Monolayers of choline chloride can enhance desired electrochemical reactions and inhibit undesirable ones

Electrocatalysis in deep eutectic solvents: from fundamental properties to applications

Electrocatalysis stands out as a promising avenue for synthesizing high-value products with minimal environmental footprint, aligning with the imperative for sustainable energy solutions. Deep eutectic solvents (DESs), renowned for their eco-friendly, safe, and cost-effective nature, present myriad advantages, including extensive opportunities for material innovation and utilization as reaction media in electrocatalysis. This review initiates with an exposition on the distinctive features of DESs, progressing to explore their applications as solvents in electrocatalyst synthesis and electrocatalysis. Additionally, it offers an insightful analysis of the challenges and prospects inherent in electrocatalysis within DESs. By delving into these aspects comprehensively, this review aims to furnish a nuanced understanding of DESs, thus broadening their horizons in the realm of electrocatalysis and facilitating their expanded application.

2D High-Entropy Transition Metal Dichalcogenides for Carbon Dioxide Electrocatalysis

High-entropy alloys combine multiple principal elements at a near equal fraction to form vast compositional spaces to achieve outstanding functionalities that are absent in alloys with one or two principal elements. Here, the prediction, synthesis, and multiscale characterization of 2D high-entropy transition metal dichalcogenide (TMDC) alloys with four/five transition metals is reported. Of these, the electrochemical performance of a five-component alloy with the highest configurational entropy, (MoWVNbTa)S₂ , is investigated for CO₂ conversion to CO, revealing an excellent current density of 0.51 A cm^-2 and a turnover frequency of 58.3 s^-1 at ≈ -0.8 V versus reversible hydrogen electrode. First-principles calculations show that the superior CO₂ electroreduction is due to a multi-site catalysis wherein the atomic-scale disorder optimizes the rate-limiting step of CO desorption by facilitating isolated transition metal edge sites with weak CO binding. 2D high-entropy TMDC alloys provide a materials platform to design superior catalysts for many electrochemical systems.

A General and Facile Approach for the Electrochemical Reduction of Carbon Dioxide Inspired by Deep Eutectic Solvents

Deep eutectic solvents (DESs) were applied to the electrochemical CO₂ reduction reaction (CO₂ RR). Choline-based DESs represent a non-toxic and inexpensive alternative to room-temperature ionic liquids (RTILs) as additives to the system or as electrolyte. Following the study on choline-based DESs this approach was generalized and simple and organic-soluble systems were devised based on the combination of organic chloride salts with ethylene glycol (EG), allowing the chlorides to be readily used as cocatalysts in the CO₂ RR. This approach negates the need for anion exchange and, because the chloride salt is usually the least expensive one, substantially reduces the cost of the electrolyte and opens the way for high-throughput experimentation.

The effect of electrolyte composition on the electroreduction of CO2 to CO on Ag based gas diffusion electrodes

The electroreduction of CO2 to C1-C2 chemicals can be a potential strategy for utilizing CO2 as a carbon feedstock. In this work, we investigate the effect of electrolytes on the electroreduction of CO2 to CO on Ag based gas diffusion electrodes. Electrolyte concentration was found to play a major role in the process for the electrolytes (KOH, KCl, and KHCO3) studied here. Several fold improvements in partial current densities of CO (jCO) were observed on moving from 0.5 M to 3.0 M electrolyte solution independent of the nature of the anion. jCO values as high as 440 mA cm(-2) with an energy efficiency (EE) of ≈ 42% and 230 mA cm(-2) with EE ≈ 54% were observed when using 3.0 M KOH. Electrochemical impedance spectroscopy showed that both the charge transfer resistance (Rct) and the cell resistance (Rcell) decreased on moving from a 0.5 M to a 3.0 M KOH electrolyte. Anions were found to play an important role with respect to reducing the onset potential of CO in the order OH(-) (-0.13 V vs. RHE) < HCO3(-) (-0.46 V vs. RHE) < Cl(-) (-0.60 V vs. RHE). A decrease in Rct upon increasing electrolyte concentration and the effect of anions on the cathode can be explained by an interplay of different interactions in the electrical double layer that can either stabilize or destabilize the rate limiting CO2˙(-) radical. EMIM based ionic liquids and 1 : 2 choline Cl urea based deep eutectic solvents (DESs) have been used for CO2 capture but exhibit low conductivity. Here, we investigate if the addition of KCl to such solutions can improve conductivity and hence jCO. Electrolytes containing KCl in combination with EMIM Cl, choline Cl, or DESs showed a two to three fold improvement in jCO in comparison to those without KCl. Using such mixtures can be a strategy for integrating the process of CO2 capture with CO2 conversion.

A Gross-Margin Model for Defining Technoeconomic Benchmarks in the Electroreduction of CO2

We introduce a gross-margin model to evaluate the technoeconomic feasibility of producing different C1 -C2 chemicals such as carbon monoxide, formic acid, methanol, methane, ethanol, and ethylene through the electroreduction of CO2 . Key performance benchmarks including the maximum operating cell potential (Vmax ), minimum operating current density (jmin ), Faradaic efficiency (FE), and catalyst durability (tcatdur ) are derived. The Vmax values obtained for the different chemicals indicate that CO and HCOOH are the most economically viable products. Selectivity requirements suggest that the coproduction of an economically less feasible chemical (CH3 OH, CH4 , C2 H5 OH, C2 H4 ) with a more feasible chemical (CO, HCOOH) can be a strategy to offset the Vmax requirements for individual products. Other performance requirements such as jmin and tcatdur are also derived, and the feasibility of alternative process designs and operating conditions are evaluated.