Highly durable and active Co3O4 nanocrystals supported on carbon nanotubes as bifunctional electrocatalysts in alkaline media

• A hybrid structure of Co­3O4 decorated on oxidized CNT is introduced and synthesis-property relationships are discussed.
• The hybrid nanomaterial shows excellent ORR and OER activities, compared with Pt/C and Ir, respectively.
• The hybrid structure exhibits great durability in voltage cycling test from 0.0 V to 1.9 V (vs. RHE) potential range, an extreme harsh condition.
• Post-treatment by ammonia reduction plays a key role for restoring the durability of the hybrid structure.

Unitized regenerative alkaline membrane fuel cells (AMFCs) have recently attracted great attention as both an energy conversion and energy storage technology due to their low cost and high-energy storage density for renewable resources. The oxygen electrode has long been one of the primary limiting factors of reversible AMFCs due to the sluggish kinetics of the oxygen reduction and evolution reactions (ORR and OER, respectively). It is challenging to develop durable and efficient bifunctional ORR/OER electrocatalysts; in particular, few researchers have focused on the durability of the material, which is the most relevant aspect for industrial application of these catalysts. In this work, we present an optimized procedure producing a highly stable bifunctional hybrid catalyst with excellent ORR/OER activities. This catalyst comprises covalently-bonded hybrid structures of cobalt oxide nanocrystals decorated on pre-oxidized carbon nanotubes. We performed the durability test in a broad potential range, from 0.0 V to 1.9 V (vs. RHE), which is a harsh condition under which to our knowledge no previous hybrid structure in literature has survived. We have also linked the catalyst durability to metal oxide anchoring sites and its synthesis parameters. This study provides novel perspectives for the design of carbon-based, hybrid materials and insight into the synthesis-property relationships for the next-generation electrocatalysts.

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