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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, H_nPO₄ 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