UC Irvine

The key advance that led to the digital revolution was the invention of the solid-state diode, due to its ability to effectively rectify electronic current. Analogous, water-based diodes were invented around the same time, yet their ability to rectify protonic current paled in comparison. A suitable platform to fabricate water-based diodes is the bipolar ion-exchange membrane, which serves as a scaffold for dopants that ionize when infiltrated with protonically semiconducting water. Herein, by fashioning bipolar membranes into membrane-electrode assemblies and characterizing them like fuel cells, we report high-quality protonic diodes that, when sensitized to visible light using photoacids, exhibit “reverse” photovoltaic action. These demonstrations will spur innovations in the fields of iontronics, neuromorphic computing, and brain-machine interfaces, among others.