Electrochemical nitrate reduction for green ammonia production: assessing the impact of real water composition for energy carrier applications

Ammonia (NH3) has historically been an indispensable chemical, mainly as fertilizer. Recently, it has gained attention as a carbon-free energy carrier. Global ammonia production is dominated by the Haber-Bosch process, which is energy-intensive and generates significant CO2 emissions. To keep global warming below 1.5 °C, as called for in the Paris Agreement, emissions need to be reduced by 45% by 2030 and reach net zero by 2050. As a result, developing a sustainable and efficient pathway for NH3 synthesis is urgent. On the other hand, nitrates pollution in water bodies is a growing global concern. Nitrogen is a crucial element for life, but the intensification of human activities in agriculture leads to water contamination and a decline in water quality. When nitrate concentrations exceed a certain threshold, they can be harmful to human health. The electrocatalytic nitrate reduction reaction (NO3RR) offers a pathway to achieve both ammonia production and water denitrification. This work aims to demonstrate the feasibility of ammonia production from electrocatalytic reduction of nitrates contained in real wastewater. For that purpose, the influence of various elements commonly found in real waters on NO3RR was first evaluated. Then a simulated brackish water reverse osmosis brine, representative of real conditions, was used as the electrolyte in the NO3RR process. The efficiency was markedly lower when real brackish water was used as the electrolyte, highlighting the challenges associated with complex water matrices.