Ligands dependent electrocatalytic nitrogen reduction performance in d-π conjugated molecules

• A highly efficient molecular SAC has been found whose nitrogen reduction efficiency is comparable to other known SACs. • Most of the catalysts have extremely low NRR limiting potential and suppression of HER, among which CrCp and MnBz have extremely low limiting potentials of -0.29 V and -0.37 V, respectively. • In-depth research on the reaction mechanism found that the local magnetic moment plays a key role in the activation of nitrogen. • The descriptor of ΔE(*N 2 H) was discovered, and the mechanism was further investigated. The coordination environment of metal atoms in single-atom catalysts (SACs) has a greater impact on the catalytic performance of electrocatalysts. However, the influence mechanism of interacting ligands on the electrocatalytic nitrogen reduction reaction (NRR) process is still insufficient. Herein, by means of large-scale density functional theory (DFT) computations, the effect of organic ligands on the NRR process is investigated in-depth using half organometallic sandwich molecular SACs, i.e. TMBzs and TMCps (Bz = benzene, Cp = cyclopentadienyl, and TM = transition metal). The results revealed that the NRR performance of all the systems is highly dependent on the choice of d - π interaction within the TM-Ligand complexes. Compared with TMBzs, the TMCps exhibit outstanding NRR activity and significantly suppress HER. Among 16 candidates, CrCp and MnBz are the most promising candidates with an ultra-low limiting potential of -0.29 V and -0.37 V via consecutive mechanism, respectively. Moreover, the systems with higher spin polarizations have better NRR activity. The work provides new insight into the NRR to molecular SACs with different organic ligands.