Investigation on the electroreduction of nitrate in alkaline media for value-added products

Abstract

As a harmful chemical, nitrate has been increasingly found in agricultural runoff and industrial wastes. The pollution of nitrate is directly responsible for rampant eutrophication in natural waters as well as other environmental problems. The waste nitrate also finds its way to drinking water. The intake of excess nitrate has been linked to severe health issues, specific cancers, and birth defects. Traditional mitigation technique of nitrate pollution is through the process of biological denitrification turning nitrate into unharmful nitrogen gas with no economic value. An alternative approach is through electroreduction of converting nitrate into value-added products such as ammonia, a substance used in fertilizer, chemical, or fuel; another words “turning trash into treasure”. This research program critically examines the electrochemical reduction of nitrate in alkaline media on a series of metal surfaces with ammonia and nitrite as the two leading value-added nitrogen-centric products. By means of accurate product detection and reliable constant-potential electrolysis, the catalytic activity and product selectivity have been comprehensively investigated. We have discovered the metal-nitrogen binding energy plays a key role in governing the activity of nitrate electroreduction on those metal surfaces. We have also identified the cobalt as the most active metal surface for ammonia formation. A systematic study was conducted on cobalt surface in comparison with copper (common metal for nitrite reduction) and rhenium under different cathode potentials, revealing a broad potential window of operation. Our research advanced the scientific understanding of the electroreduction of nitrate, and therefore lays the foundation for future materials development and real-world applications.