Enhanced alkaline stability in a hafnium-substituted NaSICON ion conductor. Issue 20 (14th May 2018)

• Record Type: Journal Article
• Authors: Small, Leo J.; Wheeler, Jill S.; Ihlefeld, Jon F.; Clem, Paul G.; Spoerke, Erik D.
• Is Part Of: Journal of materials chemistry. Volume 6:Issue 20(2018)
• Page Start: 9691
• Page End: 9698
• Publication Date: 2018-05-14
• Subjects: Materials -- Research -- Periodicals; Chemistry, Analytic -- Periodicals; Environmental sciences -- Research -- Periodicals; 543.0284
• DOI: 10.1039/c7ta09924j
• Languages: English
• ISSNs: 2050-7488

Abstract

Abstract : Substitution of Hf 4+ into NaSICON ion conductor crystal structure imparts improved resistance to alkaline degradation in aqueous media. Abstract : 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 NaHf2 P3 O12 (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 Na3 Zr2 Si2 PO12 (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.