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MXene-based catalysts exhibit extraordinary advantages for many catalysis reactions, such as the hydrogen evolution and oxygen reduction reactions. However, MXenes exhibit inadequate catalytic activity for the electrochemical nitrogen reduction reaction (NRR) because they are typically terminated with inactive functional groups, F* and OH*, which mask the active metal sites for N 2 binding. Here we modified the surface termination of MXene (Ti 3 C 2 T x ) nanosheets to achieve high surface catalytic reactivity for the NRR by ironing out inactive F*/OH* terminals to expose more active sites and by introducing Fe to greatly reduce the surface work function. The optimally performing catalyst (MXene/TiFeO x -700) achieved excellent Faradaic efficiency of 25.44% and an NH 3 yield rate of 2.19 μg/cm 2 ·h (21.9 μg/mg cat ·h), outperforming all reported MXene-based NRR catalysts. Our work provides a feasible strategy for rationally improving the surface reactivity of MXene-based catalysts for efficient electrochemical conversion of N 2 to NH 3 .

Atomically precise understanding of componential influences is crucial for looking into the reaction mechanism and controlled synthesis of efficient electrocatalysts. Herein, by means of comprehensive experimental and theoretical studies, we carefully examine the effects of component dopants on the catalytic performance of graphitic C 3 N 4 (g-C 3 N 4 )-based electrocatalysts. The g-C 3 N 4 monoliths with three types of dopant elements (B, P, and S) embedded in different sites (either C or N) of the C-N skeleton are rationally designed and synthesized. The kinetics, intrinsic activity, charge-transfer process, and intermediate adsorption/desorption free energy of the selected catalysts in oxygen reduction reaction and hydrogen evolution reaction are investigated both experimentally and theoretically. We demonstrate that the component aspect within the g-C 3 N 4 motifs has distinct and substantial effects on the corresponding electroactivities, and proper component element engineering can be a viable yet efficient protocol to render the metal-free composites as competent catalysts rivaling the metallic counterparts. We hope that this study may shed light on the empirical trial-and-error exploration in design and development of g-C 3 N 4 -based materials as well as other metal-free catalysts for energy-related electrocatalytic reactions.