Active Hydrogen Dynamic Balance Strategy Improves Electrocatalytic Acetylene Semi-hydrogenation over Cu Nanoparticles/N-MXene.

Electrocatalytic acetylene semi-hydrogenation (EASH) is a green and sustainable route for converting acetylene to ethylene using water and renewable electricity under ambient conditions. In this work, Cu nanoparticles-anchored nitrogen-doped MXene catalyst (Cu NPs/N-MXene) was designed to construct electron-rich Cu active centers through interfacial electronic modulation of Cu sites by the two-dimensional conductive N-MXene framework. Benefiting from this electron-enriched Cu NPs/N-MXene interface, the catalyst effectively overcomes the conventional challenges of active hydrogen (*H) supply-demand imbalance and competitive HER during the EASH process at high current densities. In a gas-diffusion electrode flow cell, it maintains high activity in the range of 0.1-0.6 A cm-2, achieving a Faradaic efficiency for ethylene as high as 92.7% and an ethylene selectivity exceeding 98% at a high current density of 0.6 A cm-2. Additional DFT calculations reveal that the N-MXene-regulated interface lowers the barriers for water dissociation and the first acetylene hydrogenation step from 0.541 to 0.414 eV and from 0.51 to 0.16 eV, respectively, while increasing the barrier for ethylene over-hydrogenation from 0.34 to 0.52 eV. These concerted changes support more effective kinetic coupling between *H generation and its selective consumption through acetylene semi-hydrogenation. Consequently, a kinetic balance of rapid generation-efficient transfer-precise consumption of *H plays a critical role in enhancing EASH performance. This study provides an interfacial electronic structure regulation strategy for the electrocatalytic conversion of acetylene to ethylene at high current densities.