Issue 20, 2018

Enhanced alkaline stability in a hafnium-substituted NaSICON ion conductor


We present here a multi-length scale integration of compositionally tailored NaSICON-based Na+ conductors to create a high Na+ conductivity system resistant to chemical attack in strongly alkaline aqueous environments. Using the Pourbaix Atlas as a generalized guide to chemical stability, we identify NaHf2P3O12 (NHP) as a candidate NaSICON material for enhanced chemical stability at pH > 12, and demonstrate the stability of NHP powders under accelerated aging conditions of 80 °C and pH = 13–15 for a variety of alkali metal cations. To compensate for the relatively low ionic conductivity of NHP, we develop a new low temperature (775 °C) alkoxide-based solution deposition chemistry to apply dense NHP thin films onto both platinized silicon wafers and bulk, high Na+ conductivity Na3Zr2Si2PO12 (NZSP) pellets. These NHP films display Na+ conductivities of 1.35 × 10−5 S cm−1 at 200 °C and an activation energy of 0.53 eV, similar to literature reports for bulk NHP pellets. Under aggressive conditions of 10 M KOH at 80 °C, NHP thin films successfully served as an alkaline-resistant barrier, extending the lifetime of NZSP pellets from 4.26 to 36.0 h. This integration of compositionally distinct Na+ conductors across disparate length scales (nm, mm) and processing techniques (chemically-derived, traditional powder) represents a promising new avenue by which Na+ conducting systems may be utilized in alkaline environments previously thought incompatible with ceramic Na+ conductors.

Graphical abstract: Enhanced alkaline stability in a hafnium-substituted NaSICON ion conductor

Supplementary files

Article information

Article type
10 Nov 2017
25 Mar 2018
First published
14 May 2018
This article is Open Access
Creative Commons BY license

J. Mater. Chem. A, 2018,6, 9691-9698

Enhanced alkaline stability in a hafnium-substituted NaSICON ion conductor

L. J. Small, J. S. Wheeler, J. F. Ihlefeld, P. G. Clem and E. D. Spoerke, J. Mater. Chem. A, 2018, 6, 9691 DOI: 10.1039/C7TA09924J

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