Electron transfer processes occurring on platinum neural stimulating electrodes: a tutorial on thei(V_e) profile

Abstract

The aim of this tutorial is to encourage members of the neuroprosthesis community to incorporate electron transfer processes into their thinking and provide them with the tools to do so when they design and work with neurostimulating devices. The focus of this article is on platinum because it is the most used electrode metal for devices in commercial use. The i(V e) profile or cyclic voltammogram contains information about electron transfer processes that can occur when the electrode-electrolyte interface, V e, is at a specific potential, and assumed to be near steady-state conditions. For the engineer/designer this means that if the potential is not in the range of a specific electron transfer process, that process cannot occur. An i(V e) profile, recorded at sweep rates greater than 0.1 mVs(-1), approximates steady-state conditions. Rapid transient potential excursions, like that seen with neural stimulation pulses, may be too fast for the reaction to occur, however, this means that if the potential is in the range of a specific electron transfer process it may occur and should be considered. The approach described here can be used to describe the thermodynamic electron transfer processes on other candidate electrode metals, e.g. stainless steel, iridium, carbon-based, etc.

Electron transfer processes occurring on platinum neural stimulating electrodes: calculated charge-storage capacities are inaccessible during applied stimulation

“…For a comprehensive explanation of the theory behind i-E curves (or i-V e profiles, cyclic voltammograms) and how to record and interpret them, see our previous publication. [34] Typical platinum behavior was indicated by the observed current peaks: oxide formation and reduction, atomic hydrogen (H) adsorption and desorption, and molecular hydrogen (H 2 ) evolution and desorption. For the i-E curve in figure 2a, the cathodic charge transfer associated with double-layer charging and the hydrogen adsorption reactions in the region between −0.22 V and +0.05 V (blue shaded area) was calculated to be 698 µC/cm 2 .…”

A low-cost, scalable, current-sensing digital headstage for high channel countμECoG

“…When measuring extracellular fields, however, it is customary to use voltage amplifiers that have high input impedance (reducing the current in the electrode) rather than current amplifiers with virtually zero input impedance. It is well known with voltage-controlled neural stimulation that the electrode-electrolyte interface impedance creates a complex-valued load that transforms the resulting current in a time- and frequency-dependent manner [21, 22]. A voltage pulse must be pre-compensated to deliver the desired current pulse [23].…”

Electrochemistry of Graphene Nanoplatelets Printed Electrodes for Cortical Direct Current Stimulation

“…(Harris et al, 2018) and thus may cause various types of tissue damage (Kumsa et al, 2019). For example, molecular oxygen that evolved due to oxidation of water (Kumsa et al, 2016) may in turn lead to oxidation of tissue. Other mechanisms may lead to electrochemical production of toxic species (Fridman and Santina, 2013) or forced activation of cells that cannot withstand high levels of stimulation (Günter et al, 2019).…”