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We here report a mechanistic investigation into the electrochemical transport of CO2 through a dense metal-carbonate membrane. The investigation studied a total of six possible charge-transfer mechanisms involving CO32 CO22, O2-, CO24 and CO52 as the active surface species, and derived the corresponding flux equation from each mechanism. The experimental CO2 flux densities measured under a range of chemical gradients were used to verify each mechanism by plotting the flux density against the corresponding flux expression of each mechanism. The results showed that CO42 scheme is the best mechanism to describe the electrochemical CO2 transport through the metal-carbonate membranes. A new transport model was also shown to describe the CO42 migration and charge-transfer. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we systematically studied the effects of membrane thickness, CO2 concentration, and operating time on the CO2 flux density of an Al2O3-surface-modified and carbon-black-pore-former derived silver-carbonate membrane. It was found that the CO2 transport through a silver-carbonate membrane exhibited a critical thickness of 0.84mm, below which no flux enhancement could be achieved. The CO2 flux was also observed to be proportional to the difference of at the two reacting surfaces, and not the commonly assumed logarithmic partial pressure difference. The CO2 flux tested against time at 650°C increased by 200% for the first 160h, followed by a gradual decrease. At the 326-h marker, the flux was still the same as the original value when the test was started. Overall, the use of carbon black as a pore-former and Al2O3 as a surface modifier for silver-carbonate membranes has been proven effective and necessary to achieve a higher and more stable CO2 flux density. [Copyright &y& Elsevier]

Abstract: In this paper, we demonstrate that a silver-carbonate CO2 permeation membrane with the surface of silver matrix modified by a thin coating of Al2O3 can effectively improve the flux stability over an extended period. The CO2 and O2 flux densities reached 0.39mlcm−2 min−1 and 0.20mlcm−2 min−1 at 650°C, respectively, and maintained >90% of its original values for 130h. This is in contrast with the untreated membrane in which only one-third of the original values can be retained even after 60h. Overall, surface modification of silver matrix by a thin layer of Al2O3 coating is demonstrated as a viable method to fabricate stable silver-carbonate membranes for electrochemical CO2 capture from flue gas. [Copyright &y& Elsevier]

Abstract: One of the major concerns of consuming fossil fuels to produce useful form of energy is the emission of CO2, a greenhouse gas that can cause climate change and ultimately threaten the survival of humanity. Controlling CO2-emission is an urgent but only practical solution to stabilize CO2 concentration in the atmosphere. In this paper, we report our effort to capture CO2 from a simulated flue gas by utilizing a dual-phase mixed carbonate-ion and electron conducting membrane, namely molten carbonate and silver. The obtained CO2 and O2 flux densities are the highest among the published metal-molten carbonate systems and relatively stable over 80-h period. The measured CO2 and O2 flux densities not only exhibit similar activation energy but also have the ratio of 2:1, favorably confirming the surface electrochemical reaction of CO2 +1/2O2 +2e′=CO3 2−. These results demonstrate the Ag–MC dual-phase composite as a promising high-flux membrane for high-temperature electrochemical CO2 separation from flue gas with high selectivity. [Copyright &y& Elsevier]