Thermal‐Assisted Photosynthesis of Nitric Acid From Air

A novel Ir-WO₃ with cation vacancy chains is fabricated and utilized as a highly efficient catalyst for nitrogen oxidation under an innovative discontinuous light illumination strategy with a record NO₃ ⁻ yield of 381.21 µmol g⁻¹ h⁻¹. Then, a novel •OH assisted nitrogen activation mechanism is proposed based on the identification of crucial N₂O intermediate and operando experiments.

Abstract

Photocatalytic nitrogen oxidation reactions has emerged as promising techniques for air-based nitrate synthesis, bolstering sustainable nitrogen fixation in industrial chains centered around nitrates. However, significant disparities in orbital energy levels impose constraints on N₂ conversion, highlighting the pivotal role of nitrogen activation, particularly in oxygen-rich environments. Herein, a novel Ir-WO₃ catalyst with cation vacancy chains is fabricated and utilized as a highly efficient catalyst for thermal-assisted nitrogen oxidation under an innovative discontinuous light illumination strategy. Remarkably, an unexpected NO₃ ⁻ yield of 381.21 µmol g⁻¹ h⁻¹ is achieved, marking a 10.4-fold increase compared to regular continuous light illumination. This exceptional performance is attributed to the unique structure and discontinuous light illumination, which lowered the energy barrier of the rate-determining step for forming *NN(OH) intermediates and enhanced the abundance of •OH. Furthermore, a novel •OH assisted nitrogen activation mechanism is proposed based on the identification of crucial N₂O intermediate and operando experiments. This work offers novel insights into free radicals-based photocatalytic conversion processes and also presents a potential nitrate synthesis pathway for nitrates-centric industrial nitrogen fixation chains.