Potential-dependent NRR/HER competition and N2 activation mechanism in M1M2@C6N6 bimetallic catalysts

Abstract

The performance decay of the electrochemical nitrogen reduction reaction (eNRR) at negative potentials is a primary obstacle to industrial implementation, which is predominantly attributed to the competition from the hydrogen evolution reaction (HER). In this work, a novel tiered screening strategy is proposed by integrating the computational hydrogen electrode (CHE) model and grand canonical ensemble constant-potential simulations to systematically investigate the potential-dependent competition of NRR and HER on M1M2@C₆N₆. Among 55 candidate catalysts, ScMn@C₆N₆ and VFe@C₆N₆ possessing high activity and selectivity are screened out, since they maintain a thermodynamic advantage for N₂ adsorption over a broad potential window. The equilibrium potential (U_eq) is defined as a critical benchmark to quantify the transition from N₂-dominant to H-dominant adsorption, which provides a rational explanation for the premature decline in NRR yield before reaching the mass transfer limit. Furthermore, a dual-pathway strategy is constructed to identify the decisive role of interatomic distance by interpretable Machine Learning (ML), and derive novel descriptors for understanding N₂ activation by symbolic regression. This research establishes a comprehensive theoretical framework and methodological guidance for rational design of highly selective electrocatalysts under realistic reaction conditions.