Using reciprocal derivative chronopotentiometry as a technique to determine safe charge injection limits of electrodes used for neural stimulation

We used reciprocal derivative chronopotentiometry (RDC) with platinum electrodes of 50 μm diameter in 0.15 M phosphate buffered saline solution to identify the various elec- trochemical processes occurring at the electrode during biphasic current pulsing. RDC allowed to determine the limits of water hydrolysis based on the specific (dt/dE)−E data representation employed in this technique resulting in curves similar to the voltammetric i−E response. Current stimulation was performed by either varying the pulse amplitude or pulse width. We found that the limits for H2 and O2 evolution for constant-amplitude pulses lied at 0.51 mC/cm2 and 0.67 mC/cm2, respectively, while for constant-width pulses they occurred at slightly lower values of 0.49 mC/cm2 and 0.61 mC/cm2, respectively. We could also extract values for the anodic and cathodic overvoltages associated with gas evolution. The cathodic overvoltage for H2 evolution was 1.43 V for both constant-amplitude and constant-width pulses, while the anodic overpotentials for O2 evolution were 2.45 V in the first and 2.24 V in the latter case. These values are clearly larger than the gas evolution limits generally found with steady- state voltammetry.status: publishe