Bicarbonate Electroreduction to Multicarbon Products Enabled by Cu/Ag Bilayer Electrodes and Tailored Microenviroments

Abstract

Bicarbonate electrolyzer can achieve the direct conversion of CO2 capture solutions that bypasses energy‐intensive steps of CO2 regeneration and pressurization. However, only single‐carbon chemicals (i. e., CO, formate, CH4) were reported as the major products so far. Herein, bicarbonate conversion to multicarbon (C2+) products (i. e., acetate, ethylene, ethanol, propanol) was achieved on rationally designed Cu/Ag bilayer electrodes with bilayer cation‐ and anion‐conducting ionomers. The in‐situ generated CO2 was first reduced to CO on the Ag layer, followed by its favorable further reduction to C2+ products on the Cu layer, benefiting from the locally high concentration of CO. Through optimizing the bilayer configurations, metal compositions, ionomer types, and local hydrophobicity, a microenvironment was created (high local pH, low water content, etc.) to enhance bicarbonate‐to‐C2+ conversion and suppress the hydrogen evolution reaction. Subsequently, a maximum C2+ faradaic efficiency of 41.6±0.39 % was achieved at a considerable current density of 100 mA cm−2.

A minireview on electrochemical CO2 conversion based on carbonate/bicarbonate media

“…Further investigations revealed that the hydrophobic alkyl group of CTAB increased the local CO 2 concentration near the catalyst surface, thereby promoting CH 4 production. Lee et al 39 first reported a case for direct electrochemical conversion of HCO 3 − solution into C 2+ products by a Cu/Ag bilayer electrode. The C 2+ products mainly include C 2 H 4 , acetate, ethanol, and 1-propanol and the maximum FE of C 2+ reached 41.6% at a current density of 100 mA cm −2 and a cell voltage of 3.9 V.…”

Integration of CO2 Capture and Electrochemical Conversion

“…After that, several different cathode catalysts can be used in the same system to give rise to different products. For example, a Cu/Ag bilayer cathode delivered a 41.6% FE (C2+) at 100 mA cm –2 , while Ag/GDL and Ni SACs cathodes achieved 37% and 62% FE (CO) at 100 mA cm –2 , and a Bi/C cathode achieved 62% FE (HCOO−) at 100 mA cm –2 . ,, To further increase the FE of the CO 2 RR, some strategies to increase the catalyst’s local CO 2 concentration and CO 2 solubility have been employed, like using the cationic surfactant, decreasing the catalyst layer thickness, and increasing the operating pressure . For instance, Zhang et al found that several factors, such as the operation temperature, pressure, electrolyte flow rate, and flow channel shape, significantly influence product FE for electrochemically converting KHCO 3 to CO. By using a porous Ag cathode at 100 mA cm –2 , 78% and 95% of FE (CO) were obtained with an inlet electrolyte temperature of 70 °C at 1 atm and 20 °C at 4 atm, respectively, while only 59% of FE (CO) was achieved at 1 atm and 20 °C.…”

Recent Advances in Electrochemical CO2‐to‐Multicarbon Conversion: From Fundamentals to Industrialization

“…[ 201 ] While, Li and co‐workers adopted the direct multi‐step spraying process to obtain a self‐made GDEs with bimetal layers for cascade conversion. [ 271 ]…”