Sikirić M., Choquet P., Philippe A.M., Valle N., Hadler K., Bulou S.
Vacuum, vol. 244, art. no. 114952, 2026
The reduction of titanium dioxide using H<sub>2</sub> plasma is demonstrated as a viable pathway for oxygen extraction and possible metal production in ISRU. In this study, TiO<sub>2</sub> thin films representing the Ti-bearing phase of ilmenite were exposed to low-pressure Electron Cyclotron Wave Resonance (ECWR) hydrogen plasma, achieving substantial oxygen release at temperatures significantly lower than conventional thermal reduction. Advanced characterisation (TEM, EELS, SIMS) revealed stepwise partial reduction of TiO<sub>2</sub>, progressing through sub-stoichiometric oxides toward Ti<sub>2</sub>O<sub>3</sub>. Substrate heating experiments showed that the activation barrier is reached at ∼500 °C, where reduction kinetics accelerated and extent of conversion increased. Microstructural analysis revealed plasma-induced porosity and cracking, associated with the propagation of a reduction front through the film highlighting a plasma-specific microstructural activation that enhances bulk reduction. While full conversion to metallic titanium remains challenging, the ECWR plasma promoted the formation of intermediate lower oxides, suggesting that low-pressure plasma-assisted reduction could require substantially less energy and hydrogen per unit oxygen liberated than conventional hydrogen thermal reduction. These findings highlight hydrogen plasma reduction as a promising and energy-efficient approach for ISRU lunar oxygen production while also offering potential benefits for sustainable industrial processes on Earth.
