Development of activated carbon from hemp hurd for EMI shielding and supercapacitors via one-step microwave pyrolysis without inert gas

This study introduces a novel method to produce multifunctional activated carbon from hemp using one-step microwave-assisted wet pyrolysis without inert gas. Unlike traditional processes that rely on microwave absorbers like SiC or graphite, sulfuric acid was employed as a catalyst, dehydration agent, activator, and microwave absorber due to its polar nature in this study. This approach significantly reduces volatile organic compound emissions and limits greenhouse gas release. Once carbonization begins, the material itself becomes a microwave absorber, accelerating the process through a positive feedback loop, greatly enhancing pyrolysis efficiency. The resulting activated carbon was tested for electromagnetic interference (EMI) shielding and supercapacitor applications. The highest EMI shielding effectiveness was measured as 36.83 dB at 1 GHz, surpassing the 20 dB standard (FTTS-FA-003) for moderate industrial use. Supercapacitor performance was also impressive, with a specific capacitance of 436.71 Fg⁻¹, energy density of 136.28 Wh kg⁻¹, and power density of 395 W kg⁻¹, comparable to commercial alternatives. The BET surface area was measured at 484.36 m²/g, which, although lower than some reported values of 1000–2000 m²/g, was compensated by electronegative oxygen groups that significantly enhanced both EMI shielding and supercapacitor performance. Overall, these findings demonstrate the effectiveness of this sustainable method for producing high-performance multifunctional carbon materials, with strong potential for applications in energy storage and EMI shielding.