Tunable fabrication of core-shell Ni-MnO₂ hybrid foams through structure-guided combustion waves for binder-free high-performance supercapacitor electrodes

Hybrid foam structures of metal and carbon are extensively used for electrochemical applications. However, their fabrication involves solution- or vacuum-processing, which damages the metal backbones or increases the fabrication time and cost. Herein, we report a tunable method for the scalable fabrication of core-shell metal-carbon hybrid foams using structure-guided combustion waves (SGCWs) and their application for the synthesis of core-shell Ni-MnO₂ hybrid foams as binder-free supercapacitor electrodes. SGCWs passing through the hybrids of nickel foams and chemical fuels, prepared by a wet impregnation method, enabled the direct fabrication of carbon coatings on the surfaces of the inner nickel backbones and yielded core-shell Ni@C. The incompletely combusted carbonaceous fuels in a few seconds, which were formed in the narrowly confined foam structures reaching 430 °C, acted as amorphous carbon coatings, while the total amount and uniformity of the carbon content could be controlled by the number of times SGCWs were applied. The developed carbon coatings were used as templates for MnO₂ shells to synthesize core-shell Ni@MnO₂ hybrid foams as binder-free supercapacitor electrodes. The core-shell Ni@MnO₂ foams fabricated by applying SGCWs three times exhibited a high specific capacitance of up to 660 F g^-1 and stable capacitance retention (∼95.4% over more than 10 000 cycles) because of their lower serial resistance and optimal diffusion during the redox reaction. This tunable fabrication method using SGCWs in a vacuum-free, open-air environment enables the synthesis of scalable carbon coatings on metal- or ceramic-based foams for electrochemical applications.