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Measuring the effective area and charge density of platinum electrodes for bionic devices

Journal Article


Abstract


  • 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

    of Ru(NH3)

    3+

    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.

Publication Date


  • 2018

Citation


  • Harris, A. R., Newbold, C., Carter, P., Cowan, R. & Wallace, G. G. (2018). Measuring the effective area and charge density of platinum electrodes for bionic devices. Journal of Neural Engineering, 15 (4), 046015-1-046015-12.

Start Page


  • 046015-1

End Page


  • 046015-12

Volume


  • 15

Issue


  • 4

Place Of Publication


  • United Kingdom

Abstract


  • 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

    of Ru(NH3)

    3+

    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.

Publication Date


  • 2018

Citation


  • Harris, A. R., Newbold, C., Carter, P., Cowan, R. & Wallace, G. G. (2018). Measuring the effective area and charge density of platinum electrodes for bionic devices. Journal of Neural Engineering, 15 (4), 046015-1-046015-12.

Start Page


  • 046015-1

End Page


  • 046015-12

Volume


  • 15

Issue


  • 4

Place Of Publication


  • United Kingdom