Switching of photocurrent polarity in electrochemical cells with light via an excited state proton transfer mechanism

Light is the most targeted source of energy for sustainable energy technologies such as in photocurrent generation. While practically all light-harvesting types of applications utilize the electrons in their excited state (ES), here, we introduce a new conceptual approach that is based on ES proton transfer (ESPT). We use Brønsted photoacids and photobases that can donate or accept a proton, respectively, but only in their ES. Here, we use these molecules solvated in a photoelectrochemical single cell and explore the role of ESPT in photocurrent generation. We show at different bias regimes that the formed ions following the ESPT process can serve as electron donors or acceptors to the electrodes, which is dependent on the system and the presence of a photoacid or a photobase, resulting in modulating the photocurrent generation toward positive or negative currents. We further use an H-cell configuration that allows us to control the current polarity by switching the illumination between the cell containing the photoacid to the one containing the photobase. Our study represents a new approach in photoelectrochemistry by introducing ESPT processes, which can be further utilized in future devices targeting light-responsive energy production, energy storage, and hydrogen formation applications.