Intensified Electrocatalytic CO₂ Conversion in Pressure‐Tunable CO₂‐Expanded Electrolytes

Abstract

Multimolar CO2 concentrations are achieved in acetonitrile solutions containing supporting electrolyte at relatively mild CO2 pressures (<5 MPa) and ambient temperature. Such CO2‐rich, electrolyte‐containing solutions are termed as CO2‐eXpanded Electrolytes (CXEs) because significant volumetric expansion of the liquid phase accompanies CO2 dissolution. Cathodic polarization of a model polycrystalline gold electrode‐catalyst in CXE media enhances CO2 to CO conversion rates by up to an order of magnitude compared with those attainable at near‐ambient pressures, without loss of selectivity. The observed catalytic process intensification stems primarily from markedly increased CO2 availability. However, a non‐monotonic correlation between the dissolved CO2 concentration and catalytic activity is observed, with an optimum occurring at approximately 5 m CO2 concentration. At the highest applied CO2 pressures, catalysis is significantly attenuated despite higher CO2 concentrations and improved mass‐transport characteristics, attributed in part to increased solution resistance. These results reveal that pressure‐tunable CXE media can significantly intensify CO2 reduction rates over known electrocatalysts by alleviating substrate starvation, with CO2 pressure as a crucial variable for optimizing the efficiency of electrocatalytic CO2 conversion.

Organic Electrosynthesis in CO2-eXpanded Electrolytes: Enabling Selective Acetophenone Carboxylation to Atrolatic Acid

“…CO), revealing total faradaic efficiencies that are less than unity (Supporting Information Table S1). Interestingly, we also observed similar faradaic efficiencies for CO 2 reduction to CO in our previous work using the same reactor setup (74% on Au 13 and 70% with Re(CO) 3 (bpy)Cl 14 ). This was attributed to the use of a single compartment electrochemical cell, which may allow some reduced species formed at the working electrode to be potentially oxidized at the counter electrode (or vice versa) resulting in lower faradaic yields.…”

“…12−14 We refer to these as CO 2 -eXpanded electrolytes because the liquid-phase volume expands with increasing CO 2 pressure (from 1.4−5.5 MPa) due to the dissolution of CO 2 (Supporting Information, Figure S1). In previous work, we observed (1) an order-of-magnitude enhancement of the catalytic current for CO 2 reduction to CO on heterogeneous catalysts (polycrystalline gold and copper), 12,13 (2) a significant enhancement of the catalytic rate for homogeneous (Re(CO) 3 (bpy)Cl (bpy = 2,2 -bipyridyl)) catalysts, 14 In this work, we demonstrate that the favorable properties of CXEs enhance the rate and selectivity of high-carbon content products via electrochemical carboxylation reaction pathways. Electrochemical carboxylation is an alternative approach to produce high-carbon-content carboxylic acids via the electrochemical coupling of CO 2 with organic compounds.…”

Enhancing Molecular Electrocatalysis of CO2 Reduction with Pressure‐Tunable CO2‐Expanded Electrolytes

“…Our recent findings [19,20] showed that significant quantities of CO 2 can be readily dissolved in acetonitrile (MeCN)c ontaining the supporting electrolyte tetrabutylammonium hexafluorophosphate, forming CXEs at CO 2 pressures of up to approximately 5.5 MPa. For example, the liquid-phasev olume is nearly doubled at approximately5MPa as ar esulto fC O 2 dissolution ( Figure 1a).…”

“…[18] We recently reported the development of CO 2 -eXpanded Electrolytes (CXEs) as CO 2 -rich media for studies of electrochemistry and electrocatalysis. [19] These media leverage the mild criticalp roperties of CO 2 and are formed at modest pressures (1.5-5.5 MPa), engenderingd issolution of significant quantities of CO 2 (up to 15 m)i nto liquid acetonitrile-based electrolytes. Using this continuum of pressure-tunable media, we have reported observations of up to an order-of-magnitude enhancement in the CO 2 reduction rate by using aheterogeneous gold catalyst and modeled the pressure-dependent kinetics and mechanism of CO 2 reduction by both golda nd copper electrode catalysts in CXEs.…”

Alkaline Co(OH)2-Decorated 2D Monolayer Titanic Acid Nanosheets for Enhanced Photocatalytic Syngas Production from CO2

“…This can be ascribed to the fact that the presence of TEOA can trap photoinduced holes to prohibit the electron− hole recombination, while MeCN used as a solvent is beneficial for enhancing the CO 2 solubility in the system. 47 When CO 2 is replaced with N 2 , negligible CO product is detected, indicating that CO 2 is the essential resource of the CO product. Moreover, without Co(OH) 2 /H 2 Ti 6 O 13 , the reaction system only produces a very small amount of CO.…”