Effect of pH and gel electrolyte on safe charge injection and electrode degradation of platinum electrodes

Platinum (Pt) is a widespread electrode material choice for neural interfaces and electrochemical biosensors, due to its supposed electrochemical inertness. However, faradaic reactions can take place at Pt electrodes, including Pt oxide formation and reduction. Repeated redox cycles of Pt can lead to Pt dissolution, which may harm the tissue and significantly reduce electrode lifetime. In this study, we investigated how the electrolyte may influence Pt dissolution mechanisms during current pulsing. Two electrolyte characteristics were considered: pH and gelation. We confirmed that empirically reported tissue damage thresholds correlate with Pt oxide formation and reduction. Varying electrolyte pH occasioned a shift in recorded potentials, however, damage thresholds correlated with the same mechanisms for all pH values. The similar behaviour observed for pH values in the central range (4 ≤ pH ≤ 10) can be explained by variations of local pH at the electrode surface. Gel electrolytes behaved comparably to solutions, which was confirmed by statistical similarity tests. This study extends the knowledge about platinum electrochemistry and shows the necessity to carefully choose the stimulation protocol and the electrolyte to avoid platinum dissolution and tissue damage.