Biomimetic Construction of Ferrite Quantum Dot/Graphene Heterostructure for Enhancing Ion/Charge Transfer in Supercapacitors

Abstract Spinel ferrites are regarded as promising electrode materials for supercapacitors (SCs) in virtue of their low cost and high theoretical specific capacitances. However, bulk ferrites suffer from limited electrical conductivity, sluggish ion transport, and inadequate active sites. Therefore, rational structural design and composition regulation of the ferrites are approaches to overcome these limitations. Herein, a general biomimetic mineralization synthetic strategy is proposed to synthesize ferrite (XFe₂O₄, X = Ni, Co, Mn) quantum dot/graphene (QD/G) heterostructures. Anchoring ferrite QD on the graphene sheets not only strengthens the structural stability, but also forms the electrical conductivity network needed to boost the ion diffusion and charge transfer. The optimized NiFe₂O₄ QD/G heterostructure exhibits specific capacitances of 697.5 F g⁻¹ at 1 A g⁻¹, and exceptional cycling performance. Furthermore, the fabricated symmetrical SCs deliver energy densities of 24.4 and 17.4 Wh kg⁻¹ at power densities of 499.3 and 4304.2 W kg⁻¹, respectively. Density functional theory calculations indicate the combination of NiFe₂O₄ QD and graphene facilitates the adsorption of potassium atoms, ensuring rapid ion/charge transfer. This work enriches the application of the biomimetic mineralization synthesis and provides effective strategies for boosting ion/charge transfer, which may offer a new way to develop advanced electrodes for SCs.