The Importance of Electrode Material in Bioelectronic Electrophoretic Ion Pumps

Bioelectronic ion pumps deliver ions and biomolecules from a source to a target biological system with high spatiotemporal control for bioengineering and regenerative medicine applications. A voltage between a working electrode and a reference/counter electrode delivers the charged ions and biomolecules from a source to the desired target. The source and the target are separated by an ion exchange membrane so that only the charged molecules of interest are delivered. Future wearable and implantable applications require high efficiency of delivery to minimize power consumption. The majority of recent efforts on improving ion pump efficiency have focused on optimizing the ion exchange membrane. However, the contribution of the working electrode material to the ion pump efficiency has been mostly overlooked. This work identifies how changing the working electrode material greatly affects the efficiency of delivery in ion pumps. With an electrical circuit model analysis, voltammetry studies on silver, platinum, and palladium hydride working electrodes, and implementation of the Butler–Volmer equation, results show that the material-dependent equilibrium potential at the working electrode surface has a large impact on ion pump efficiency. With this knowledge, a simple predictive model to optimize the working electrode material for delivering each specific ion or molecule of interest is designed.