Metal-organic framework-derived walnut-like hierarchical Co-O-nanosheets as an advanced binder-free electrode material for flexible supercapacitor

Abstract

Cobalt-based nanostructured are favorite pseudocapacitive electrode materials for supercapacitors (SCs) due to the low cost and high theoretical capacitance. However, their unsatisfied electrochemical stability severely limits them for practical applications. In this work, metal-organic framework (MOF) derived cobalt oxide (Co-O) hierarchical walnut-like nanosheets supported on carbon fiber cloth (CFC) (denoted as Co-O-NSs@CFC) as a binder-free electrode material was synthesized via scalable and facile hydrothermal method. Results exhibited that the Co-O-NSs@CFC showed crystalline and porous features with high surface area and can be utilized as cathode material for high-performance supercapacitors. The Co-O-NSs@CFC demonstrated excellent charge storage performance with balanced capacitive/diffusion-type charge storage (54% capacitive at 1 mV/s) and achieved 842 F/g (421 C/g) at 1 A/g with outstanding cycling stability of 96.4% till 10,000 cycles. Furthermore, a flexible asymmetric SC was assembled using activated carbon as anode and Co-O-NSs@CFC as a cathode with PVA/KOH as electrolyte (denoted as f-Co-O-NSs@CFC||AC). The f-Co-O-NSs@CFC||AC delivers a high specific capacitance of 178 F/g at 1.5 A/g, excellent energy density of 55.7 Wh/kg at a power density of 1125.9 W/kg with outstanding capacitance retention of 94.5% after 5000 cycles with stable flexible performance. This work shows a remarkable electrochemical performance that could offer high-energy-density electrode materials for flexible SCs.