Understanding the Nature of Ammonia Treatment to Synthesize Oxygen Vacancy-Enriched Transition Metal Oxides

Oxygen vacancies (OVs) have emerged as an important strategy to modulate the electronic structures, conductivity, and catalytic performance of transition metal oxides (TMOs). A few studies reported that OVs could be formed in N-doped TMOs during ammonia treatment. However, the OV-enriched TMOs without N-doping obtained through ammonia treatment are still unreported and their mechanism is unclear. Herein, we adopt experimental and theoretical investigations to demonstrate the mechanism of ammonia treatment. Based on this mechanism, we develop a facile method to synthesize OV-enriched blue WO3−x porous nanorods (OBWPN) without N-doping. OBWPN exhibit promising performance for photothermal reduction of CO2-H2O to CH4 without any external cocatalysts or sacrificial agents. In addition, the low-temperature ammonia-assisted reduction treatment is a universal strategy to generate OVs in other TMOs with enhanced performance of photocatalytic hydrogen generation. This work is significant for understanding the nature of ammonia treatment and promoting the wide application of OV-enriched TMOs.