Chain-Length-Dependent Alkanethiol Modification of Porous Cu2O Cubes for Selective CO2 Electroreduction to Ethylene at High Current Densities.

The electrochemical reduction of CO2 to ethylene (C2H4) holds promise for sustainable fuel production, yet achieving high selectivity at industrial current densities remains challenging. Herein, we report a strategy that enables effective control over C2H4 selectivity even at high current densities by modifying hierarchically porous Cu2O cubes with alkanethiols. The low electrical conductivity of the alkanethiol induces electric field screening at the catalyst surface, which steers interfacial water into a strongly hydrogen-bonded network while promoting partial dehydration of K+ ions. Their synergistic effects not only suppress the competing hydrogen evolution reaction (HER) but also promote the hydrogenation of adsorbed CO* to form CHO*. This, in addition to conventional CO* dimerization, establishes an alternative pathway for C-C bond coupling via the CO*-CHO* route, thereby ensuring high C2H4 selectivity. Notably, this effect is further amplified as the alkanethiol chain length increases from C12 to C18. Consequently, the catalyst modified with the C18 alkanethiol achieves a Faradaic efficiency of 66.7% for C2H4 with a partial current density of 133.6 mA cm-2 at a total current density of 200 mA cm-2. This work highlights the importance of the interfacial microenvironment for C-C coupling toward multicarbon products at industrial current densities.