Intermediate-temperature proton conductivity of Li+/H+ ion-exchanged material (Li,H)3.5Zn0.25GeO4

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Abstract
For decades, many efforts have been devoted to develop proton conductors applicable to electrochemical devices at intermediate temperatures. However, promising materials which possess sufficient conductivity have not been realized yet. This study demonstrates the development of novel proton conductors operative at intermediate temperatures, especially 300-400 ºC, through the simple ion-exchange method. The Li+/H+ ion-exchange was conducted for Li14Zn(GeO4)4, one of the members of lithium super ionic conductors (LISICONs), in non-aqueous solutions. The chemical formula of the resultant sample was determined as Li3.13H0.37Zn0.25GeO4 from instrumental analyses. The electrical conductivity of this material was evaluated to be 87.0 mS cm‒1, 39.0 mS cm‒1, and 5.5 mS cm‒1 at 400 ºC, 300 ºC, and 200 ºC, respectively, in 10% H2O‒90% N2. Furthermore, the main charge carrier in this electrolyte was identified as proton from the H/D isotopic exchange study. These findings open up the possibility of realizing new electrochemical devices operative at 200-400 °C.
Funding Information
  • New Energy and Industrial Technology Development Organization
  • Japan Society for the Promotion of Science (Grant-in-Aid for Scientific Research (B)/Grant No. JP20H02841)

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