Partially or fully reduced transition metal oxides show extraordinary electronic and catalytic properties but are usually prepared by high temperature reduction reactions. This study reports the systematic investigation of the fast mechanochemical reduction of rutile‐type TiO₂ and H‐Nb₂O₅ to their partially reduced black counterparts applying NaH and LiH as reducing agents. Milling time and oxide to reducing agent ratio show a large influence on the final amount of reduced metal ions in the materials. For both oxides LiH shows a higher reducing potential than NaH. An intercalation of Li⁺ into the structure of the oxides was proven by PXRD and subsequent Rietveld refinements as well as ⁶Li solid‐state NMR spectroscopy. The products showed a decreased band gap and the presence of unpaired electrons as observed by EPR spectroscopy, proving the successful reduction of Ti⁴⁺ and Nb⁵⁺. Furthermore, the developed material exhibits a significantly enhanced photocatalytic performance towards the degradation of methylene blue compared to the pristine oxides. The presented method is a general, time efficient and simple method to obtain reduced transition metal oxides.

Partial reduction of transition metal oxides via defect engineering is a promising strategy to enhance their electronic and photocatalytic properties. In this study, we systematically explored the mechanochemical reduction of Nb₂O₅ using LiBH₄ and NaBH₄ as reducing agents. Electron paramagnetic resonance (EPR) spectroscopy confirmed a successful partial reduction of the oxide, as seen by the presence of unpaired electrons. Interestingly, larger hydride concentrations did not necessarily enable a higher degree of reduction as large amounts of boron hydrides acted as a buffer material and thus hindered the effective transfer of mechanical energy. Powder X-ray diffraction (PXRD) and ⁷Li solid-state NMR spectroscopy indicated the intercalation of Li⁺ into the Nb₂O₅ lattice. Raman spectroscopy further revealed the increased structural disorder, while optical measurements showed a decreased band gap compared with pristine Nb₂O₅. The partially reduced samples showed significantly enhanced photocatalytic performance for methylene blue degradation relative to the unmodified oxides.

Partial reduction of transition metal oxides via defect engineering is a promising strategy to enhance their electronic and photocatalytic properties. In this study, we systematically explore the mechanochemical reduction of Nb2O5 using LiBH4 and NaBH4 as reducing agents. Electron paramagnetic resonance (EPR) spectroscopy confirms a successful partial reduction of the oxide, as seen by the presence of unpaired electrons. Interestingly, larger hydride concentrations do not necessarily enable a higher degree of reduction as large amounts of the boron hydrides act as a buffer material and thus hinder the effective transfer of mechanical energy. Powder X-ray diffraction (PXRD) and 7Li solid-state NMR spectroscopy indicate the intercalation of Li+ into the Nb2O5 lattice. Raman spectroscopy further reveals the increased structural disorder, while optical measurements show a decreased band gap compared to pristine Nb2O5. The partially reduced samples show significantly enhanced photocatalytic performance for methylene blue degradation relative to the unmodified oxides.

Vanadium oxides and alkali metal vanadates are promising electrode materials for electrochemical energy storage owing to their ability to access multiple oxidation states. In this study, mechanochemical reduction of V₂O₅ with alkali metal hydrides is explored as a facile route to obtain reduced vanadium oxide phases. Sodium hydride enables the rapid formation of mixed sodium vanadium oxide phases at room temperature, proceeding in a self-propagating manner after only a short milling period. To assess the generality of this approach, lithium hydride was evaluated as an alternative reducing agent and exhibited comparable reaction behavior and product distributions. Complementary theoretical calculations indicate that the corresponding reductions with elemental sodium and lithium are thermodynamically more favorable, displaying lower reaction enthalpies. This prediction is experimentally corroborated by the instantaneous ignition observed when elemental metals are used. Rietveld refinement reveals that all investigated reducing agents follow similar reaction pathways, yielding comparable mixtures of alkali metal vanadium oxides with consistent main phases. However, the use of highly ductile sodium metal results in significant mixing limitations, which can be mitigated only through cryogenic milling. These findings highlight mechanochemical reduction with alkali metal hydrides as a robust and practical strategy, particularly for systems in which metal ductility limits process efficiency, despite the associated risk of hydrogen evolution.