UC Irvine

Photoelectrochemical cells that utilize bipolar ion-exchange membranes (BPMs) can support and maintain a pH difference across the membrane. Redox-inactive salts are often also incorporated in these cells and it is unclear if salts have an effect on the electrostatics within the cell and perceived thermodynamics of the overall redox chemistry. In this thesis, commercial BPMs wetted by various electrolytes were investigated, e.g. in the presence of acid, base, and/or salt. The electrochemical behavior of the BPMs was assessed by measuring the current density vs potential behavior. The results suggest that potential differences measured across BPMs may not always reflect the pH of the bulk electrolyte and therefore may require additional information in order to justify the overall free energy required for the redox reactions.

The second half of this thesis was dedicated to the development of an artificial light-driven ion pump using BPM materials. An activated Nafion precursor membrane was functionalized with newly developed photoacid molecules and sandwiched between an anion-exchange membrane and a cation-exchange membrane. The photoelectrochemical properties of the resulting photoacid-functionalized BPM were measured and a photovoltaic response was observed. These initial findings provide a solid foundation for future research into customized BPMs to be used as artificial light-driven ion pumps.