Stable Graphene Tubes Decorated with FeCoNi Alloy Nanoparticles via a Template‐Free Graphitization for Bifunctional Oxygen Reduction and Evolution." Advanced Energy Materials 6.22 (2016).

Acknowledgement: The project is financially supported by the Department of Energy’s Fuel Cell Technology Office under the Grant DE-EE0006960.