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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 19: Energy Storage and Batteries II
CPP 19.8: Vortrag
Dienstag, 19. März 2024, 11:30–11:45, H 0111
Coexistence of Cationic and Anionic Phosphate Moieties in the Solid Acid Cs7(H4PO4)(H2PO4)8 — •Christian Dreßler1, Jonas Hänseroth2, and Daniel Sebastiani2 — 1Theoretical Solid State Physics, TU Ilmenau, Germany — 2Theoretical Chemistry, MLU Halle-Wittenberg, Germany
We have studied the proton distribution and proton mobility in the recently synthesized solid state proton conductor Cs7(H4PO4)(H2PO4)8 by ab initio molecular dynamics simulations.[1] In agreement with experimental observations [2], we can clearly distinguish in our simulations an unusual cationic H4PO4+ and an anionic H2PO4− form that coexist in this solid acid. This paradox situation is achieved by partial substitution of Cs+ by H4PO4+ in CsH2PO4. Thus, HnPO4 act simultaneously as both the positive and the negative ion of the salt. We analyze the dynamical protonation pattern within the unusual hydrogen bond network that is established between the ions. Our AIMD simulations show that a conventional assignment of protonation states of the phosphate groups is not meaningful. Instead, a better description of the protonation situation is achieved by a fractional assignment of the strongly hydrogen-bonded protons to both its nearest and next-nearest oxygen neighbors. Furthermore, we also discuss the effect of the insertion of the cation H4PO4+ on the proton mobility.
[1] Dreßler, Hänseroth, Sebastiani, J. Phys. Chem. Lett. 2023, 14, 32, 7249-7255; [2] Wang, Patel, Sanghvi, Hu, Haile, J. Am. Chem. Soc. 2020, 142, 47, 19992-20001.
Keywords: ab initio molecular dynamics; proton exchange membrane; proton conduction; fuel cell; density functional theory