Ultrathin CoNi-P, S nanosheets electrodes enabled by N-doped graphene quantum dots with enhanced electron transfer capability for asymmetric supercapacitors

Developing high-performance cobalt–nickel (CoNi) based electrode materials with high specific capacitance, excellent rate performance, and outstanding cycling stability is crucial for advanced asymmetric supercapacitors (ASCs). In this paper, a novel nitrogen-doped graphene quantum dots (N-GQDs) @CoNi-P, S (N/CoNi-P, S) composite electrode is constructed via a facile two-step electrochemical deposition method. The introduction of N-GQDs significantly enhances the electronic structure and surface activity of CoNi-P, S, while sulfur doping can increase crystal defects, expanding the electron transport pathways of the N/CoNi-P, S electrode. Density functional theory (DFT) calculations reveal that N-GQDs can induce electron transfer to CoNi-P, S, resulting in the formation of a built-in electric field at the interface, which enhances the electron transfer capability of N/CoNi-P, S. And the energy storage enhancement mechanism is proposed, in which N-GQDs facilitate rapid interfacial electron transfer via hole conduction, thereby accelerating the electrochemical reaction kinetics of N/CoNi-P, S. The N/CoNi-P, S electrode exhibits a remarkable specific capacitance of 3100.4 F g⁻¹ at 1 A g⁻¹, excellent rate capability with 85.8 % capacitance retention at 30 A g⁻¹ and outstanding cycle stability (106.7 %, 8000 cycles). The assembled N/CoNi-P, S//active carbon (AC)-ASC delivers a high energy density of 60.35 Wh kg⁻¹ at 1125 W kg⁻¹ and outstanding cycling stability with 93.7 % capacitance retention after 10,000 cycles. This study provides new insights into designing high-performance CoNi based electrode materials for energy storage.