Al-doped Ti4O7 with superior oxidation resistance and optical stability for high-temperature solar-thermal applications

Magnéli-phase Ti 4 O 7 exhibits broadband photothermal conversion but suffers from rapid oxidation to optically inactive TiO 2 , severely restricting its deployment in high-temperature solar-thermal systems. Here, we demonstrate that Al doping provides an effective dual-function strategy to simultaneously enhance the oxidation resistance and optical stability of Ti 4 O 7 while maintaining its intrinsic photothermal performance. Al-doped Ti 4 O 7 powders (0–10 at. %) were synthesized via hydrogen reduction, and their structural evolution, oxidation kinetics, and spectral responses were systematically evaluated under controlled oxidative environments (300–500 °C, 2–10 h). Al 3+ incorporation induces lattice distortion and electronic localization, which increase oxygen migration barriers and suppress electron-assisted oxidation. During annealing, Al–O–Ti species progressively transform into Al–O–Al–enriched surface layers, forming a robust diffusion barrier that significantly retards the Ti 4 O 7  → TiO 2 conversion. As a result, the 10 at. % Al-doped sample retains a high solar absorptance of 95.8% after 400 °C/10 h oxidation, outperforming undoped Ti 4 O 7 (92.2%). Moreover, controlled oxidation produces Ti 4 O 7 @TiO 2 core–shell structures with statistically enhanced near-infrared absorption arising from multiple interfacial reflections and scattering–induced phase accumulation. Kinetic analysis confirms reduced oxidation rates and increased activation barriers across the full temperature window. These results establish Al-doped Ti 4 O 7 as a durable, thermally stable photothermal material suitable for solar selective absorbing coatings, concentrated solar power receivers, and other high-temperature chemical engineering processes requiring long-term optical and structural robustness.