Band gap and oxygen vacancy engineering of honeycomb‐like CuFe 2 O 4 spinels toward enhanced high infrared emissivity

Abstract Recently, copper ferrites have acquired widespread attraction in high infrared radiation fields owing to their remarkable cost efficiency. However, to achieve broader applications under various operating conditions, it is essential to further improve the infrared emissivity, particularly at high temperatures. Herein, the Ni‐doped CuFe 2 O 4 (NCFO) honeycomb‐like frameworks, which are constructed with single‐crystal nano‐subunits, are successfully fabricated via the scalable sol–gel avenue. The unique porous honeycomb framework endows NCFO with enhanced infrared absorption and relieves the stress between coatings and substrates meanwhile. With both band gap and oxygen vacancy (OV) engineering of CuFe 2 O 4 itself via smart Ni doping, a maximum lattice strain, the richest OVs, and the narrowest band gap (∼1.63 eV) are simultaneously achieved for the CuFe 2 O 4 with 15% Ni doping (denoted as CNFO‐15). Benefiting from the synergy of these external and intrinsic contributions, the CNFO‐15 possesses an ultrahigh infrared emissivity (∼0.975) in the wavelength range of 3–5 µm at a test temperature of 800°C. Moreover, the CNFO‐15‐based coating displays superior infrared radiation performance with outstanding high‐temperature resistance. More meaningfully, the constructive design here will provide a distinctive perspective for future large‐scale fabrication of advanced high‐infrared‐emissivity coatings.