Unique core-shell Co2(OH)2CO3@MOF nanoarrays with remarkably improved cycling life for high performance pseudocapacitors

• Unique core-shell composite electrode materials are facilely prepared. • Ultrahigh capacitance is achieved and comparable to most related electrodes. • Facilitated reaction kinetics and remarkably enhanced cycle life are accomplished. • The ASC delivers a high energy density of 55.2 Wh kg −1 @ 0.8 kW kg −1 . • The design strategy is applicable to other hydroxycarbonates based electrodes. Binder-free composite electrode material consisted of cobalt hydroxycarbonates (Co 2 (OH) 2 CO 3 ) and bimetallic metal-organic-framework (NiCo-MOF) is facilely prepared for the first time through a hydrothermal-solvothermal combined method. The composite Co 2 (OH) 2 CO 3 @MOF presents a unique core-shell architecture, which endows remarkable superiority such as great surface area, short diffusion pathway and component synergy effects, leading to splendid supercapacitor performance. The optimal composite electrode exhibits ultrahigh specific capacitance (3232 F g −1 at 1 A g −1 ), good rate capability and outstanding cycle life (84.1% after 5000 cycles). In addition, an asymmetric supercapacitor (ASC) device Co 2 (OH) 2 CO 3 @MOF-2//AC (active carbon) delivers a high energy density (55.2 W h kg −1 @ 0.8 kW kg −1 ) and excellent cycle life (89.2% after 6000 cycles). These values are comparable to or even better than the recently reported related electrode materials in literatures ( Table S1 ), demonstrating the prospect for future high performance energy storage devices. The smart strategy reported here can also be promoted to other metal hydroxycarbonates with advanced hierarchical core-shell structures for high performance electrochemical devices.