Fabrication of NH 4 F-tuned (Ni, Co) 2 (CO 3 )(OH) 2 for supercapacitor electrode

Transition metal compounds attract significant interest due to the promising application in energy storage devices. In this work, (Ni, Co) 2 (CO 3 )(OH) 2 is prepared via a hydrothermal route. In this method, NH 4 F is utilized to tune the growth rate of hydroxycarbonates. The morphological and crystalline nature evolution process of hydroxycarbonates is investigated by examining different addition amount of NH 4 F. Results show that the growth rate and the morphology and crystalline nature of hydroxycarbonates could be tuned through adjusting addition amount of NH 4 F. When there is no or a trace of NH 4 F in the system, sea urchin-like (Ni, Co) 2 (CO 3 )(OH) 2 with polycrystalline nature is synthesized, which shows high specific capacitance (1247 F g − 1 at 1 A g − 1 ) and stable cycling (remaining 96.3% of the initial capacitance after 3000 cycles). The addition of NH 4 F lowers the synthesis rate of hydroxycarbonates. With the help of large quantities of NH 4 F, hierarchical (Ni, Co) 2 (CO 3 )(OH) 2 with single-crystalline nature is fabricated, which shows moderate specific capacitance and long durability with 96.6% capacitance after 10,000 cycles, showing the promising application in supercapacitor. It is demonstrated that tuning of the morphology and crystalline nature of hydroxycarbonates is important in supercapacitor application.