Synergistic double-atom catalysts of metal-boron anchored on g-C2N for electrochemical nitrogen reduction: Mechanistic insight and catalyst screening

Abstract

The rational design of a novel catalytic center with a sound basis remains both challenging and rewarding for the electrochemical reduction of N2 (eNRR), which has provided a feasible route for achieving clean and sustainable NH3 production under ambient conditions. Herein, using density functional theory calculations, we demonstrate that hybrid metal (M)-boron (B) double-atom catalysts (DACs) embedded in g-C2N substrate (M−B@C2N, M = 3d, 4d and 5d transition metals) can achieve both high catalytic activity and high selectivity in eNRR. The proposed M−B@C2N DACs have exhibited impressive feasibility and stability thanks to the resilient and robust C2N substrate with abundant pyridinic N atoms distributed among right-sized pore structures. Our results reveal that like the metal center, the embedded B atom can actively involve in NN bond activation via π*-backdonation mechanism concomitant with the substantial charge transfer to adsorbed *N2, leading to sizable NN bond elongation. Accordingly, both adsorption energy and NN bond length of *N2 can be employed as catalytic descriptors for predicting eNRR activity in terms of the limiting potentials (UL). Using high-throughput screening method, we found that six M−B@C2N candidates have stood out as the outstanding electrocatalysts for driving eNRR, namely, M = Ti (UL = 0 V), Mo (UL = 0 V), Nb (UL = -0.04 V), W (UL = -0.23 V), Zr (UL = -0.26 V), V (UL = -0.28 V). The underlying origin is attributed to the balanced and constrained N-affinity of M−B dual site working in synergy, which can thus be used as one important guide of catalyst design.