Objective. Neural stimulation is usually performed with fairly large platinum electrodes.
Smaller electrodes increase the applied charge density, potentially damaging the electrode.
Greater understanding of the charge injection mechanism is required for safe neural stimulation.
Approach. The charge injection mechanism and charge injection capacity were measured by
cyclic voltammetry. Electrodes were cleaned mechanically or by potential cycling in acidic
solutions. The effective electrode area was measured by hydrogen adsorption or reduction
6 . Main results. The water window and safe potential window were affected by
changes to electrolyte, electrode size, polishing method and oxygen concentration. Capacitance
and Faradaic current contribute to the charge injection capacity. Varying voltammetric scan
rate (measurement time), electrode size, polishing method, potential window, electrolyte and
oxygen concentration affected the charge injection capacity and ratio of oxidation to reduction
charge. Hydrogen adsorption in acidic solutions provided an inaccurate effective electrode
area. Reduction of a solution phase redox species with a linear or radial diffusion profile could
provide an effective electrode area. The charge density (charge injection capacity divided
by electrode area) of a platinum electrode is dependent on the charge injection capacity and
electrode area measurement technique. By varying cyclic voltammetric conditions, the charge
density of platinum ranged from 0.15 to 5.57 mC cm−2
. Significance. The safe potential
window, charge injection mechanism, charge injection capacity and charge density of platinum
depends on electrolyte, size of the electrode, oxygen concentration and differences in electrode
polishing method. The oxidation and reduction charge injection capacities are not equal.
Careful control of a platinum electrodes surface may allow larger charge densities and safe use
of smaller electrodes. New electrode materials and geometries should be tested in a consistent
manner to allow comparison of potential suitability for neural stimulation.