Full‐Lifecycle Biocarbon Foam through Multiscale Pore Engineering Toward Ultra‐High Electromagnetic Absorption

Abstract Conventional plastic foams are usually produced by fossil‐fuel‐derived polymers, causing serious environmental pollution. Herein, a sustainable multifunctional biocarbon foam is developed through a multiscale pore engineering strategy, involving the physical cross‐linking of biocarbon with cellulose and subsequent ambient drying. This eco‐friendly foam exhibits superior electromagnetic shielding effectiveness (up to 80.3 dB), good thermal insulation (0.12 W m ⁻¹ K ⁻¹ ), and mechanical robustness. The foam's multiscale porous structure, which includes graphene‐like carbon and nanopores for dielectric loss along with micro‐ to macro‐pores for multiple internal reflections, achieves ultra‐high electromagnetic absorption of ≈99.7% at 11.3 GHz, featuring an obvious advantage over traditional reflecting‐dominated shielding materials such as metals. The biocarbon foam also offers a significantly lower environmental impact compared to petrochemical‐based foams, with the potential for waste to be used as a biofertilizer to promote plant growth and carbon sequestration. This study presents a full lifecycle approach to multifunctional biocarbon foams, offering a sustainable alternative to traditional petrochemical‐based foam materials.