Electrochemical system and catalyst development for ammonia production from nitric oxide in flue gas

Abstract

Electrochemical conversion of nitric oxide (NO) to ammonia (NH3) provides a breakthrough way to transform a harmful air pollutant into a value-added resource. Today’s development of NO electroreduction remains hindered by the poor solubility of NO in aqueous electrolytes, and it requires the use of highly concentrated NO gas. Here, we introduce a NO electrolyzer with gas diffusion electrode (GDE) using dilute NO as a feed gas to significantly improve the NO mass transport. However, although the gas diffusion electrode improved the rate of delivering low-concentration NO to the catalyst layer, it promoted side reactions by changing the NO coverage on the catalyst surface, thereby lowering the product selectivity of the reduction reaction to ammonia. Therefore, in order to improve product selectivity, we incorporated nanoscale zero-valent iron (NZVI) to carbon, and density functional theory revealed the effective breakage of N–O bond of H2NO intermediate on iron, thereby increasing the ammonia selectivity. The catalyst exhibited 165 mAcm-2 of NH3 partial current density through further optimization of the operating parameters at the condition of 10% NO and 0.5 M H2SO4 electrolyte. In addition, the copper catalyst, which has recently been reported to have high activity for the NO reduction reaction, was investigated, and the shape evolution of the catalyst during the reaction was discovered, and its effects and causes were investigated. Through this doctoral thesis research, an innovative method to convert harmful air pollutants into value-added resources was demonstrated, and this is expected to change the paradigm for sustainable environmental processes to offer one avenue to treat air pollutant and produce valuable NH3 simultaneously.