Electrochemical coreduction of nitrite and CO₂ in an ionic liquid system

Abstract

Environmental concerns and demand for sustainability drive investigations of electrochemical reduction of CO₂, N₂, and nitrogen pollutants. The simultaneous reduction of CO₂ and nitrite to generate urea tackles multiple issues while producing valuable products. Moreover, incorporating ionic liquids (ILs) improves catalytic performance and selectivity. This study investigates the performance of various catalysts, including cobalt and iron phthalocyanine, as well as Cu, Pd, Ir, MoS₂, TiO₂, and Rh nanoparticles, and graphene nanoplatelets in terms of urea production rates and yields. When a cobalt phthalocyanine catalyst was combined with a mixture of 1-butylpyridinium hexafluorophosphate (BuPyPF₆) and trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide (P₆₆₆₁₄NTf₂), the hydrophobic nature of the catalyst layer increased, resulting in higher faradaic efficiency (25% at –0.064 V vs RHE). Combining a commercial carbon-supported Cu catalyst with CoPc proved effective in increasing urea production rates, although it led to a decrease in faradaic efficiency. However, the application of carbon black as the supporting layer proved advantageous when graphene and TiO₂ as the catalyst supports were used. TiO₂, in particular, showed promise as both the catalyst and supporting material, achieving an impressive 71% urea yield when combined with CoPc. Fe (III) tetrasulfophthalocyanine, in conjunction with the mixed IL binder, exhibited a high urea production rate but low yield.