First spectroscopic identification of pyrocarbonate for high CO2 flux membranes containing highly interconnected three dimensional ionic channels

Abstract

Identification of the existence of pyrocarbonate ion C₂O₅²⁻ in molten carbonates exposed to a CO₂ atmosphere provides key support for a newly established bi-ionic transport model that explains the mechanisms of high CO₂ permeation flux observed in mixed oxide-ion and carbonate-ion conducting (MOCC) membranes containing highly interconnected three dimensional ionic channels. Here we report the first Raman spectroscopic evidence of C₂O₅²⁻ as an active species involved in the CO₂-transport process of MOCC membranes exposed to a CO₂ atmosphere. The two new broad peaks centered at 1317 cm⁻¹ and 1582 cm⁻¹ are identified as the characteristic frequencies of the C₂O₅²⁻ species. The measured characteristic Raman frequencies of C₂O₅²⁻ are in excellent agreement with the DFT-model consisting of six overlapping individual theoretical bands calculated from Li₂C₂O₅ and Na₂C₂O₅.