Crystal-phase-regulated oxidation of MnO2 for tailoring the structure and microwave absorption of polypyrrole

Facing severe electromagnetic interference and radar detection threats, efficient lightweight microwave absorbers are highly demanded. In this work, α-, β- and γ-MnO2 nanorods were adopted as self-sacrificial oxidants to prepare pure-phase polypyrrole (PPy) via in-situ chemical oxidative polymerization. The effects of MnO2 intrinsic oxidizability on the microstructure, electromagnetic properties and microwave absorption behaviors of PPy were systematically explored. Results show that α-MnO2-derived AM-PPy achieves optimal absorption performance at a low filling ratio of 10%, with a minimum reflection loss (RLmin) of −47.41 dB and an effective absorption bandwidth (EAB) of 7.67 GHz. First-principles calculations verify that β-MnO2 with weak oxidizability induces the growth of long conjugated PPy chains to raise dielectric constants, yet excessive dielectric value deteriorates impedance matching and absorption capacity. Radar cross-section simulation further proves the excellent stealth potential of AM-PPy. This study clarifies the crystal phase regulation mechanism of MnO2 toward PPy, and provides a feasible strategy for the rational design of high-performance PPy-based microwave absorbing materials.