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

Abstract

Advancing the performance of the Cu‐catalyzed electrochemical CO2 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 CO2 by cation‐exchange ionomers can enhance the C2+ 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 C2+ 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 C2+ Faradaic efficiencies of ~90% at a partial current density of 223 mA cm‐2, more than twice of bare or hydrophilic Cu surfaces.

Dual Sites on Graphitic Biochar for Electrocatalytic CO2 Reduction to Ethanol Conversion

“…Moreover, the peaks around 875 cm –1 correspond to the C–C twisting vibration, and the peaks (≈1640 cm –1 ) over the P-CCDL-700 and Cu-CuO/P-CCDL-700 are attributed to the stretching vibration of CC from CC–CO (Figure S17, Supporting Information) . In addition, the double peaks around 1300–1400 cm –1 can be attributed to the C–O twisting vibration. , The same results of bonding of carbon were also confirmed by the Raman spectrum and the high-resolution C 1s spectrum.…”

“…27 In addition, the double peaks around 1300−1400 cm −1 can be attributed to the C−O twisting vibration. 16,27 The same results of bonding of carbon were also confirmed by the Raman spectrum and the high-resolution C 1s spectrum.…”

“…It is well-known that in the CO 2 RR process, the catalyst surface is wetted by the electrolyte, and the surface hydrophobicity of the catalyst is crucial for the construction of an efficient three-phase interface. 16 According to the wetting equation proposed by T. Young, the catalyst is hydrophobic when the contact angle is greater than 90°. Before the CO 2 RR, the contact angle of a water droplet on the Cu-CuO/P-CCDL-600 surface was 122.64°, slightly higher than that of Cu-CuO/P-CCDL-600 (120.56°) after the CO 2 RR (Figure 4d,e).…”

“…15 However, the surface hydrophobicity of the electrode surface is critical to the inhibition of hydrogen evolution reaction (HER). 16 Carbon materials are known for their hydrophobic nature. In addition, the selectivity for C 2+ products in CO 2 RR by Cu-based electrocatalysts has been extensively investigated.…”

“…Unfortunately, the competing proton reduction becomes kinetically advantageous in acidic solutions . However, the surface hydrophobicity of the electrode surface is critical to the inhibition of hydrogen evolution reaction (HER) . Carbon materials are known for their hydrophobic nature.…”