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.

We demonstrate the ability of tetraalkylammonium borohydrides to capture large amounts of CO2, even at low CO2 concentrations, and reduce it to formate under ambient conditions. These materials show CO2 absorption capacities up to 30 mmolCO2  g−1 at room temperature and 1 bar CO2. Every BH4− anion can react with three CO2 molecules to form triformatoborohydride ([HB(OCHO)3]−). The thermodynamics and kinetics of the reaction were monitored by a magnetic suspension balance (MSB). Direct CO2 capture and reduction from air was achieved with tetraethyl, ‐propyl, and ‐butylammonium borohydride. The alkyl chain length played an important role in the kinetics and thermodynamics of the reaction, especially in CO2 diffusivity (crystallinity and free‐volume), activation energy (charge‐transfer dependent on the alkyl chain), and hydrophobicity. Adding HCl gave formic acid and the corresponding chloride ammonium salt, which can be recycled. In addition, transfer of formate was achieved for the N‐formylation of an amine.

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