Curvature- and pH-governed kinetics of electrocatalytic NO reduction on rare-earth single-atom catalysts: a DFT and constant-potential study.

The electrocatalytic NO reduction reaction (ENOR) offers a sustainable route for NH3 synthesis, yet the rational design of high-performance catalysts remains challenging due to the complex interplay between catalyst geometry and reaction environment. Herein, we systematically investigate how surface curvature and pH jointly regulate the ENOR kinetics on a series of rare earth single-atom catalysts (RE-SACs) supported on N-doped carbon nanotubes (RE@(m, m)N6CNT) using density functional theory (DFT) and constant-potential method (CPM) calculations. We find that decreasing surface curvature induces tensile strain, which upshifts the d- and f-band centers of RE atoms, thereby modulating the adsorption energetics of key intermediates and altering the potential-determining step (PDS). Notably, for Nd@(m, m)N6CNT, the PDS shifts from *NHOH hydrogenation to *NH2O hydrogenation as the curvature decreases. Among the screened catalysts, Ce@(13, 13)N6CNT exhibits exceptional ENOR activity with a low limiting potential (-0.17 V) and effectively suppresses the competing hydrogen evolution reaction and N2O byproduct formation. Using the CPM, we further reveal that pH exerts a strong influence on the onset potential: for Ce@(13,13)N6CNT, the onset potential is 0.281 V vs. RHE at pH = 1, significantly higher than at pH = 13 (-0.083 V vs. RHE), demonstrating that acidic conditions kinetically favor the reaction. This work establishes a mechanistic framework linking curvature-induced electronic effects and pH-dependent kinetics, providing design principles for RE-SACs toward an efficient ENOR.