Hierarchical ZnCo2 O4 @NiCo2 O4 Core-Sheath Nanowires: Bifunctionality towards High-Performance Supercapacitors and the Oxygen-Reduction Reaction.

Increasing energy demands and worsening environmental issues have stimulated intense research on alternative energy storage and conversion systems including supercapacitors and fuel cells. Here, a rationally designed hierarchical structure of ZnCo2 O4 @NiCo2 O4 core-sheath nanowires synthesized through facile electrospinning combined with a simple co-precipitation method is proposed. The obtained core-sheath nanostructures consisting of mesoporous ZnCo2 O4 nanowires as the core and uniformly distributed ultrathin NiCo2 O4 nanosheets as the sheath, exhibit excellent electrochemical activity as bifunctional materials for supercapacitor electrodes and oxygen reduction reaction (ORR) catalysts. Compared with the single component of either ZnCo2 O4 nanowires or NiCo2 O4 nanosheets, the hierarchical ZnCo2 O4 @NiCo2 O4 core-sheath nanowires demonstrate higher specific capacitance of 1476 F g(-1) (1 A g(-1) ) and better rate capability of 942 F g(-1) (20 A g(-1) ), while maintaining 98.9 % capacity after 2000 cycles at 10 A g(-1) . Meanwhile, the ZnCo2 O4 @NiCo2 O4 core-sheath nanowires reveal comparable catalytic activity but superior stability and methanol tolerance over Pt/C as ORR catalyst. The impressive performance may originate from the unique hierarchical core-sheath structures that greatly facilitate enhanced reactivity, and faster ion and electron transfer.