Kinetics and mechanism of electrochemical oxidation of carbon monoxide in molten carbonates. Confirmation of the existence of the CO2–2 ion
- 1 January 1977
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases
- Vol. 73, 1420-1435
- https://doi.org/10.1039/f19777301420
Abstract
The kinetics and mechanism of the electrochemical oxidation of CO in molten alkali carbonate electrolyte have been determined by analysis of steady-state polarization and potential-scan data on 99.99 % pure gold electrodes at 800°C. Results show that of the two oxidation processes occurring, the first is due to physically dissolved CO, whereas the second process, whose half-wave potential is + 240 to + 300 mV (std. CO/CO2) is due to CO combined chemically with the melt, the reacting species being the CO2– 2 ion. For a 0.382 atm CO + 0.618 atm CO2 mixture, the concentration of physically dissolved CO is estimated to be ∼2 × 10–4 mol dm–3. The concentration of CO2– 2 ion is ∼8 times higher. Good agreement has been found between the results obtained independently from steady-state, potential-scan, electrolyte additive and gas-solubility studies. Exchange current densities are ∼2.2 × 10–4 and 2.9 × 10–4 A cm–2 for 0.05 atm CO and 0.382 atm CO (at 0.618 atm CO2), of which ∼40 and 30 % respectively result from oxidation of the CO2– 2 ion. The sequence of the individual reaction steps has been identified for each of these processes. The rate-determining reaction in the first process is: CO++ CO2– 3→ CO– 2+ CO2. The second process shows that, depending on the CO/CO2 composition, the rate determining step is either: CO2– 2→ CO– 2+ e–, or that identified for the first process.Keywords
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