Boosting Energy Efficiency of Nickel Cobaltite via Interfacial Engineering in Hierarchical Supercapacitor Electrode

Hybrid electrodes with electroactive components on conductive substrates have been demonstrated to be an effective strategy to achieve high energy and power density in supercapacitors. However, the mismatch of interface property could be a huge hurdle to further improve energy storage performance and long-term stability. In this work, an interfacial metal seeding approach has been developed targeting strengthening of the interfacial interaction between electroactive NiCo₂O₄ nanostructure and carbon substrate as well as to promote electron transfer across the interface. By implanting low-concentration nickel (Ni) nanoparticles at the interface, the electrochemical capacitance of NiCo₂O₄ was boosted up to 2367 F/g at a current density of 1 A/g in a symmetric two-electrode configuration, which is about 2 times higher than the capacitance obtained from the electrode without metal seeds. The Ni seeds also contribute to an excellent cycling retention of >96% after 5000 cycles, where only 65% capacitance was retained in the electrode without Ni seeds. A synergistic contribution of promoted interfacial interaction, reduced internal resistance, enlarged surface area, and mesoporous NiCo₂O₄ nanorod structure leads to a boosted energy efficiency of NiCo₂O₄ in this study. A comparative study on different metal nanoparticles (nickel, cobalt, and iron) reveals that not only metal species but also particle concentration play significant roles in determining the energy storage property of the hierarchical NiCo₂O₄/carbon electrodes.