Promoting CO2 Electroreduction to Multi-Carbon Products by Hydrophobicity-Induced Electro-Kinetic Retardation

Advancing the performance of the Cu-catalyzed electrochemical CO(2)reduction reaction (CO2RR) is crucial for its practical applications. Still, the wettable pristine Cu surface often suffers from low exposure to CO2, reducing the Faradaic efficiencies (FEs) and current densities for multi-carbon (C2+) products. Recent studies have proposed that increasing surface availability for CO(2)by cation-exchange ionomers can enhance the C(2+)product formation rates. However, due to the rapid formation and consumption of *CO, such promotion in reaction kinetics can shorten the residence of *CO whose adsorption determines C(2+)selectivity, and thus the resulting C2+FEs remain low. Herein, we discover that the electro-kinetic retardation caused by the strong hydrophobicity of quaternary ammonium group-functionalized polynorbornene ionomers can greatly prolong the *CO residence on Cu. This unconventional electro-kinetic effect is demonstrated by the increased Tafel slopes and the decreased sensitivity of *CO coverage change to potentials. As a result, the strongly hydrophobic Cu electrodes exhibit C(2+)Faradaic efficiencies of approximate to 90?% at a partial current density of 223 mA cm(-2), more than twice of bare or hydrophilic Cu surfaces.

Automated summary

Increasing the surface availability for CO(2) by using cation-exchange ionomers can enhance the C(2+) product formation rates in Cu-catalyzed electrochemical CO(2) reduction reaction (CO2RR). However, it also shortens the residence of *CO, leading to lower C(2+) selectivity. This study discovers that using quaternary ammonium group-functionalized hydrophobic polynorbornene ionomers can prolong the *CO residence time on Cu, resulting in significantly improved C(2+) Faradaic efficiencies.