An optical sensor for in situ real-time detection of intermediate products in nitrate reduction reactions†

The nitrate reduction reaction (NO₃RR) is a promising method for ammonia production, but detecting intermediate NO₂⁻in situ during the reaction is challenging. We propose a nitrite concentration sensor based on equivalent absorbance change, comprising a light, absorption, and imaging module, with a linear detection range of 0–1.4 mg L⁻¹. After optimizing the absorption module parameters and applying machine learning noise reduction, the detection limit is 0.0116 mg L⁻¹. Using foam copper as the working electrode, we achieved real-time monitoring of nitrite concentration on the electrode surface during NO₃RR, validating the sensor's design. When applied to Co Base/Cu electrodes synthesized via localized electrodeposition, the sensor shows significantly lower nitrite concentration in the electrodeposition area compared to the non-electrodeposition area during NO₃RR, indicating superior nitrite utilization by cobalt-based materials. This sensor offers a new approach for investigating NO₃RR mechanisms and designing catalysts.