Skillful Introduction of Urea during the Synthesis of MOF-Derived FeCoNi-CH/p-rGO with a Spindle-Shaped Substrate for Hybrid Supercapacitors.

A composite (FeCoNi-CH/p-rGO) with a spindle-shaped substrate is controllably prepared by combining FeCoNi carbonate hydroxide (FeCoNi-CH) and partially reduced graphite oxide (p-rGO) using a novel chemical strategy. In the synthetic process, urea is introduced as the precipitant and reducing agent. MIL-88A as a self-template is converted into a ternary-metal CH composite, maintaining the original morphology by the metal ion etching and coprecipitation method, and graphite oxide is reduced to rGO with stronger conductivity partially at the same time. The electrochemical performance of the FeCoNi-CH/p-rGO is superior to FeCoNi-CH, with a high specific capacitance (1346 F g -1 at 0.5 A g -1 ) and rate capability (55.5% at 10 A g -1 ). The better electrochemical performance of the FeCoNi-CH/p-rGO composite is attributed to the pseudocapacitive energy storage capacity caused by the synergistic action of ternary-metal CH and the high conductivity of p-rGO. Meanwhile, the uniform mixture of FeOOH/activated carbon (AC) is fabricated as an anode to instead of the pure FeOOH or AC, which leads to the balancing energy density and high cycle stability of the hybrid supercapacitor (HSC). The corresponding assembled FeCoNi-CH/p-rGO//FeOOH/AC HSC exhibits a high energy density of 46.93 W h kg -1 at 400 W kg -1 power density and a cycle stability of 66.7% after 3000 cycles. In addition, this work also provides a facile method to fabricate metal-organic framework-derived ternary-metal CH/p-rGO composite materials, which could be applied in the fields of supercapacitors and other fields.