Template‐Free Gradient Selective Etching of Porous Carbon Nanospheres: Synergistic Dielectric Loss Optimization and Bifunctional Microwave Absorption‐Corrosion Resistance Integration

Abstract The development of microwave‐absorbing coatings for saline environments confronts dual challenges: dielectric loss optimization and porous carbon corrosion resistance. A solvent‐mediated dynamic etching strategy achieving dual structural synergy is proposed. Acetone‐regulated pore architecture enables template‐free gradient etching, achieving tunable electromagnetic parameters and optimized absorption performance through pore size differentiation in nitrogen‐doped 3D networks. In situ surface deoxygenation constructs hierarchical superhydrophobic micropores, decoupling pore topology from moisture adsorption. By bridging atomic‐scale defect engineering and macroscopic interface optimization, a microstructure‐mediated dielectric regulation paradigm is established. The optimized hollow porous carbon nanoparticles etched by 130 mL of acetone (HPCNs‐130) demonstrate exceptional performance with −16.0 dB reflection loss at 2.78 mm thickness and 2.28 GHz bandwidth at 4.61 mm. Crucially, 48 h salt spray tests confirm superior corrosion resistance versus uncoated substrates. The coating significantly reduces the corrosion current from 25.44 to 0.53 µA cm ^{− 2} , achieving a corrosion inhibition efficiency of 97.9%. This work proposes a novel solvent‐mediated dynamic etching strategy, enabling template‐free and gradient‐controlled pore architecture, overcoming template‐dependent structural limitations. By bridging atomic‐scale defect engineering and macroscopic interface optimization, a structure‐function synergy paradigm is demonstrated that concurrently addresses electromagnetic attenuation and electrochemical degradation, providing transformative solutions for marine infrastructure protection.