Direct electrosynthesis of methylamine from carbon dioxide and nitrate

The electrochemical reduction of carbon dioxide is an appealing technology that stores renewable electricity in the chemical form and has the potential to transform the way carbon fuels are utilized today. While there have been successes in the electrosynthesis of alkanes, alkenes and alcohols, access to organonitrogen molecules such as alkylamines remains largely beyond the reach of current electrocatalysis. Here we report the first electrochemical reaction that converts carbon dioxide and nitrate to methylamine in aqueous media under ambient conditions catalysed by a cobalt β-tetraaminophthalocyanine molecular catalyst supported on carbon nanotubes. The overall reaction, involving the transfer of 14 electrons and 15 protons to form each methylamine molecule, is an eight-step catalytic cascade process enabled by the coupling of two reactive intermediates near the catalyst surface. The key C–N bond-forming step is found to be the spillover of hydroxylamine from nitrate reduction and its subsequent condensation with formaldehyde from carbon dioxide reduction. This study provides a successful example of sustainable alkylamine synthesis from inorganic carbon and nitrogen wastes, which could contribute to greenhouse gas mitigation for a carbon-neutral future. The electroreduction of CO2 provides a sustainable pathway to value-added fuels and chemicals. Here the authors show a cascade reaction that yields methylamine from CO2 and nitrate. With detailed insight into the multistep catalytic process, the current findings further push the boundaries of this technology.