TITLE: Electrochemical analysis of laser-inscribed graphene electrodes using cyclic voltammetry (ferri/ferrocyanide redox couple)
AUTHORS: Yifan Tang, Lisseth Casso Hartmann, David Bahamon Pinzon, Geisianny AM Moreira, Diana Vanegas, Eric S McLamore

[DESCRIPTION]
This protocol describes use of the cyclic voltammetry (CV) method for electrochemical analysis of laser-inscribed graphene (LIG) electrodes. The protocol requires approximately 1 hour (excluding electrode fabrication).

[BEFORE_START]
Always wear proper PPE during experiment (gloves, eyewear, lab coat, proper clothing)

[GUIDELINES]
The steps for the process are summarized in Figure 1. The protocol is based on numerous published manuscripts that use similar methods with the ferri/ferrocyanide redox couple (REF 1-4), but is not a comprehensive guide. Where appropriate, alternative redox couples or electrolytes are noted.
  


[STEPS]
SECTION: Preparation
1. Prepare LIG electrodes 
Use protocol for LIG fabrication to prepare a batch of electrodes (link here).
For quality control process to prepare large batches of LIG electrodes, contact the corresponding author (emclamo@clemson.edu). 
 

Expected results from step 1:
Fig 1 shows photographs of the instrument and the expected results from a batch fabrication of six replicate electrodes based on the LIG fabrication protocol here 
  
 

SECTION: Preparation
2. Prepare solution
Gather a sealed glass storage bottle or Falcon tube with at least 50 mL of capacity and label as 2.5 mM ferri/ferrocyanide + 100mM KCl. The masses below are for preparation of a 50mL solution.
In a separate weigh boat/paper, prepare the following:
                1-Weigh 52.8 mg potassium ferricyanide (2.5 mM K4[Fe(CN)]6) on a scale.
                2-Weigh 41.2 mg potassium ferrocyanide (2.5 mM K₃[Fe(CN)]₆) on a scale.
                3-Weigh 373 mg potassium chloride (KCl) on a scale.
Add the three powders to the labeled glass bottle
Fill glass storage bottle to 50mL with DI water (or nano-pure water)containing 10mL 

 

Place clean magnetic stir bar in bottle and place on a stir plate
Stir for 5 minutes at 1,500 rpm
After mixing, inspect the bottle to ensure dissolution
Transfer 20 mL of the solution to the electrochemical cell (20 mL cell shown in Fig 2)
Prior to analysis, inspect the solution to ensure the color is appropriate. The solution should be yellow in color (not clear). If preferred, a cell phone app may be used to detect the color of the electrolyte. For example, Color Name AR is a helpful tool for color analysis that is available for both iPhone and Android systems (https://apps.apple.com/us/app/color-name-ar/id906955675). 

 

 

SECTION: Electrochemical testing
3. Connect electrodes
 

Assemble electrochemical cell (Benchtop Palmsens4 system):

Single electrode system
Connect the single LIG electrode with the potentiostat via the bonding pads using alligator clips
Ensure the electrodes are not touching, and the distance between the auxiliary and working electrodes is consistent. 
Fig 2A shows the correct assembly of the electrochemical cell for a single LIG "dip-style" electrode, where a Ag/AgCl reference electrode and Pt wire are used as reference and counter electrode, respectively

Three electrode (chip) system
Connect the USB adapter to the chip directly, and position the LIG chip in the electrochemical cell using the QuadHands magnetic workbench (Fig 2B). 
For connecting the chip system, a female USB type A connector is used as described in the LIG fabrication protocol (see Fig 2C). 

  

 


Assemble electrochemical cell (ABE STAT portable system):
The ABE-STAT contains indicators for connections of working (W), counter (C) and reference (R) electrodes (Fig 3A). 
Connect the electrodes accordingly, as described previously. Fig 3B shows an example of an experimental setup using a three-electrode chip.
The electrodes are positioned in the electrochemical cell using the QuadHands magnetic workbench. 
A single electrode, or chip system may be developed for ABE-STAT, as shown in Fig 2.

  
SECTION: Electrochemical testing
4. Conduct scan (PalmSens4 benchtop system)
 

Turn on Palmsens hardware and the computer. 
Open the PalmSens software (MultiTrace4 software).
Users may operate 3 channels simultaneously or individually (Fig 4C)Select Cyclic Voltammetry as the Technique (Fig 4D). After selecting the mode, set up all parameters. For example, see settings below (see MultiTrace manual for details; link here)

 

Expected results from PalmSens4 benchtop potentiostat
Fig 4 shows the channels connections to the PalmSens, mode selection panel, and operation panel.
When the experiment finishes, click export to excel icon to export data.
When exporting data, make sure all channels' data are exported.
SECTION: Data analysis
5. Analyze CV data 
CV data are commonly analyzed to produce the following outcomes. References are provided for details of calculations.
Electroactive surface area 8
Charge, if a pseudo-capacitor or capacitor 9

Expected results
Fig 8 shows a representative cyclic voltammogram for a single LIG electrode.
 
 


SECTION: Clean up
6. Clean workspace (Timing: 5 min)
Ensure chemicals are stored or discarded correctly, and turn off Palmsens and the computer.
If using external reference and auxiliary electrodes, clean them up with DI water and store them in the appropriate place. Reference electrodes should be stored with a 3M KCl solution.
Wipe the working desk with 75 % alcohol. 
Store electrodes when not in use.
SECTION: Data Management
7. 


File naming: For files from CV analysis, the following naming system was utilized:
DATA_CV1.1

File storage: Store all methods in the Desktop folder with the operator's name clearly identified in the folder name.

Backup files: At least once per year, ensure that the folder is backed up on the lab's external hard drive.