Specifically Adsorbed Anions Enhance CO₂ Electrochemical Reduction to CO over a Gallium Catalyst in Organic Electrolytes

Abstract

The effects of anions (ClO 4 − , Cl − , Br − , and I − ) on CO selectivity in organic electrolytes have been studied. A gallium electrode with a low CO faradic efficiency was chosen to reveal the anion effects on CO 2 conversion. We found that the CO 2 reduction in a tetrabutylammonium chloride (Bu 4 NCl) solution exhibited more than 2 times higher CO faradic efficiency than that in the commonly used tetrabutylammonium perchlorate (Bu 4 NClO 4 ) solution. Also, Tafel plot measurement results showed that the presence of Cl − promoted an electron-transfer process, thus enhancing the reaction rate of CO 2 reduction. X-ray photoelectron spectroscopy (XPS) results further revealed that the solvated Cl − form the Ga−Cl bonds on the Ga surface. Electrons could flow from the electrode to the adsorbed Cl − and then flow to the CO 2 , resulting in the restriction of CO 2 near the Ga electrode. In the reaction, CO 2 was converted to a CO 2•− radical by receiving an electron, which flowed from Cl − to CO 2 via the Cl − -C bond. The obtained CO 2•− further combined with CO 2 to form the adduct of (CO 2 ) 2•− . After the second electron reaction, (CO 2 ) 2•− was converted to CO.

CO2 Electroreduction in Organic Aprotic Solvents: A Mini Review

“…, in DMF-0.7 (∼111.4), and DMSO-1.4 (∼194) [50]. A similar pattern is observed at other catalytically active cathodes.…”

“…Depending on the nature of the cathode surface in organic aprotic solvents, the reduction of CO 2 with the formation of oxalate or CO is possible. us, according to scheme (Figure 5(a)) on copper [31], gold [32,49], and gallium electrodes [50], CO is formed, according to scheme (Figure 5(b)) on stainless steel [51,52] and lead [33,53] electrodes-oxalate with high values of Faradaic efficiency (Table 1). On the electrode based on MoO 2 [31], the parallel reduction is possible according to schemes (a) and (b) with the formation of two products.…”

Deciphering Electrolyte Selection for Electrochemical Reduction of Carbon Dioxide and Nitrogen to High‐Value‐Added Chemicals

“…Acetonitrile (AN), dimethlyformamine (DMF), dimethyl sulfoxide (DMSO) and propylene carbonate (PC) are the most commonly reported organic solvents used in CO 2 RR since they can meet the harsh requirements of large negative potential for the electroreduction of CO 2 . [131][132][133][134][135][136][137] Pan et al obtained a nearly 100% total yield of carbon-containing products in AN/bicarbonate electrolyte (containing 75 vol.% AN), which decreases the proton availability and promotes *CO coupling to generate C 2 and C 3 products, indicating that HER can be almost completely hampered under properly controlled conditions. [136] Chu et al investigated an altered mechanism for Cu catalyzed C 2 H 4 electrosynthesis in DMSO solvent with a phenol/phenoxide (PhOH/PhO − ) proton donor environment.…”

Theoretical Insights into the Effects of KOH Concentration and the Role of OH– in the Electrocatalytic Reduction of CO2 on Au

“…A direct relationship was observed between the size and the electronegativity of the halide and their electrocatalytic performance with the rate and FE CO increasing as I − > Br − > Cl − . Chen et al 102 examined the influence of ClO 4 − , Cl − , Br − and I − anions on the reduction of CO 2 to CO over Ga and showed via XPS analyses the formation of Ga-Cl bonds and through Tafel slope analyses that specifically adsorbed Cl − promoted electron transfer to enhance the rate of CO 2 reduction. In a different study, Chen and Lipkowski 103 discuss the adsorption and electrovalency of OH − on Au(111) surface using FTIR spectroscopy and chronocoulometry.…”