Carbon dioxide transport in molten calcium carbonate occurs through an oxo-Grotthuss mechanism via a pyrocarbonate anion


The reactivity, speciation and solvation structure of CO2 in carbonate melts are relevant for both the fate of carbon in deep geological formations and for its electroreduction to CO (to be used as fuel) when solvated in a molten carbonate electrolyte. In particular, the high solubility of CO2 in carbonate melts has been tentatively attributed to the formation of the pyrocarbonate anion, C2O52–. Here we study, by first-principles molecular dynamics simulations, the behaviour of CO2 in molten calcium carbonate. We find that pyrocarbonate forms spontaneously and the identity of the CO2 molecule is quickly lost through O2– exchange. The transport of CO2 in this molten carbonate thus occurs in a fashion similar to the Grotthuss mechanism in water, and is three times faster than molecular diffusion. This shows that Grotthuss-like transport is more general than previously thought.

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Figure 1: Oxo-Grotthus mechanism via a pyrocarbonate anion.
Figure 2: Formation/dissociation of pyrocarbonate and C transport.
Figure 3: Geometry of pyrocarbonate anion.
Figure 4: Solvation structure around the CO2 molecule.
Figure 5: Solvation structure around the pyrocarbonate ion.


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The authors thank M. Cassir, V. Lair, B. Guillot, F. Gaillard, V. Haigis and A. Boutin for discussions. The research reported herein was funded by PSL Research University (project COOCAR, grant ANR-10-IDEX-0001-02) and Agence Nationale de la Recherche (project ELECTROLITH, grant ANR-2010-BLAN-621-03). This work was performed using HPC resources from GENCI (grants 2013-082309, 2014-082309 and 2015-082309) and IDRIS (grant ‘Grand Challenge’ 100577). The authors acknowledge PRACE for awarding access to Resource Curie, based in France at CEA Bruyères-le-Chatel (preparatory access allocation 2010PA2746).

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R.V. performed the FPMD simulations. D.C. analysed the trajectories, prepared the figures and wrote the manuscript. All authors designed the research, discussed the results and revised the manuscript.

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Correspondence to François-Xavier Coudert or Rodolphe Vuilleumier.

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The authors declare no competing financial interests.

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Corradini, D., Coudert, F. & Vuilleumier, R. Carbon dioxide transport in molten calcium carbonate occurs through an oxo-Grotthuss mechanism via a pyrocarbonate anion. Nature Chem 8, 454–460 (2016).

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