Heating-Rate Controlled Microwave Co-Pyrolysis for Synergistically Doped Carbon Electrode Materials

Biomass-derived carbons are widely recognized as sustainable and low-cost electrode materials for energy storage, but precise control over their structural evolution and performance remains a significant challenge. Microwave activation has been seen as an effective way to control carbons’ structure and performance parameters; however, limited research has quantified the activation mechanism, e.g., the influence of the average microwave heating rate on the key material properties. This study aims to develop a controllable microwave thermal copyrolysis route for synthesizing a self-doped porous carbon from sugar cane bagasse and peanut straw, where the average microwave heating rate was precisely regulated to control pore development, graphitization, and heteroatom incorporation. The experimental results show that a moderate heating rate of 35 °C min–1 is optimal for facilitating the synergy between KOH activation and gas release, leading to a high specific surface area (2453.8 m2 g–1), a balanced micro/mesoporous architecture, and uniform N/O codoping. Furthermore, this heating rate significantly enhances the electrode’s electrochemical performance, achieving a high specific capacitance of 340 F g–1, low resistance (0.256 Ω), and outstanding cycling stability (97.1% capacitance retention after 20,000 cycles). From a processing perspective, when considering the entire preparation route including carbonization and activation, the microwave-assisted process shows clear energy and cost advantages over the conventional muffle furnace method, with the total energy consumption of the latter being approximately 3.2 times higher and the unit cost per capacitance reduced by 61.2%. These findings highlight that controlling the microwave heating rate plays a crucial role in optimizing carbon microstructure and performance, and demonstrate the potential of microwave-assisted activation as an energy-efficient intensification step for converting agricultural residues into high-performance electrode materials for next-generation supercapacitors.