Broadband light-absorbing ceramic cellular structures fabricated by 3D printing and sintering with oxide coatings

Functional oxide surface coatings on ceramic three-dimensional (3D) structures are pivotal for imparting tailored optical, thermal, and chemical functionality to complex architectures in solar energy and other high-end applications. Conventional ceramic 3D printing typically yields a single material, limiting multifunctionality and motivating ceramic composite architectures that integrate complementary properties. Achieving conformal and thermally stable oxide coatings on 3D-printed, high-surface-area ceramic cellular structures is highly desired, though challenging. This study presents a robust strategy for fabricating solar-absorbing CuO and iron-oxide (Fe₃O₄/Fe₂O₃) coatings on sintered Al₂O₃ cellular substrates to achieve high broadband absorptance across the UV–vis–NIR spectrum, which is corroborated by the Monte Carlo Ray Tracing (MCRT) simulation. With these coatings, average solar absorptance is boosted over 80% from 16.72% for bare Al₂O₃, demonstrating significant optical gains. The broadband absorption is mainly attributed to the strong intrinsic absorption of the oxide coatings, further enhanced by volumetric scattering within porous microstructure. High average absorptance at an operation temperature over 1000 °C demonstrates the durability and thermal stability of refractory coatings. Overall, the results demonstrate that controlled thermal processing is an effective route to highly absorbing, thermally stable oxide coatings on 3D-printed ceramic structures for concentrated solar thermal and photocatalytic systems.