Revealing the Adsorption Behavior of Nitrogen Reduction Reaction on Strained Ti 2 CO 2 by a Spin-Polarized d-band Center Model.

Electrocatalytic reduction of dinitrogen to ammonia has attracted significant research interest. Herein, it reports the boosting performance of electrocatalytic nitrogen reduction on Ti 2 CO 2 MXene with an oxygen vacancy through biaxial tensile strain engineering. Specifically, tensile strain modified electronic structures and formation energy of oxygen vacancy are evaluated. The exposed Ti atoms with additional electron states near the Fermi level serve as active site for intermediate adsorption, leading to superior catalytic performance (U limit = -0.44 V) under 2.5% biaxial tensile strain through a distal mechanism. However, the two sides of the "Sabatier optimum" in volcano plot are not limited by two different electronic steps, but are induced by the diverse adsorption behaviors of intermediates. Crucially, the "Sabatier optimum" results from the different response speeds of the adsorption energy for *N 2 and *NNH to strains. Moreover, the authors observe conventional d-band adsorption for *N 2 and *NNH, non-linear adsorption for *NNH 2 , and abnormal d-band adsorption for *N, *NH, *NH 2 , and *NH 3 , which can be explained by the competition between attractive orbital hybridization and repulsive orbital orthogonalization with the spin-polarized d-band model, which further clarifies the contributions of 3σ → d z2 and d xz /d yz → 2π* to the overall population of bonding and anti-bonding states.