Enhanced Electrocatalytic CO₂ Reduction to C₂₊ Products by Adjusting the Local Reaction Environment with Polymer Binders

Abstract

sequestrated. Recently, electrochemical CO 2 reduction reactions (CO 2 RR) enabled by renewable energy have been suggested as a promising strategy to solve these problems, sequestrating discharged CO 2 into chemical feedstocks, and downscaling the use of fossil fuels in the chemical production industry. In addition, CO 2 RR is an efficient way to store electricity generated from intermittent renewable energies in the form of liquid fuels for transport and other applications. [3][4][5] Copper-based materials are the most investigated class of catalysts for CO 2 RR due to their unique ability to reduce CO 2 molecules to carbonaceous compounds containing more than two carbon atoms (C 2+ products). However, the high overpotential required and the low product selectivity over the pristine Cu surface have motivated researchers to develop more efficient strategies to overcome these challenges. Most previous publications have focused on engineering the properties of Cu-based catalysts, such as optimizing the size and shape of Cu nanomaterials, [6][7][8][9][10] introducing grain boundaries, [11] and creating alloys with other metals [12][13][14][15] to increase the number of active sites and/or to improve the intrinsic catalytic activities of Cu toward the desired products. Despite the tremendous progress that has been made, CO 2 RR is still not viable at an industrial scale.The activity and selectivity of the electrochemical CO 2 reduction reaction (CO 2 RR) are often hindered by the limited access of CO 2 to the catalyst surface and overtaken by the competing hydrogen evolution reaction. Herein, it is revealed that polymers used as catalyst binders can effectively modulate the accessibility of CO 2 relative to H 2 O at the vicinity of the catalyst and thus the performance of CO 2 RR. Three polymers with different hydrophilicities (i.e., polyacrylic acid (PAA), Nafion, and fluorinated ethylene propylene (FEP)) are selected as binders for Cu catalysts. At a thickness of only ≈1.2 nm, these binders strongly affect the activity and selectivity toward multi-carbon (C 2+ ) products. The FEP coated catalyst exhibits a C 2+ partial current density of over 600 mA cm −2 with ≈77% faradaic efficiency at −0.76 V versus RHE. This high performance is attributed to the hydrophobic (aerophilic) properties of FEP, which reduces the local concentration of H 2 O and enhances that of the reactant (i.e., CO 2 ) and the reaction intermediates (i.e., CO). These findings suggest that tuning the hydrophobicity of electrocatalysts with polymer binders can be a promising way to regulate the performance of electrochemical reactions involving gas-solid-liquid interfaces.

Zero-Gap Electrochemical CO2 Reduction Cells: Challenges and Operational Strategies for Prevention of Salt Precipitation

“…Much has been adopted from the already matured electrochemical hydrogen evolution reaction (HER) field, where performance metrics such as >1 A cm –2 conversion and >10,000 h lifetime are easily surpassed . By adopting technical features like the gas diffusion electrode (GDE) − and membrane electrode assembly (MEA) cell architecture, the field of CO 2 reduction has achieved industrially relevant current densities (>200 mA cm –2 ) while retaining selective conversion. These improvements were in part realized by utilizing highly alkaline electrolytes, such as KOH, to limit the competing HER ,− and humidifying the CO 2 gas stream to manage water availability to the cathode and membrane. , However, since being incorporated into more industrial reactors, additional challenges have been found which impact the long-term stability and economic feasibility of CO 2 RR.…”

Opening the pathway towards a scalable electrochemical semi-hydrogenation of alkynolsviaearth-abundant metal chalcogenides

“…In addition to the carbon support, the employed binder also plays a key role in tailoring the local environment around the catalytic particles. 37 Therefore, we altered the employed fluoropolymer binder from PTFE to PVDF as well as the added amount, to identify further tuning points. Overall, both PVDF and PTFE bound electrodes on SGL-GFD show FE values for the ECH of over 50%, with PTFE electrodes outcompeting their polymeric counterparts both in terms of activity for the ECH and specifically for the generation of MBE (Fig.…”

Polymer-Covered Copper Catalysts Alter the Reaction Pathway of the Electrochemical CO2 Reduction Reaction

“…Similarly, Luo et al employed fluorinated ethylene propylene (FEP) as a binder for the Cu catalyst to inhibit the competing HER reaction in aqueous CO 2 RR. 15 Nafion (with both hydrophilic and hydrophobic functional groups) and PAA (with hydrophilic functional groups) were also selected as binders to adjust the local environment of the Cu catalyst. The catalyst was prepared by dispersing both as-synthesized CuO particles and polymer in isopropyl alcohol and subsequent drop-casting on the electrode.…”

“…Electrolyte (light blue), Cu (brownish red), polymer binder (gray), CO 2 pathway (red arrow), H + pathway (blue arrow), and trapped CO 2 in hydrophobic samples (white). Reproduced with permission from ref ( 15 ). Copyright 2022 Wiley-VCH.…”