Fig. 1. (a) Top view of MmXnTx. (b) Screened M element and X element. (c) Schematic illustration of all the considered MXenes.

Fig. 2. Plot of the G value, which shows the formation trend of the *O as a function of an applied potential on the M2C (a), M3C2 (b), M4C3 (c), M2N (d), M3N2 (e) and M4N3 (f). (g) Color block map of ULO for the O-functional MXenes. The different colored squares represent different numerical intervals of ULO.

Fig. 3. (a) Screening results of O-functional MXenes for NRR based on their performance for N2 capture (unit: eV). (b) Screening results based on H and N2 adsorption energy, where catalysts in the colorful region are in the promising area of NRR selectivity.

Fig. 4. (a) Sketch map of three thermodynamically unfavorable protonation steps (GN2-NNH, GNH-NH2 and GNH2-NH3). (b) Screening results of 4 selected candidates and some similar structures from refs. for NRR processes using the free energy changes of those steps.

Fig. 5. (a) Sketch map of reaction pathway. (b) Gibbs energy profiles of NRR processes without applied potential along the possible pathways on Nb3C2Ox, respectively. (c) Bond lengths of the N-N and N-Nb (the closest Nb atom of the adsorbed NxHy species) along the dissociation path B. (d) Bader charge analysis for N atom and Nb3 moiety.

Fig. 6. (a) Relationship between the Gibbs free energy and EN, EO. (b) List of DFT-calculated and elemental features for Gx prediction. (c) Correlation map of 23 features and Gx values. Red and Blue colors, bigger balls and more conspicuous number correspond to strong and direct correlation. (d) Feature importance of Gx calculated through Pearson correlation coefficient (dot) and mutual information (bar).

Fig. 7. Comparison between LASSO predictions and DFT calculations for GN2-NNH (a), GNH-NH2 (b) and GNH2-NH3 (c). (d) Equations for Gx prediction based on LASSO analysis using combined descriptors.