What Is a Galvanostat?
A galvanostat is a device in electrochemistry.
This device applies a voltage to a sample to induce a chemical reaction or to detect a change in a physical quantity caused by a chemical reaction. Galvanostats are commonly used in combination with potentiostats, which are also measuring devices in electrochemistry.
These two devices control a cell containing three types of electrodes: a sample electrode, a counter electrode, and a reference electrode. What is controlled by potentiostats and Galvanostats is different, with the former controlling voltage and the latter controlling current.
Applications of Galvanostats
Galvanostats are used in chronopotentiometry and battery discharge testing.
1. Chronopotentiometry
Chronopotentiometry is a method of measuring data by tracking changes in electric potential over time. Generally, a constant current is applied to the sample electrode and parameters related to electrochemical reactions are obtained with no flow between the sample electrode and the electrolyte.
The parameters obtained include the concentration of substances involved in the redox reaction and the diffusion coefficient. To handle the redox reaction of the components present in the electrolyte, platinum is used as the electrode for this measurement, as it does not easily dissolve into ions.
2. Battery Discharge
There are primary and secondary batteries. Primary batteries are used-up batteries and can only be discharged. Secondary batteries, on the other hand, can be discharged and recharged, and can be used repeatedly.
Galvanostats are used to evaluate discharge and recharge performance. Lithium-ion batteries are examples of rechargeable batteries. Lithium-ion batteries are used in smartphones and hybrid vehicles.
Principle of Galvanostat
Galvanostat requires a signal generator and a PC as well as the object to be measured. A frequency response analyzer (FRA) is used for the signal generator, which adds a sine curve with a constant frequency. The sine curve output from the FRA is input to the Galvanostat to produce a voltage. The voltage generated in the Galvanostat causes a current to flow through the object being measured, and the response signal from the sample is input to the Galvanostat.
The signal input to the Galvanostat is converted to a wave and input to the FRA. At this time, a sin (omega) wave is generated, whose phase is shifted by omega from the input sin wave. The phase shift depends on the object to be measured.
The sin (omega) wave is Fourier transformed in the FRA and only the components of the measurement frequency are extracted. Finally, the data extracted by the Fourier transform is sent to a PC. By monitoring these values, it is possible to quantitatively evaluate the parameters.
Other Information About Galvanostat
1. Principle of FRA
FRA is a device that applies a sinusoidal signal to an object under test and observes its frequency response. FRA uses a digital correlation method called SSC (Single Sine Correlation) to determine the impedance.
FRA is the most widely used measurement method for electrochemical measurement applications, with a basic amplitude accuracy of 0.1% and a basic phase accuracy of 0.1 degree. The response signal returned from the object to be measured is not only the frequency of the input signal, but also includes other frequency components.
In order to obtain only the frequency of the input signal, FRA multiplies the response signal by a sin wave in phase with the input signal and a sine wave with a phase shifted by 90 degrees. By dividing the frequency components into real and imaginary components, it is possible to acquire the same frequency components as the input signal in the response signal.
2. Features of FRA
One of the features of FRA is its excellent noise reduction function: FRA can reduce high-frequency components to -60dB or lower with a single measurement using the single sine correlation method. Further removal of noise components is possible by increasing the number of integrations. Even if the signal to be analyzed has an amplitude below the noise, it can still be extracted.
Another advantage is the wide frequency range (10uHz to 1MHz) over which it can measure. Since the signal is digitally processed including the output of the internal oscillator, there is no waveform distortion.