Transition Metal-Embedded C ₄ N ₄ Octahedral Rings as Highly Efficient Electrocatalysts for NO to NH ₃ Conversion: A Computational Study

The increasing pollution of nitric oxide (NO) along with the growing demand for ammonia (NH₃) has brought the electrochemical NO reduction reaction (NORR) toward NH₃ into the spotlight in the field of pollution control and green synthesis. In this study, 24 transition metal (TM) monatomic catalysts (TM-C₄N₄, TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Rh, Pd, Ag, Hf, Ta, W, Re, Os, Ir, Pt, Au) are systematically characterized by high-throughput first-principles calculations to assess their potential to convert NO to NH₃. Based on a five-step screening strategy, Cr-C₄N₄ is identified as the most promising catalytic system in terms of key indicators of adsorption strength, reaction barrier, and product selectivity. Cr-C₄N₄ not only has the lowest limiting potential (<i>U</i>_L = -0.10 eV) but also reveals excellent thermodynamic stability and high selectivity for the generation of NH₃. The intrinsic correlation between the key physicochemical descriptors and Δ<i>G</i>_*NO is demonstrated by combining machine learning and the SISSO algorithm. This work provides theoretical guidance for the efficient design of C₄N₄-supported single-atom catalysts in electrochemical NO to NH₃ conversion.