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. Instead, we are motivated by nature’s ability to transduce photon energy into proton gradients whose electrochemical potential also drives chemical-bond formation. In my presentation I will report on my research group’s recent success in demonstrating ionic power generation through solar light harvesting. Visible light was used to drive endergonic excited-state proton transfer from a photoacid-functionalized Nafion membrane. Photoacid molecules convert the energy in light into a change in the chemical potential of protons via a weakening of protic functional groups on the photoacid, i.e. a drop in its pKa. 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. Specifically, we characterized several bipolar membranes to more clearly understand their electrochemical behavior under conditions relevant to solar fuels devices. We identified a condition where the energy required to electrolyze water was seemingly less than 1.23 V, which we showed was due to transport of ions other than protons and hydroxide ions. Then, we covalently linked a new derivative of hydroxypyrene photoacid (pyranine) to Nafion sulfonyl fluoride precursor membranes and verified their binding spectroscopically. After sandwiching this membrane between an anion-exchange membrane and a cation-exchange membrane to form a three-layer bipolar membrane composite structure, we demonstrated photovoltaic action during visible-light excitation using four-electrode photoelectrochemical membrane-measurement techniques. As most of these materials and techniques are new to the solar fuels community, we plan to carefully present the results of our studies and provide ample explanation of the techniques. Collectively, this body of work represents several new directions in solar fuels research and development that are being pioneered by my research group.

Dye-sensitized bipolar ion-exchange membranes as artificial light-driven ions pumps for use in solar fuels devices

251st National Meeting (2016)

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