Bifunctional oxygen evolution and supercapacitor electrode with integrated architecture of NiFe-layered double hydroxides and hierarchical carbon framework

Layered double hydroxide with exchangeable interlayer anions are considered promising electro-active materials for renewable energy technologies. However, the limited exposure of active sites and poor electrical conductivity of hydroxide powder restrict its application. Herein, bifunctional integrated electrode with a 3D hierarchical carbon framework decorated by nickel iron-layered double hydroxides (NiFe-LDH) is developed. A conductive carbon nanowire array is introduced not only to provide enough anchoring sites for the hydroxide, but also affords a continuous pathway for electron transport throughout the entire electrode. The 3D integrated architecture of NiFe-hydroxide and hierarchical carbon framework possesses several beneficial effects including large electrochemical active surfaces, fast electron/mass transport, and enhanced mechanical stability. The as-prepared electrode affords a current density of 10 mA cm^-2 at a low overpotential of 269 mV for oxygen evolution reaction (OER) in 1 M of KOH. It also offers excellent stability with negligible current decline even after 2000 cycles. Besides, density functional theory calculations revealed that the (110) surface of NiFe-LDH is more active than the (003) surface for OER. Furthermore, the electrode possesses promising application prospects in alkaline battery-supercapacitor hybrid devices with a capacity of 178.8 mAh g^-1 (capacitance of 1609.6 F g^-1) at a current density of 0.2 A g^-1. The viability of the as-prepared bifunctional electrode will provide a potential solution for wearable electronics in the near future.