Quick Check of EIS System Performance

The maximum frequency is an important specification for an instrument used to perform Electrochemical Impedance Spectroscopy (EIS). The majority of EIS manufacturers specify a maximum frequency of 1 MHz. Some manufacturer's specifications, however, misrepresent true system performance. Many EIS instruments specified to measure impedance at 1 MHz can apply a 1 MHz signal and measure a response -- but have huge errors when they do so. This document is a protocol to quickly assess the performance of any EIS instrument. You can use it as an easy and effective comparison between systems. You should test before you buy! The test routine involves measuring five EIS spectra. Three spectra are recorded using resistors with ideal EIS response. Two other spectra probe the limits of an EIS system. One spectrum is recorded in potentiostatic mode on a cell that approximates infinite impedance. The second spectrum is recorded in galvanostatic mode on a cell with close to zero impedance. Gamry Instruments will be happy to provide three ± 1% accurate resistors and a piece of braided copper for the near-zero impedance test. Simply call or email us and ask for the "EIS Test Resistors". All high quality EIS systems should allow 4-terminal connections to the cell. In this common scheme, four leads are connected to the sample being tested. Two leads apply current and two leads measure voltage. Impedance is calculated by dividing the measured voltage by the current. EIS spectra cannot be measured accurately without a 4-terminal connection.