The Value of Stack Mode Measurements

Introduction

Some researchers want to be able to apply or measure voltages larger than 12 V. One example of the need for larger potentials is battery testing, while another might be CV inside small microfluidic channels. Perhaps you want to perform certain types of electrodeposition experiments.  In these instances you may need to look a little harder for a potentiostat that can operate at these higher voltages.

All Reference™ 3000 potentiostats are able to measure and apply voltages and currents up to the compliance limit. The compliance limit is the output limit of the control amplifier. What is the control amplifier?  The control amplifier is an operational amplifier within the potentiostat used to drive the counter electrode in order to achieve the desired voltage between a reference electrode and a working electrode. Higher power means larger voltages and currents, but this comes at a cost though: more power means more heat dissipation, larger instruments, and additional cost. 

For those that need higher voltages, the Reference 3000 has some unique advantages you should know and understand. The Reference 3000 has two compliance ranges: ±15 V at ±3 A, or ±32 V at ±1.5 A. Under normal circumstances, the Reference 3000 can apply and measure up to 12 V. This is done in the 15 V compliance range. Connections to the cell are standard and shown in Figure 1A. Working/Working sense leads are connected to the Working electrode; the Counter lead attaches to the Counter electrode, and the Reference lead goes to the Reference electrode. In two-electrode mode, the Working and Working Sense are connected to the working electrode and the Reference and Counter are connected to the counter electrode as show in Figure 1B.

working electrode counter electrode connection

Figure 1. Normal operation of a Reference™ 3000 in 3-electrode (A) or 2-electrode (B) modes.
Voltages < ±12 V. Reference lead is connected to Floating Ground.  

 

Software Version 6

In Version 6.x of Gamry Instruments’ Framework™ software, when running experiments contained in the Electrochemical Energy submenu, there are three choices for cell type: Half, Full, and Stack. Half (3-electrode) and Full (2-electrode) cell types correspond to the situation described above where voltages can be applied or measured up to 12 V. Connections are as shown in Fig. 1. When selecting Stack mode to reach higher voltages, follow the procedure as outlined below. 

Voltages > 12 V but < 15 V: Low Compliance

To go beyond 12 V requires Stack Mode. In Stack Mode, the Reference 3000 is measuring the potential difference between the Counter Sense and the Working Sense. The Reference lead is not used in this setup; connect the Reference lead to the Floating Ground lead via a 2 mm pin adapter. For 3-electrode mode, connect the Working and Working Sense leads to the working electrode, Counter Sense lead to the reference electrode, and Counter lead to the counter electrode as shown in Figure 2A. For 2-electrode mode, connect the Working and Working Sense leads to the working electrode and the Counter and Counter Sense leads to the counter electrode as shown in Figure 2B.  

2 electrode mode

Figure 2. Stack mode operation (low compliance) of a Reference™ 3000 in 3-electrode (A) or 2-electrode (B) modes.
Voltages > 12 V but < 15 V. Reference lead is connected to Floating Ground.  

Voltages > 15 V: High Compliance

Applying and measuring voltages larger than 15 V requires switching to High Compliance. This is done through the Utilities submenu. In the Framework software, choose Experiment > Utilities and click Compliance Voltage. A Compliance Voltage Setting dialog box opens:

compliance voltage setting

Select the radio button for the desired Reference 3000, and then click the OK button. A new window appears, which lets you select Low or Hi:

hi low compliance voltage setting

Click the Hi radio button, and then click OK. The instrument is now in high compliance mode.

For 3-electrode mode, connect the Working and Working Sense leads to the working electrode, Counter Sense lead to the reference electrode, and Counter lead to the counter electrode as shown in Figure 3A. For 2-electrode mode, connect the Working and Working Sense leads to the working electrode, and the Counter and Counter Sense leads to the counter electrode as shown in Figure 3B.

Stack Mode Operation

Figure 3. Stack mode operation (low compliance) of a Reference™ 3000 in 3-electrode (A) or 2-electrode (B) modes.
Voltages > 15 V. Reference lead is connected to Floating Ground.  

 

Software Version 7

Version 7 of our Framework software changes the Cell Type selection to Half (3-electrode), Full (2-electrode), and Both in the Electrochemical Energy experiments. The setup box explicitly asks you for your expected maximum voltage. The software automatically chooses Low Compliance or High Compliance based upon your input. If desired, the software can show a dialog box that describes the cable connections to your cell if you activate the Cable Check checkbox. 

Selecting Both is only valid for the Interface 5000.  Selecting Both for the Interface 1000 or a Reference family instrument will result in an error message.  

High-voltage Experiments not in Electrochemical Energy

Some researchers may want higher voltages for experiments that are not part of the experiments in Electrochemical Energy submenu. For these researchers, use the following procedure. All experiments are written in our Open Source Scripting language, Explain™. Users are able to modify these scripts as needed.

Each experimental script contains an initialize function for the potentiostat. Within this function, you can add lines of code to select Stack Mode and either High Compliance or Low Compliance. Below is the line for setting the compliance mode.  

setElectrometer

 

You can also change the compliance mode using the Utilities submenu as discussed earlier. Modifying the script will ensure the compliance mode is always set according to your needs.

Change the Pstat.SetCtrlMode line in the InitializePstat function found at the bottom of each experimental script file to:

Pstat.SetCtrlMode (ZraX4Mode)

This turns on Stack Mode. 

Next, you must create a new global variable. This variable is used to rescale the voltage values displayed during acquisition.  For example, you could use “multiplier” as your variable. There are four places you need to add the multiplier variable. Look for ‘; Run the curve’ in the script you want to modify, e.g., in Chronoamperometry.exp. Each voltage must be multiplied by the variable.

Vpresetep.VsEref () * multiplier

Vstep1.VsEref () * multiplier

Vstep2.VsEref () * multiplier