Photoelectrochemical Ion Pumping with Dye-Functionalized Polymer Membranes

Artificial photosynthesis could be a cost-effective and sustainable means of converting sunlight energy into usable energy. Most artificial photosynthetic systems mimic nature’s properties of light absorption, electronic charge separation, and electronic charge collection, where ultimately electrons make and break chemical bonds. However, nature also transduces photon energy into proton gradients whose electric potential also drives chemical-bond formation. In my presentation I will report on my research group’s progress toward mimicking nature in function, by using light to drive endergonic proton transfer, ultimately converting photon energy into ionic current. The applicability and practicality of this material as a membrane in solar fuels devices and as a separate ionic photoelectrochemical device will also be discussed.

My research group’s near-term goal is to provide a proof-of-concept demonstration of an artificial proton pump where light-driven ion transport results in photovoltaic action. For an initial model system we utilized a conical nanopore etched in a polyethylene terephthalate plastic sheet. This pore was formed via swift heavy ion bombardment followed by alkaline chemical etching which resulted in a pore lined with fixed anionic functional groups. Then, using peptide coupling chemistries, the pore was asymmetrically functionalized with novel photoacids to generate a region containing fixed cationic dyes. This ordered distribution of interfacial charge was intended to mimic a solid-state semiconductor pn-junction and be used to separate photogenerated charges. We demonstrated that under visible-light illumination and a small reverse bias, excitation of the photoacid molecules resulted in an ionic photocurrent. We are currently expanding this initial research and successful demonstration of an artificial light-driven ion pump to other polymeric materials with hopes of generating ionic power through sunlight absorption and incorporating these materials as ion-exchange membranes in solar fuels devices.