Co–Ni synergistic catalysis enabling gradient mesoporous carbon electrodes for high-performance supercapacitors

The mismatch between micropore sizes and electrolyte ion dimensions in supercapacitors represents a critical bottleneck limiting their performance enhancement. In this work, we employed Co and Ni bimetallic catalysis, using phenolic resin as the carbon precursor, to synthesize hierarchical micro/mesoporous N-doped hollow carbon materials. This approach mitigates the mismatch between ion diffusion pathways and ion sizes, while preventing pore collapse during high-temperature carbonization, thereby significantly enhancing electrical conductivity, graphitization degree, and wettability. Consequently, the resulting material achieves a maximum specific capacitance of 116.7 F g⁻¹ at 0.5 A g⁻¹, exhibits excellent cycling stability (81 % capacitance retention after 1000 charge-discharge cycles at 1 A g⁻¹), and maintains 100 % Coulombic efficiency. These performance metrics surpass those of carbon electrodes catalyzed by single Co or Ni metals, as well as previously reported phenolic resin-based carbon materials. This strategy enables the development of high-performance supercapacitor electrode materials tailored for aqueous electrolyte systems.