6. Electrode Materials: State-of-the-Art and Experiments

Platinum is the most commonly used electrode material. The charge injection limit for platinum electrodes was found to be 400 μC∕cm² in [4]. Tim Boretius et al. have reported a value of only 75 μC∕cm² [3]. Platinum electrodes have proven success in practice, for example in many cochlear implants. Because of their relatively low charge injection capacity, they are usually used where large electrodes are applicable as in intracortical implant [8]. The limit for neural stimulation regarding tissue safety has been determined to be 1 mC∕cm². In order to increase the charge injection capacity of platinum, various approaches have been proposed in the past few decades, like the galvanization of platinum black or gray. Although platinum black possesses a highly porous layer and therefore high charge injection capacity, its deposition often requires a lead containing electrolyte which limits its application because of cytotoxicity concerns.