Methanol is an attractive liquid hydrogen carrier, but conventional methanol steam reforming typically requires high temperatures and often relies on precious-metal catalysts. We wondered whether a simple metal oxide could be engineered to harvest light and drive this reaction more efficiently. By using a room-temperature lithium-reduction strategy, we introduced oxygen vacancies into In₂O₃, increasing its free-carrier concentration and giving rise to a broad near-infrared plasmon-like response.

The optimized defective In₂O₃ achieved a hydrogen production rate of 214 μmol gcat⁻¹ s⁻¹ under full-spectrum irradiation, together with high CO₂ selectivity and stable performance over 40 cycles. More importantly, matched-temperature controls showed that photothermal heating alone could not explain the high activity: the apparent activation energy decreased from 75.7 to 27.8 kJ mol⁻¹ under illumination.

Combining in-situ spectroscopy and theoretical calculations, we found that oxygen vacancies not only reshape the reaction pathway but also create an electronic environment that enables light-generated carriers to facilitate key dehydrogenation steps. Our work suggests that defect engineering can turn conventional metal oxides into non-noble-metal plasmonic catalysts, offering a new strategy for light-assisted hydrogen production and solar-to-chemical conversion.