Impact of microwave-induced thermal shock on the structural evolution of biomass-derived porous carbon and the resulting promising electrochemical performance.

The compact lignocellulosic architecture of biomass severely restricts the diffusion of KOH into the precursor matrix, resulting in inefficient activation, excessive chemical consumption, and prolonged energy-intensive thermal treatment. Although microwave-assisted carbonization can accelerate biomass conversion, conventional multimode microwave systems often suffer from non-uniform electromagnetic field distribution, which limits controllable pore development. Herein, a single-mode Microwave-Induced Thermal Shock activation strategy, based on an IR-recorded rapid apparent heating response, was developed by integrating focused microwave irradiation with KOH chemical activation to achieve the one-step carbonization-activation of pine sawdust into biomass-derived porous carbon for high-performance supercapacitor electrodes. In this process, KOH serves not only as a chemical activating agent but also as a microwave absorber, enhancing the dielectric response of the biomass/KOH mixture and promoting efficient coupling with the concentrated microwave field. The rapid apparent heating response induced by single-mode microwave irradiation promotes volumetric heating, volatile release, pore opening, and simultaneous KOH etching of the carbon matrix, thereby overcoming the mass-transfer and heat-transfer limitations associated with conventional activation. Benefiting from this chemical-physical synergy, the carbonization-activation process was completed within only 3-21 min, which is substantially shorter than that required for conventional furnace-based thermal activation. Under a low activator-to-precursor mass ratio of 1:2, PWPC-800W-9min-0.5 achieved a high specific surface area of 1105.63 m2 g-1 and a hierarchical micro/mesoporous structure. PWPC-800W-18min-0.5 delivered a specific capacitance of 345.5 F g-1 at 0.5 A g-1 in a three-electrode system, while the assembled symmetric supercapacitor retained 97.56% of its initial capacitance after 10,000 cycles at 2 A g-1. The favorable electrochemical performance is attributed to the synergistic contribution of abundant micropores for charge storage, interconnected mesopores for rapid ion transport, and oxygen-containing defect sites for improved electrolyte wettability and interfacial charge transfer. This work demonstrates that single-mode Microwave-Induced Thermal Shock activation provides a rapid and activator-efficient route with potential energy-efficiency advantages for converting lignocellulosic waste into high-performance porous carbon electrodes.