Revisiting Electrocatalytic CO₂ Reduction in Nonaqueous Media: Promoting CO₂ Recycling in Organic Molecules by Controlling H₂ Evolution

Abstract

Electrochemical CO2 reduction to fuels or commodity chemicals using renewable energy has drawn attention as a strategy for closing the anthropogenic chemical carbon cycle. More than that, enhancing the C–C coupling between the intermediates could lead to producing a range of high‐value multi‐carbon molecules. Although the research mainly focuses on the aqueous media for the electrochemical CO2 reduction reaction (eRRCO2), using nonaqueous electrolytes has the advantage of suppressing the hydrogen evolution reaction, controlling the proton‐assisted reduction reactions, and favoring the C–C coupling. Herein, the use of nonaqueous electrolytes for eRRCO2 and the components of the electrochemical reactor that affect the selectivity of the reaction are revisited. This review provides a perspective view of recent findings compared to well‐established papers while presenting what is known about eRRCO2 in nonaqueous media.

K+ selectivity modulation in non-aqueous CO2 electroreduction on lead catalysts: from oxalic to tartaric acid production

“…The CO 2 reduction products in non-aqueous media have a considerably simple mechanism, as revised in ref. 15, 16 and 18, and can be identified using the FTIR spectrum combined with an analytical separation method, such as HPLC. Fig.…”

“…15–19 In the CO 2 RR, aprotic solvents can give more complex C 2+ molecules as products (oxalic acid, glycolic acid, and glyoxylic acid), leading to new CO 2 -based polymers. 20 Among the few electrocatalysts reported in the literature, lead-based electrodes are the most efficient catalyst to convert CO 2 into C 2+ products with higher faradaic efficiency, 15,16,21–28 but their selectivity relies mainly on the electrolyte solvent 19,22,29 and proton availability. 22,30–32…”

CO2 Electrolyzers

“…154−156 Organic solvents, despite their enhanced CO 2 solubility compared to aqueous electrolytes, pose challenges for cost-effective recycling in CO 2 reduction processes due to their high cost, volatility, flammability, toxicity, and potential mixing with desired products in the electrolyzer liquid. 156 Second, CO 2 R reactions and pathways are highly sensitive to the local microenvironment and thus the energetics of the reactions occurring on a catalyst's surface. 2,4 As the local microenvironment significantly changes with the current density and applied voltage, the results obtained with H-cells are not fully transferable to industrially relevant conditions.…”

“…First, the low solubility of CO 2 in aqueous electrolytes (34 mM at ambient conditions) results in mass transport limitations and, therefore, a low current density for CO 2 R. Numerous studies have explored nonaqueous electrolytes such as dimethyl sulfoxide (DMSO), acetonitrile, or propylene carbonate to address this issue. Some nonaqueous solvents have up to eight times greater CO 2 solubility than water, addressing mass transport limitations for achieving industrial-level current densities (>100 mA/cm 2 ) due to slow CO 2 diffusion in aqueous systems. − Organic solvents, despite their enhanced CO 2 solubility compared to aqueous electrolytes, pose challenges for cost-effective recycling in CO 2 reduction processes due to their high cost, volatility, flammability, toxicity, and potential mixing with desired products in the electrolyzer liquid . Second, CO 2 R reactions and pathways are highly sensitive to the local microenvironment and thus the energetics of the reactions occurring on a catalyst’s surface. , As the local microenvironment significantly changes with the current density and applied voltage, the results obtained with H-cells are not fully transferable to industrially relevant conditions.…”

Bryophyte-Bioinspired Nanoporous AAO/C/MgO Composite for Enhanced CO2 Capture: The Role of MgO

“…Alongside transitioning from fossil fuels to renewable energies like hydrogen, carbon recycling-utilizing CO 2 as a resource-emerges as a viable strategy for achieving a carbonneutral society [1]. Fujishima et al introduced a method involving hydrogen extraction through water electrolysis using electricity from high-efficiency solar cells [2] (methodology currently used and highly studied [3]), followed by combining this hydrogen with CO 2 emitted by power plants and factories to produce methanol, a potential energy source [4].…”