Assembly of an actinide-uranium single atom catalyst on defective MXenes for efficient NO electroreduction

Abstract

The research on actinide-uranium single atom catalysts is particularly crucial in small pollutant molecule reduction due to the unique f orbitals of uranium with adjustable oxidation states. This work screens a series of actinide-uranium single atom catalyst embedded MXene monolayers with oxygen vacancies (UO₂@MXene, MXene = Ti₂CO₂, V₂CO₂, Cr₂CO₂, Zr₂CO₂, Nb₂CO₂ and Mo₂CO₂) for product selectivity in electrocatalytic NO reduction (ENOR) by well defined ab initio calculations. Our results indicate that the change from higher oxidation state U(VI) to sparingly soluble low valent U species anchored O-defective MXene surfaces when the model of uranyl adsorbate approached O vacancies of MXenes, which can overcome the limitation of catalytic performance of actinide metal centers. Furthermore, their efficiency for the electrochemical NO reduction reaction to NH₃ was evaluated. Among all actinide-uranium single atom catalysts, UO₂@Nb₂CO₂ exhibits the best activity and selectivity in NO reduction to NH₃, characterized by the lowest theoretical limiting potential of −0.14 V. Additionally, the constant-potential method (CPM) was performed to explore pH-dependent catalytic activity of UO₂@Nb₂CO₂. The findings indicate that the onset potential is −0.228 V vs. RHE at pH = 1, which is lower than 0.305 V vs. RHE at pH = 13, which suggests that the acid environment is relatively favorable for ENOR on UO₂@Nb₂CO₂. This work leverages environmental remediation and electro-catalytic reaction in an actinide-uranium complex, offering a novel approach to establish a theoretical framework for the most effective strategies of NH₃ synthesis.