Hierarchical mesoporous NiO nanosheet arrays as integrated electrode for hybrid sodium-air batteries.

Attributed to its environmental friendliness, high theoretical energy density, and abundant sodium resource, rechargeable hybrid sodium-air batteries (HSABs) are expected to become a promising pioneer of the new-generation green energy storage device. However, HSABs suffer from the high voltage gap, low energy conversion efficiency, and poor cycle stability due to the low catalytic activity of catalysts caused by the degradation of polymer binders. Herein, hierarchical mesoporous NiO nanosheet arrays grown on carbon papers (CP) (NiO NA@CP) were synthesized by a facile and efficient hydrothermal route and calcination process, which acts as an integrated electrode for HSABs. Compared with traditional air electrodes that contain a polymer binder and conductive carbon, the integrated NiO NA@CP electrode prevents the aggregation of catalysts, improves the electronic conductivity by good electric contact and ensures its robust mechanical stability. In addition, NiO NA@CP electrode with the abundant porosity and large specific area offers plenty of active sites and shortens ion transfer length and rapid mass transport in ORR/OER process, leading to excellent oxygen catalytic activities. HSABs with NiO NA@CP electrode show a low overpotential of 0.65 V, a state-of-the-art power density (7.53 mW cm−2), as well as an excellent cyclability of 170 cycles (over 170 h) at a current density of 0.1 mA cm−2. [ABSTRACT FROM AUTHOR]