Eutectic CsHSO<sub>4</sub>-Coordination Polymer Glasses with Superprotonic Conductivity
Nattapol Ma, Nao Horike, Loris Lombardo, Soracha Kosasang, Kotoha Kageyama, Chonwarin Thanaphatkosol, Kanokwan Kongpatpanich, Ken‐ichi Otake, Satoshi Horike
Abstract
Superprotonic phase transition in CsHSO4 allows fast protonic conduction, but only at temperatures above the transition temperature of 141 °C (Tc). Here, we preserve the superprotonic conductivity of CsHSO4 by forming a binary CsHSO4-coordination polymer glass system, showing eutectic melting. Their anhydrous proton conductivities below Tc are at least 3 orders of magnitude higher than CsHSO4 without compromising conductivity at higher temperatures or the need for humidification, reaching 6.3 mS cm–1 at 180 °C. The glass also introduces processability to the conductor, as its viscosity below 103 Pa·s can be achieved at 65 °C. Solid-state NMR and X-ray pair distribution functions reveal the oxyanion exchanges and the origin of the preserved conductivity. Finally, we demonstrate the preparation of a micrometer-scale thin-film proton conductor showing low resistivity with high transparency (transmittance >85% between 380–800 nm).