Dual built-in electric field engineering in heterostructure nickel-cobalt bimetallic composites for boosted electromagnetic energy dissipation

Built-in electric fields (BIEF), engineered via space charge manipulation, represent an effective strategy for enhance electromagnetic loss. However, single BIEF fail to reconcile the impedance matching and strong electromagnetic attenuation across broad frequency spectra, resulting in limited effective absorption bandwidth (EAB). To address this, dual-BIEF are constructed utilizing an asymmetric gradient electric field structure and multi-polarization center coordination to achieve high-efficiency broad EAB. Herein, heterostructure Ni-Co bimetallic nanocomposites (Ni_0.5Co_0.5@NiCoO₂/NCP) are constructed via Ni-Co-based nanocomposites (NiCoO₂ and Ni_0.5Co_0.5) integrated with nitrogen-doped nanoporous carbon (NCP). This configuration forms dual heterojunctions the NCP-NiCoO₂-semiconductor heterojunction and the NiCoO₂-Ni_0.5Co_0.5 Mott-Schottky heterojunction—forming the dual-BIEF system. The superposed dual-BIEF drives charge-pumping dynamics facilitating oriented transfer and transition of charges that strengthen interfacial polarization and reduced relaxation times. Theoretical calculations confirm this system simultaneously modulates conductivity, intensifies polarization relaxation, promotes charge separation, and optimizes dipole distribution. Dielectric loss from semiconductor junctions dominates the low-frequency regime, while conductive loss via Mott-Schottky junctions prevails at high frequencies. Thus, the Ni_0.5Co_0.5@NiCoO₂/NCP achieves excellent microwave absorption with a remarkable minimum reflection loss of −51.5 ​dB, and an EAB of 6.4 ​GHz at 2.8 ​mm thickness. This work establishes a dual-BIEF strategy for effectively engineering high-performance electromagnetic wave absorption materials.