Facile Proton Transport in Ammonium Borosulfate—An Unhumidified Solid Acid Polyelectrolyte for Intermediate Temperatures
Abstract
High proton conductivity is reported for unhumidified ammonium borosulfate, NH4[B(SO4)2], a solid acid coordination polymer that contains 1D, hydrogen‐bonded NH4+···1∞[B(SO4)4/2]− chains. NH4[B(SO4)2] is thermally stable to 320 °C and is amenable to sintering into monolithic, polycrystalline discs at 200 °C and about 300 MPa of uniaxial pressure. Impedance spectroscopy measurements reveal ionic conductivities for sintered ammonium borosulfate of 0.1 mS cm−1 at 25 °C and up to 10 mS cm−1 at 180 °C in ambient air. No superprotonic transition is observed in the temperature range of 25–180 °C. Ab initio molecular dynamics simulations show these high conductivities are aided by free rotation of the NH4+ units and significant gyrational mobility of the SO4 tetrahedra, which, in turn, provide facile pathways for proton locomotion. High conductivities, a wide operational temperature window, and tolerance to both ambient and anhydrous conditions make NH4[B(SO4)]2 an attractive candidate electrolyte for intermediate‐temperature hydrogen fuel cells that may enable operation at temperatures as high as 300 °C without active humidification.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Sep 13, 2020
- Source ID
- 10.1002/adma.202003667
Entities
People
- Albert Epshteyn
- Brian L Chaloux
- Matthew D Ward
- Michelle D Johannes
Organizations
- Office of Naval Research
- United States Naval Research Laboratory