Electrochemical activation of venus flytrap-like CoP and Co3O4 for boosting the supercapacitance performance

Electrochemical activation tactic can be adopted to boost electrochemical performance of electrodes by adjusting the composition and microstructure. Herein, venus flytrap-like CoP nanostructures and corresponding Co3O4 precursor are synthesized on nickel foam (NF) framework, and the electrochemical activation mechanisms of CoP and Co3O4 are investigated in KOH electrolyte. When endured for 100 CV cycles, the activated CoP exhibits a 3D framework structure consisted of thin nanosheets, and the discharge capacity enhances to 1536 C g−1 at 1 A g−1 from initial capacity of 663 C g−1. The enhanced performance is due to the composition transition from upper CoP and beneath NiP to NiCo-hydroxides and NiCoOOH, and the microstructure transition from nanoneedles to 3D framework structure stacked by thin nanosheets. Different from the transition mechanism of NF/CoP, seldom microstructure transitions are occurred for the Co3O4 precursor, only involving the change of nanoneedle diameter. The activation of Co3O4 induces a limited capacity enhancement from 242 to 623 C g−1, due to a simple transition from oxides to oxyhydroxides. The application performance of NF/CoP is investigated by assembling asymmetric supercapacitor with NF/AC. The device releases a discharge capacitance of 137 F g−1 at 1 A g−1, and the capacitance retention is 77.4% when cycling for 5000 cycles. The energy density is 48.7 W h kg−1 at 804.4 W kg−1. Compared with existing Co-based phosphides, activated NF/CoP electrode exhibits an obvious performance advantage in supercapacitors.