Urea synthesis via electrocatalytic oxidative coupling of CO with NH3 on Pt

Abstract

Electrochemical conversion of CO to chemicals containing C–N bonds offers an appealing route to store renewable electricity and mitigate CO2 emission, as CO2 can be efficiently transformed to CO. Previous electrocatalysis research has primarily focused on cathodic reactions, which are impeded by the competing hydrogen evolution reaction and limited electron efficiency. Here we present a urea synthesis approach via electrocatalytic oxidative coupling between CO and NH3 on commercial Pt catalysts. We demonstrate an optimal selectivity of approximately 70% for urea and remain above 50% throughout a wide potential window with an electrocatalytic C–N bond formation rate of up to 100 mmol h−1 gcatalyst−1. In mechanistic investigations, we propose that the oxidative coupling of CO and NH3 on Pt leads to cyanate formation, followed by the Wöhler reaction to form urea. This approach offers a practical route for urea production with high electron efficiency by enabling Pt-catalysed reactions between CO and NH3. Electrocatalytic urea formation most commonly involves the co-reduction of NOx species with CO2. This limits overall energy efficiency as commodity-scale NOx is produced from N2 via NH3. The swings in nitrogen oxidation state can be minimized through direct oxidative electrocatalytic reaction of CO and NH3 to urea, as shown in this study.