TY - JOUR
T1 - Structure and Properties of Cs7(H4PO4)(H2PO4)8
T2 - A New Superprotonic Solid Acid Featuring the Unusual Polycation (H4PO4)+
AU - Wang, Louis S.
AU - Patel, Sawankumar V.
AU - Sanghvi, Sheel S.
AU - Hu, Yan Yan
AU - Haile, Sossina M.
N1 - Funding Information:
Financial support has been provided by the National Science Foundation (DMR 1807234 and DGE-1842165). Single-crystal XRD experiments made use of the Integrated Molecular Structure Education and Research Center (IMSERC) at Northwestern University, which is supported by the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205, the State of Illinois, and International Institute for Nanotechnology (IIN)). We thank Charlotte Stern and Christos Malliakas for single-crystal data collection and discussion on structure refinement. This work made use of the J. B. Cohen X-ray Diffraction facility at NU, supported by the NSF MRSEC program (NSF DMR-1720139), and we thank Jerry Carsello for his years assisting our experiments as facility manager.
PY - 2020/11/25
Y1 - 2020/11/25
N2 - We report the discovery of a new superprotonic compound, Cs7(H4PO4)(H2PO4)8, or CPP, which forms at elevated temperatures from the reaction of CsH2PO4 and CsH5(PO4)2. The structure, solved using high-temperature single-crystal X-ray diffraction and confirmed by high-temperature 31P NMR spectroscopy, crystallizes in space group Pm3¯ n and has a lattice constant of 20.1994(9) Å at 130 °C. The unit cell resembles a 4 × 4 × 4 superstructure of superprotonic CsH2PO4, but features an extraordinary chemical moiety, rotationally disordered H4PO4+ cations, which periodically occupy one of every eight cation sites. The influence of this remarkable cation on the structure, thermodynamics, and proton transport properties of the CPP phase is discussed. Notably, CPP forms at a temperature of 90 °C, much lower than the superprotonic transition temperature of 228 °C of CsH2PO4, and the compound does not appear to have an ordered, low-temperature form. Under nominally dry conditions, the material is stable against dehydration to ∼151 °C, and this results in a particularly wide region of stability of a superprotonic material in the absence of active humidification. The conductivity of Cs7(H4PO4)(H2PO4)8 is moderate, 5.8 × 10-4 S cm-1 at 140 °C, but appears nevertheless facilitated by polyanion (H2PO4-) group reorientation.
AB - We report the discovery of a new superprotonic compound, Cs7(H4PO4)(H2PO4)8, or CPP, which forms at elevated temperatures from the reaction of CsH2PO4 and CsH5(PO4)2. The structure, solved using high-temperature single-crystal X-ray diffraction and confirmed by high-temperature 31P NMR spectroscopy, crystallizes in space group Pm3¯ n and has a lattice constant of 20.1994(9) Å at 130 °C. The unit cell resembles a 4 × 4 × 4 superstructure of superprotonic CsH2PO4, but features an extraordinary chemical moiety, rotationally disordered H4PO4+ cations, which periodically occupy one of every eight cation sites. The influence of this remarkable cation on the structure, thermodynamics, and proton transport properties of the CPP phase is discussed. Notably, CPP forms at a temperature of 90 °C, much lower than the superprotonic transition temperature of 228 °C of CsH2PO4, and the compound does not appear to have an ordered, low-temperature form. Under nominally dry conditions, the material is stable against dehydration to ∼151 °C, and this results in a particularly wide region of stability of a superprotonic material in the absence of active humidification. The conductivity of Cs7(H4PO4)(H2PO4)8 is moderate, 5.8 × 10-4 S cm-1 at 140 °C, but appears nevertheless facilitated by polyanion (H2PO4-) group reorientation.
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U2 - 10.1021/jacs.0c08870
DO - 10.1021/jacs.0c08870
M3 - Article
C2 - 33180477
AN - SCOPUS:85096889572
VL - 142
SP - 19992
EP - 20001
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 47
ER -