Metal Oxide Nanocrystals Supported on Carbon Nanotubes As Bifunctional Electrocatalysts in Reversible Alkaline Membrane Fuel Cells

Abstract

Hybrid structure of Co3O4 nanocrystals supported on carbon nanotubes (CNTs) was previously synthesized in our lab, and it exhibits excellent bifunctional oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) activities in alkaline media. More importantly, the hybrid nanomaterials showed great durability in a broad cycling potential range, from 0.0 V to 1.9 V (vs. RHE), which is a harsh environment that no previous hybrid structure reported has demonstrated stability in. In this study, we further explored other types of structure using similar synthesizing procedure, but different metal precursors (forming single, binary or ternary oxide solid solution with cobalt acetate, nickel acetate, manganese acetate, iron acetate or copper acetate) and solvents to pursue better performance. Other parameters such as CNT size and post-treatment conditions were also altered to optimize the synthesis procedure. The CNT-based hybrid electro-catalysts were made into membrane electrode assemblies (MEAs) to be tested in reversible alkaline fuel cells. The MEA fabrication was optimized in aspects of: catalyst ink preparation (by tuning the ionomer type, ionomer/catalyst ratio, and sonication length), membrane selection (alkaline membrane types, pre- and post- activation), catalyst-coated membrane fabrication (painting, spraying, hot pressing condition) and cell assembly. The MEAs were then tested in fuel cell mode and electrolyzer mode intermittently. MEA structural characterizations were carried out before and after these tests to study catalyst degradation mechanisms. This work may provide perspectives for bifunctional catalyst synthesis and MEA design for reversible alkaline fuel cells. Acknowledgement:The project is financially supported by the Department of Energy’s Fuel Cell Technology Office under the Grant DE-EE0006960.