Unveiling the Underlying Mechanism of Transition Metal Atoms Anchored Square Tetracyanoquinodimethane Monolayers as Electrocatalysts for N Fixation

We for the first time systematically studied the structures and electrochemical nitrogen reduction reaction properties of two-dimensional single transition-metal anchored square tetracyanoquinodimethane monolayers（labeled as: TM-s TCNQ, TM = 3d, 4d, 5d series transition metals） by employing density functional theory method. Through highthroughput screenings and full reaction path researches, two promising electrochemical nitrogen reduction reaction catalysts Nb-s TCNQ and Mos TCNQ have been obtained. The nitrogen reduction reaction onset potential on Nb-s TCNQ is as low as-0.48 V. Furthermore, the Nb-s TCNQ catalyst can quickly desorb NH3produced with a free energy of 0.65 e V, giving Nb-s TCNQ excellent catalytic cycle performance. The high catalytic activity of the two materials might be attributed to the effective charge transfer between the active center and adsorbed N2, which enables the active center to adsorb and activate inert N2molecules well, and the reduction processes require small energy input（i.e., the maximum free energy changes are small）. This work provides insights for finding highly efficient, stable, and low-cost nitrogen reduction reaction electrocatalysts. We hope our results can promote further experimental and theoretical research of this field.