Nanosheet-structured NiCoO₂/carbon nanotubes hybrid composite as a novel bifunctional oxygen electrocatalyst

Synthesis of novel bifunctional catalysts based on earth-abundant elements with high catalytic activities for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) becomes a main strategy to promote the development of metal-air batteries and fuel cells. Herein, a novel Co²⁺-based mixed transition metal oxide composite, the three-dimensional (3D) nanosheet-structured NiCoO₂/carbon nanotubes (CNTs) composite, was successfully synthesized through a facile one-pot method. The better electrocatalytic activities of NiCoO₂/CNTs for both ORR and OER than those of pure NiCoO₂, CNTs, physically mixed NiCoO₂ and CNTs, and Co₃O₄/CNTs are proved. The comparison of local ORR and OER electrocatalytic activities of NiCoO₂/CNTs to other catalysts are obtained by scanning electrochemical microscopy (SECM) characterizations. The closed oxygen reduction peak and half-wave potentials, nearly four-electron dominated process, better methanol tolerance and electrochemical stability confirm the comparable electrocatalytic performance and better stability of NiCoO₂/CNTs to the commercial Pt/C catalyst for ORR. The similar stability of NiCoO₂/CNTs demonstrates its comparable electrocatalytic performance to the state-of-the-art RuO₂ catalyst for OER. The as-prepared NiCoO₂/CNTs composite presents as a promising bifunctional oxygen electrocatalyst in alkaline solution for potential applications.