Turning Waste into Value: Photocatalytic Conversion of Methane to Methanol Using NiO/TiO ₂ Catalyst Derived from Spent Ni–Cd Batteries

The selective conversion of methane to methanol under mild conditions remains a major challenge due to the high stability of the C–H bond and the propensity for overoxidation. Herein, NiO/TiO 2 photocatalysts were synthesized using both commercial nickel precursors and nickel recovered from spent Ni–Cd batteries, providing a sustainable pathway that integrates methane valorization with battery‐metal recycling. The battery‐derived catalysts PB1 and TB1 achieved methanol formation rates of 2.66 and 6.36 mmol g −1 ·h −1 , respectively, comparable to those of the commercial counterparts PC1 (2.38 mmol g −1 ·h −1 ) and TC1 (7.31 mmol g −1 ·h −1 ), demonstrating that recycled nickel can effectively replace commercial nickel without performance loss. Synthesized TiO 2 ‐based catalysts consistently outperformed P25‐based materials, and increasing Ni loading correlated positively with methanol formation rate, underscoring the importance of Ni‐induced defect engineering. Structural and spectroscopic analyses confirmed preservation of the anatase phase alongside the formation of Ti 3+ and oxygen vacancies, which suppressed electron–hole recombination. Density functional theory calculations revealed that methane activation proceeds via a low‐barrier homolytic C–H cleavage pathway on Ni–O sites in the presence of surface hydroxyl species, stabilizing methyl intermediates and favoring selective methanol formation. Ultimately, the combined experimental and theoretical results establish recycled Ni‐modified TiO 2 as a sustainable and mechanistically rational photocatalyst for selective methane‐to‐methanol conversion.