Corn silk-derived biomass carbon materials for low-frequency microwave absorption and energy storage

Biomass carbon (BC) materials derived from agricultural waste have shown great potential in microwave absorption (MA). However, current research mainly focuses on high-frequency (8-18 GHz) MA, and much less effort has been spent on low-frequency (2-8 GHz) MA and other important functionalities such as energy storage. Herein, corn silk rich in carbon is utilized to prepare BC materials with uniform pores and large specific surface area through a straightforward chemical activation and carbonization process. Attributed to its optimized impedance matching, interfacial polarization and (N and O) heteroatom-induced dipole polarization, the optimal sample exhibits superior low-frequency MA capability, including a strong reflection loss (RL) of -75 dB at 6.88 GHz, an effective absorption bandwidth (EAB, RL ≤ -10 dB) down to 2.8 GHz, and excellent radar cross-section reduction. Furthermore, it achieves a high initial discharge specific capacity of 1015.54 mA·h g^-1 and stable cycling performance at 0.5 A g^-1 in lithium-ion batteries owing to its heteroatom-rich porous structure with a large specific surface area. Our study offers a simple and low-cost way to fabricate high-performance multifunctional BC materials for low-frequency MA and lithium-ion energy storage.