ScholarWorks@성균관대학교

초록

This study reports that an optimal charge density in ionomers enhances the formation of C<INF>2</INF> products in Cu-catalyzed electrochemical CO<INF>2</INF> reduction reaction (CO<INF>2</INF>RR), challenging the established view in water electrolysis that higher charge density improves performance. Systematic variation of ion-exchange capacity (IEC) shows that it governs interfacial microenvironments by balancing the density of charged groups, ionic conductivity, water uptake, and hydrophobicity. An intermediate IEC creates a microenvironment that suppresses the hydrogen evolution reaction (HER) and favors the C<INF>2</INF> formation, achieving a Faradaic efficiency (FE<INF>C<INF>2</INF></INF>) of 38.2% with moderately active Cu catalysts in a two-compartment cell. In situ vibrational spectroscopy and molecular dynamics simulations reveal the orientations and dynamics of interfacial water, CO<INF>2</INF>, and *CO intermediates, as well as the hydrogen bond (H-bond) network of water under applied potentials. The optimized ionomer induces interfacial water molecules so that their hydrogen atoms point away from the electrode, thereby strengthening H-bonds and suppressing HER. It simultaneously tilts CO<INF>2</INF> relative to the electrode and thus increases the population of linearly bound *CO intermediates that facilitate C-C coupling. Incorporating the optimized ionomer into a flow cell further delivers partial current densities for C<INF>2+</INF> products above -500 mA cm-2 with FE<INF>C<INF>2+</INF></INF> over 70%. These findings reveal an unexplored role of IEC in tuning interfacial microenvironments and provide design principles for ionomers that selectively promote C<INF>2+</INF> formation in CO<INF>2</INF>RR.

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