Hierarchical Co 3 O 4 nanorods anchored on nitrogen doped reduced graphene oxide: a highly efficient bifunctional electrocatalyst for rechargeable Zn–air batteries

• Published in: Catalysis science & technology 2020-03, Vol.10 (5), p.1444-1457
• Main Authors: Sanchez, Jaime S., Maça, Rudi Ruben, Pendashteh, Afshin, Etacheri, Vinodkumar, de la Peña O'Shea, Víctor A., Castillo-Rodríguez, Miguel, Palma, Jesus, Marcilla, Rebeca
• Format: Article
• Language: English
• ISSN: 2044-4753; 2044-4761
• DOI: 10.1039/C9CY02183C

Zn–air batteries are amongst the most promising energy storage technologies due to high theoretical energy density for which their practical application is tied to development of low-cost, effective bifunctional catalysts. Herein, a highly efficient bifunctional electrocatalyst was synthesized by hybridizing hierarchical spinel Co 3 O 4 nano-rods with N-rGO. A rational design of the nano-hybrid was realized through optimizing catalytic activity of the pure Co 3 O 4 NRs followed by their grafting onto N-rGO nanosheets. The optimized hybrid (N-rGO/Co 3 O 4 NRs) showed an excellent bifunctional (ORR/OER) catalytic activity with Δ E = E j=10 − E 1/2 as small as 0.78 V, outperforming state-of-the-art noble-metal catalysts ( e.g. PtRuC). Rechargeable Zn–air batteries assembled with a N-rGO/Co 3 O 4 NRs hybrid delivered a specific capacity of 875 mA h g Zn −1 (corresponding to an exceptional energy density of 1115 W h kg Zn −1 ), a peak power density of 47 mW cm −2 and a stable cycling stability compared to Zn–air batteries based on PtRuC commercial catalyst. Outstanding electrochemical performance of the hybrid ORR/OER catalyst is credited to the hierarchical nature of Co 3 O 4 NRs, optimized Co 3+ /Co 2+ ratio, particle agglomeration prevention and superior electrical conductivity resulting from the hybridization with N-rGO. Rational design of atomic-scale interfaces in the spinel metal oxide-carbon hybrid structures demonstrated here provides new insights for the designing and fabrication of high-performance bifunctional non-precious electrocatalysts for rechargeable Zn–air batteries.