Silicon hydrogensulfates: solid acids with exceptional 25 °C conductivities and possible electrochemical device applications?

Journal of Materials Chemistry A Pub Date: 2017-05-17 DOI: 10.1039/C6TA10956J

Abstract

Solid acids as a class are of much interest in areas such as acid catalysis, and exotic protonation chemistries. They include the strongest acids yet identified. A subclass exhibits very high protonic conductivity and its members have been investigated as possible fuel cell electrolytes, as first demonstrated by Haile's group in 2001 with CsHSO4. These superprotonic plastic crystals bring a “true solid state” alternative to polymer electrolytes, operating at mild temperatures (150–200 °C) without the requirement of humidification. However, they suffer from the narrow operating temperature range, and other problems. Here we describe a new class of solid acids based on silicon, which are of general interest. Its members have extraordinary conductivities, as high as 21.5 mS cm?1 at room temperature, orders of magnitude above any previous reported case. We discuss possible applications. Although the present electrolytes are not suitable for H2/O2 fuel cell applications due to hydrolizable components, a proof of principle short term fuel cell test is shown to produce a maximum (short circuit) current of 640 mA cm?2 at 87 °C despite a low open circuit voltage.

Graphical abstract: Silicon hydrogensulfates: solid acids with exceptional 25?°C conductivities and possible electrochemical device applications
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