Optical sensors for in situ real-time detection of ammonia

Abstract

The nitrate reduction reaction (NO₃RR) is a highly promising method for ammonia production. It contributes to advancing the production and application of ammonia as an industrial raw material and green energy. Currently, the evaluation of catalyst performance for electrocatalytic ammonia synthesis mainly relies on static indicators such as Faraday efficiency, ammonia yield per unit area, and overpotential. However, the dynamic in situ description of ammonia generation on the electrode surface is lacking. We propose an ammonia concentration sensor based on fluorescence excitation. Through in situ real-time detection of the reaction, the changes in ammonia concentration at corresponding times in different regions on the electrode surface were calculated, thereby further elucidating the mechanism of the entire electroreduction reaction process. Copper foam was used as the working electrode to verify the design of the sensor. This sensor was then applied to a Co-based/Cu electrode synthesized by local electrodeposition. Cobalt-based materials exhibited better catalytic performance than copper and confirmed the excellent spatial resolution capability of the sensor. Finally, using this sensor, a comparison was made between several common foam metal substrates and their corresponding ammonia production rates after electrodeposition modification, demonstrating the capability of the sensor in quantitative analyses and electrode screening. This sensor provides a new approach for studying the reaction mechanism of the final ammonia product in NO₃RR as well as the screening and design of catalysts.