Hydrogen generation using novel hydrocarbon anion, cation, and bipolar membrane materials

The development of chemically stable and mechanically robust hydrocarbon ion exchange membranes is critical for the advancement of water electrolyzers. The acidic perfluorinated cation exchange membranes currently in use are expensive to manufacture, and pose significant environmental issues. Anion exchange membranes, which operate under basic conditions, are typically non-fluorinated, but lack stability in base and do not offer high ionic conductivities. In this thesis, novel hydrocarbon anion and cation exchange membranes were characterized electrochemically to better understand their properties and in-situ performance. In chapter 2, mono-pH systems are explored using a catalyst coated membrane placed in a water electrolysis cell. It was found that the hydrocarbon membranes used in this research can be successfully operated in water electrolysis cells, in particular hydrocarbon anion exchange membranes with enhanced stability in base. Hydrocarbon bipolar membranes, which consist of anion and cation exchange membrane layers, were explored in chapters 3 and 4 using a 4-electrode system. Using bipolar membranes allows for the anode and cathode reactions to occur at different pHs. In chapter 3, we showed the effects of utilizing a 3D junction at the bipolar membrane interface with and without a water dissociation catalyst. Chapter 4 illustrates how varying anion and cation exchange membrane thickness within a bipolar membrane effects performance, as measured by current-voltage curves and a novel spectroelectrochemical method. This data was then correlated with permselectivity measurements to show the relationship between permselectivity of a single bulk layer and co-ion leakage currents through the bipolar membrane. Through this work it was confirmed that bipolar membranes with high surface area junctions and water dissociation catalysts exhibit better performance. Additionally, it was shown that the thickness of individual CEM and AEM layer should be tailored to each polymer's permselectivity to maximize water dissociation efficiency. However, the bipolar membranes used in this research suffered from a lack of adhesion when using a water dissociation catalyst. Alternative methods for bipolar membrane fabrication should continue to be explored.