Optimized electron transfer in Ru/Cu@MXene electrocatalysts for ultra-selective and high-yield electrochemical NH3 synthesis

Electrocatalytic nitrogen oxide reduction (eNO x RR) has emerged as a promising alternative to the energy-intensive Haber-Bosch process for the sustainable production of ammonia (NH 3 ). However, challenges such as poor selectivity, multi-electron transfer pathways, and catalyst instability hinder industrial feasibility. To address these limitations, we report a Ru/Cu@MXene tandem electrocatalyst that strategically integrates Cu and Ru clusters on an MXene support to enhance NO x conversion efficiency. Prior to catalyst application in eNO x RR, we engineered the work function ( Φ ) of Ru-Cu-based clusters and attained an optimal Φ of 4.77 ​eV by incorporating Ru into the Cu@MXene, which facilitates efficient electron (e − ) flow from Ru to Cu. Specifically, Cu promotes strong NO adsorption, while Ru enhances e − transfer to the Cu–NO complex, creating a favorable reaction environment for selectivity of NO x to NH 3 . The synergistic Ru-to-Cu e − transfer mechanism was validated using ultraviolet photoelectron spectroscopy (UPS) and electrochemical analysis, confirming enhanced charge relocation. This optimized interface enabled Ru/Cu@MXene to achieve a high NH 3 yield of 338.35 ​μg ​cm −2 ​h −1 with NH 3 Faradaic efficiency (FE) of 86.77% and overall system's FE is 98.27% at −0.4 ​V, while simultaneously suppressing parasitic hydrogen (H 2 ) evolution. Theoretical calculations, including charge density difference (CDD), partial density of states (PDOS), and electrostatic potential mapping, further confirmed strong Ru/Cu interfacial coupling, which facilitates efficient NO adsorption and promotes a 5e − transfer pathway for NH 3 formation. Additionally, work function measurements (4.48 ​eV for Ru/Cu@MXene vs. 4.05 ​eV for Cu@MXene) demonstrated enhanced e − /H + mobility, further reinforcing the electrocatalyst's superior performance and stability. This study provides a novel tandem catalyst design that optimizes work function engineering for enhanced eNO x RR selectivity and efficiency, paving the way for scalable and sustainable electrochemical NH 3 production.