Mechanistic insights into carbon dioxide utilization by superoxide ion generated electrochemically in ionic liquid electrolyte

Halilu, Ahmed and Hayyan, Maan and Aroua, Mohamed Kheireddine and Yusoff, Rozita and Hizaddin, Hanee F. (2021) Mechanistic insights into carbon dioxide utilization by superoxide ion generated electrochemically in ionic liquid electrolyte. Physical Chemistry Chemical Physics, 23 (2). pp. 1114-1126. ISSN 1463-9076, DOI

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Understanding the reaction mechanism that controls the one-electron electrochemical reduction of oxygen is essential for sustainable use of the superoxide ion (O-2(-)) during CO2 conversion. Here, stable generation of O-2(-) in butyltrimethylammonium bis(trifluoromethylsulfonyl)imide BMAmm(+)]TFSI-] ionic liquid (IL) was first detected at -0.823 V vs. Ag/AgCl using cyclic voltammetry (CV). The charge transfer coefficient associated with the process was similar to 0.503. It was determined that BMAmm(+)]TFSI-] is a task-specific IL with a large negative isovalue surface density accrued from the BMAmm(+)] cation with negatively charged C(sp(2)) and C(sp(3)). Consequently, BMAmm(+)]TFSI-] is less susceptible to the nucleophilic effect of O-2(-) because only 8.4% O-2(-) decay was recorded from 3 h long-term stability analysis. The CV analysis also detected that O-2(-) mediated CO2 conversion in BMAmm(+)]TFSI-] at -0.806 V vs. Ag/AgCl as seen by the disappearance of the oxidative faradaic current of O-2(-). Electrochemical impedance spectroscopy (EIS) detected the mechanism of O-2(-) generation and CO2 conversion in BMAmm(+)]TFSI-] for the first time. The EIS parameters in O-2 saturated BMAmm(+)]TFSI-] were different from those detected in O-2/CO2 saturated BMAmm(+)]TFSI-] or CO2 saturated BMAmm(+)]TFSI-]. This was rationalized to be due to the formation of a BMAmm(+)]TFSI-] film on the GC electrode, creating a 2.031 x 10(-9) mu F cm(-2) double-layer capacitance (C-DL). Therefore, during the O-2(-) generation and CO2 utilization in BMAmm(+)]TFSI-], the C-DL increased to 5.897 mu F cm(-2) and 7.763 mu F cm(-2), respectively. The CO2 in BMAmm(+)]TFSI-] was found to be highly unlikely to be electrochemically converted due to the high charge transfer resistance of 6.86 x 10(18) k omega. Subsequently, O-2(-) directly mediated the CO2 conversion through a nucleophilic addition reaction pathway. These results offer new and sustainable opportunities for utilizing CO2 by reactive oxygen species in ionic liquid media.

Item Type: Article
Funders: Newton Fund Institutional Links Project (IF013-2015), RU Grant (GPF058A)
Uncontrolled Keywords: Carbon dioxide utilization; Superoxide ion; Ionic liquid electrolyte
Subjects: Q Science > QC Physics
Q Science > QD Chemistry
T Technology > TP Chemical technology
Divisions: Faculty of Engineering > Department of Chemical Engineering
Depositing User: Ms Zaharah Ramly
Date Deposited: 06 Jul 2022 07:59
Last Modified: 06 Jul 2022 07:59

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