Electrochemical Devices Based on Solid Acid Electrolytes for Conversion of Methane Derivatives

A boom in natural gas production in the United States presents opportunities for economically effective use of methane-derived molecules.  In contrast with methane gas, derivatives may exhibit advantages in volumetric energy density, ease of transport and versatility.  Electrochemical conversion of these species to electricity and other fuels is desirable, but depending on the system in question, catalyst stability, activity, and impurity intolerance, or alternately, the cost and durability of the electrolyte may be impediments to adoption

The solid-state proton conductor cesium dihydrogen phosphate (CsH₂PO₄ or CDP) has shown potential in electrochemical devices operating on fuels such as reformed NG or methanol. CDP undergoes a solid-solid phase transition at 228 °C and an associated increase in proton conductivity of more than three orders of magnitude (8.5 x 10^-5 S cm^-1 at 223 °C to 2.5 x 10^-2 S cm^-1 at 250 °C).  These systems have been shown to tolerate reformate streams in H₂-air cells containing CO, H₂S, NH₃, CH₃OH, C₃H₈ and CH₄ of 20%, 100ppm, 100 ppm, 5%, 3% and 5% respectively, retaining 90-95% of pure H₂ performance¹. Solid acid fuel cells operated using methanol and an integrated steam reformer have also shown similar results².  Recently, we showed that this material can also be used in an electrochemical hydrogen separation system using similar reformate streams³. 

In the majority of these earlier studies, platinum was used as the catalyst for both the hydrogen reduction and oxidation reactions. We have also demonstrated that unsupported nickel is an effective hydrogen evolution catalyst in solid acid hydrogen pump devices⁴.  Here, we have synthesized a suite of carbon-supported non-platinum catalysts (Pt, Pd, Ru, Ni and Cu) for implementation in electrodes.  We evaluate these materials as hydrogen oxidation and evolution catalysts in CDP-based devices for electricity and fuel production from the methane derivatives methanol and dimethyl ether.

This work is supported by the National Science Foundation through TN-SCORE (EPS-1004083).

References

¹ C. R. I. Chisholm et al., Electrochem. Soc. Interface, 18, 53–59 (2009).

² T. Uda, D. a. Boysen, C. R. I. Chisholm, and S. M. Haile, Electrochem. Solid-State Lett., 9, A261 (2006).

³ A. B. Papandrew et al., J. Electrochem. Soc., 161, F679–F685 (2014).

⁴ A. B. Papandrew, T.A. Zawodzinski Jr., J. Power Sources 245 (2014) 171.