Biochar induced low body phase g-C3N4 with high crystallinity in situ grown NiSe2 nanoparticles for hybrid supercapacitor

Abstract

Nickel selenide, as hybrid supercapacitor electrode material, has excellent electrochemical performance. However, it also faces challenges, such as slow charge transfer speed, easy agglomeration, and volume expansion. Here, we prepared a high crystalline graphitic carbon nitride (CCN)/biochar (C)/nickel selenide (NiSe₂) (CCN/C-NiSe₂) ternary composite material as the positive electrode to solve the problems mentioned above. After introduction of C, the few layers and low body phase of g-C₃N₄ (CN) can be obtained by utilizing its self-assembly and micro-reaction space characteristics. Furthermore, CN with many defects and low crystallinity degree can be improved by introducing molten salt system, so as to obtain CCN. The strong interconnections between the π-conjugated layer of CCN and the biochar promote electron and ion transport efficiency, which can increase the charge transfer speed, decrease accumulation agglomeration and poor stability of NiSe₂. The results show that the specific capacitance of CCN/C-NiSe₂-90 nanocomposite electrode is 1309.75 F g⁻¹ (1 A g⁻¹), which is significantly higher than that of NiSe₂ (965.75 F g⁻¹) and CCN/C (74 F g⁻¹) in the three-electrode system. The CCN/C-NiSe₂-90//AC presents energy density of 28.66 Wh kg⁻¹ at 849.88W kg⁻¹, and its initial performance maintains 80 % capacitance after 5000 cycles (5 A g⁻¹).