Pulsed co-electrolysis of carbon dioxide and nitrate for sustainable urea synthesis

The urea industry is energy intensive and responsible for high levels of carbon emissions. Electrocatalytic co-reduction of carbon dioxide (CO2) and nitrate (NO3−) powered by renewable energy offers an alternative and sustainable synthetic pathway to this chemical that is vital in agriculture, chemical engineering and other fields, but the yield rate cannot compete with the state-of-the-art petrochemical processes. Here we show a urea electrosynthesis route using an iron tetraphenylporphyrin molecular electrocatalyst that delivers a maximum Faradaic efficiency of 27.70% for urea while suppressing the competing hydrogen evolution reaction. At the heart of our strategy is electrolysis under pulsed potentials between −0.2 and −0.8 V versus the reversible hydrogen electrode, which increases the local concentration of CO2/NO3− but reduces the local pH to enrich *CO and *NH2 intermediates favoured by C–N coupling. Importantly, our strategy can be applied to more catalyst systems such as ZnO and PdCu, and save more than 41% energy consumption compared with static co-electrolysis, with PdCu enabling a maximum urea Faradaic efficiency of 70.36% for pulsed electrolysis. Our work opens an avenue for efficient urea production and provides insights into the role of the local reaction environment, which can inform the rational design of electrocatalysts.