Electrical Stimulation with Pt Electrodes: II-Estimation of Maximum Surface Redox (Theoretical Non-Gassing) Limits

The maximum, biphasically applied charge which can be injected without electrolyzing water has been determined for Pt electrodes in simulated cerebral spinal fluid at 37°C. Electrolysis of water would lead to gas bubble formation, which is thought to be harmful. The experimental method involved the use of electrical transients. With lead (anodic faist) electrodes, the theoretical non-gassing limit is 300 ±20 μC/real cm², independent of current density in the range of ±50 to ±450 mA/cm². For lag (cathodic first) electrodes, the theoretical non-gassing limit is 350 ±50 μC/real cm² over the same current density range. In both cases, only part of the additional charge beyond these limits results in water electrolysis. Microscopic observations of bubble formation indicate that these limits are conservative. These limits are sufficiently large for most purposes; they do not restrict the use of Pt electrodes in stimulation.