Minimum conditions for accurate modeling of urea production via co-electrolysis

Co-electrolysis of carbon oxides and nitrogen oxides promise to simultaneously help restore the balance of the C and N cycles while producing valuable chemicals such as urea. However, co-electrolysis processes are still largely inefficient and numerous knowledge voids persist. Here, we provide a solid thermodynamic basis for modelling urea production via co-electrolysis. First, we determine the energetics of aqueous urea produced under electrochemical conditions based on experimental data, which enables an accurate assessment of equilibrium potentials and overpotentials. Next, we use density functional theory (DFT) calculations to model various co-electrolysis reactions producing urea. The calculated reaction free energies deviate significantly from experimental values for well-known GGA, meta-GGA and hybrid functionals. These deviations stem from errors in the DFT-calculated energies of molecular reactants and products. In particular, the error for urea is approximately -0.25 +/- 0.10 eV. Finally, we show that all these errors introduce large inconsistencies in the calculated free-energy diagrams of urea production via co-electrolysis, such that gas-phase corrections are strongly advised. Co-electrolysis of nitrogen oxides and carbon oxides has been studied for over two decades but remains largely inefficient with numerous persisting knowledge voids. Here, the authors report a thermodynamic basis for modelling urea production via co-electrolysis using several exchange-correlation functionals, highlighting the importance of gas-phase error assessment in computational electrocatalysis.

Automated summary

This study provides a thermodynamic basis for modeling urea production via co-electrolysis of carbon oxides and nitrogen oxides. The authors determine the energetics of aqueous urea under electrochemical conditions and use density functional theory calculations to model co-electrolysis reactions. They find significant deviations between calculated reaction energies and experimental values due to errors in the DFT calculations and emphasize the need for gas-phase corrections.