Proton Environment Optimization Enhanced Asymmetric C1-C2 Intermediate Coupling for CO2 Reduction to n-Propanol.

The electrochemical conversion of CO2 into value-added n-propanol (n-PrOH) product is pivotal for establishing a sustainable carbon cycle. However, the process is severely hindered by the kinetically sluggish and uncontrolled asymmetric C1-C2 coupling step. Here, we develop a proton modulation strategy to optimize the CO2-to-C3 pathway. Structural engineering of the gas diffusion electrode modulates the H2O network environment at the triphasic interface, establishing a gradient H+ concentration environment that avoids the direct hydrogenation of *C2 intermediates. The Faradaic efficiency (FE) for n-PrOH reaches 21% at a partial current density of 167.5 mA cm-2 in a flow cell. In the membrane electrode assembly, the FEn-PrOH remains 19% at a partial current density of 132.9 mA cm-2. Mechanistic investigations identify *OCH2CH3 as the pivotal intermediate in n-PrOH formation. The simultaneous reduction of the formation energy barriers for both the C1-C1 and C1-C2 coupling rate-determining steps drives C3 product formation. This work highlights the significant role of proton environment engineering as a crucial parameter in the selection of the C3 product pathway.