Advanced solid acid electrolyte composites

Abstract

Solid acid/surface-hydrogen-containing secondary component electrolyte composites, methods of synthesizing such materials, electrochemical device incorporating such materials, and uses of such materials in fuel cells, membrane reactors and hydrogen separations are provided. The stable electrolyte composite material comprises a solid acid component capable of undergoing rotational disorder of oxyanion groups and capable of extended operation at a wide temperature range and a secondary compound with surface hydrogen atoms, which when intimately mixed, results in a composite material with improved conductivity, mechanical and thermal properties, when compared to pure solid acid compound.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS [0001] This application claims priority to U.S. Provisional Patent Application No. 60 / 699,018, filed Jul. 13, 2005, which is hereby incorporated by reference in its entirety for all purposes.STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT [0002] This work was support in part by a grant from the National Science Foundation, DMR-0413946. The government may have rights in certain aspects of this invention.BACKGROUND OF THE INVENTION [0003] Electrochemical devices depend on the flow of protons, or the flow of both protons and electrons, though a proton conducting material, such as a membrane. Accordingly, materials which conduct protons, or both protons and electrons, have applications as electrolytes or electrodes in a number of electrochemical devices including fuel cells, hydrogen pumps, supercapacitors, sensors, hydrogen separation membranes and membrane reactors. [0004] An important use for these m...

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Benefits of technology

[0011] The present invention is directed to a proton conducting membrane comprising a stable electrolyte composite material having high protonic conductivity, improved mechanical properties and capability of extended operation at a wide range of temperatures; methods of preparing such a proton conducting membrane; devices incorporating such a membrane; and uses of such a membrane in applications, such as fuel cells, hydrogen separations, membrane reactors and sensors. In particular, the proton conducting membrane comprises a stable electrolyte composite material comprising a solid acid component, a surface-hydrogen-containing secondary component and an interface formed between the solid acid component and the secondary component. The composite material has improved mechanical property. The secondary component can improve the mechanical stability of solid acid electrolyte membrane with respect to thermal creep by reducing the propensity of solid acids to plastically deform both at ambient and elevated temperatures. The interactions between the solid acid surface and the surface of the secondary compound can also stabilize the surface of the solid acid with respect to dehydration, thus allowing operation of the electrochemical device using the composite electrolyte to higher temperatures with respect to the same device using a solid acid compound alone as its electrolyte. Advantageously, the composite material can have one or more features or advantages, such as, for example, high conductivity from near ambient to elevated temperature; mechanically stabilizing with respect to thermal creep; kinetically stabilizing with respect to dehydration; and increased conductivity in its superprotonic phases.

Problems solved by technology

Regardless of the fuel cell design chosen, the operating efficiency of the device is partly limited by the efficiency of the electrolyte at transporting protons.

Accordingly, these materials must be hydrated, and a loss of water immediately results in degradation of the conductivity of the electrolyte and therefore the efficiency of the fuel cell.

Moreover, this degradation is irreversible, i.e., a simple reintroduction of water to the system does not restore the conductivity of the electrolyte.

These peripheral systems increase the complexity and cost of these fuel cells, from the use of expensive noble catalysts (Pt) to temperature requirements that cannot exceed much above 100° C. As a result of these temperature limitations, the fuel cell catalysts and other systems cannot be operated to maximum efficiency.

However, the lifetime of these sulfate and selenium based solid acids is short (Merle, R. B., et al.

Although the compound meets the necessary conditions of long term chemical stability for operation as a fuel cell electrolyte, the compound is water soluble and only becomes useful as an electrolyte above its superprotonic phase transition (Baranov, A. I., et al.

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