3D self-branched zinc-cobalt Oxide@N-doped carbon hollow nanowall arrays for high-performance asymmetric supercapacitors and oxygen electrocatalysis

This study reports the design and fabrication of ultrathin zinc-cobalt oxide nanoflakes@N-doped carbon hollow nanowall arrays (ZnCo2O4@NC NWAs) from vertically aligned 2D Co-MOF solid nanowall arrays by controllable cation ion-exchange and post annealing strategies. The unique 3D self-branched nanostructure anchored on flexible carbon textiles (CTs) can offer short ion diffusion length, fast and continuous electron transport pathway, and abundant reaction active sites. More importantly, the rational incorporation of Zn2+ generates hollow structure as well as reduces the intrinsic band gap, which further enhance the ion transportation efficiency and electronic conductivity. The above superiorities endow the 3D self-branched ZnCo2O4@NC/CTs electrodes with remarkable performances in terms of flexible asymmetric supercapacitor and oxygen electrocatalysis. When evaluated as a flexible cathode for asymmetric supercapacitor, the as-fabricated ZnCo2O4@NC/CTs electrode exhibits outstanding electrochemical performance with a wide work voltage up to 2.0 V, high areal energy density of 0.278 mWh cm(-2) (or volumetric energy density of 2.32 mWh cm(-3)) and long-term cycling stability (similar to 85.89% capacitance retention over 6000 cycles). Additionally, the ZnCo2O4@NC/CTs electrode shows excellent oxygen evolution reaction (OER) performance with a small overpotential of 196.4 mV at 10 mA cm(-2) and long-term durability (over 45 h). This work provides a rational design strategy for controllable synthesis of 3D self-branched hollow nanostructure on flexible substrate for energy storage and conversion applications.