Technical Notes

Variety, Features and Shapes of Working electrodes

Glassy Carbon Electrode
 
Variety of Working Electrodes Features and Applications
Platinum electrode
(PTE)		 Conventional electrode, which has hydrogen adsorptive wave, used for H2O2 and oxides detection
Gold electrode
(AUE)		 Conventional electrode, which has no hydrogen adsorption wave, used for thiols detection
Glassy carbon electrode
(GCE)		 Chemically stable electrode despite its relatively large over-potentials of oxygen and hydrogen evolutions
Silver electrode
(AGE)		 For cyanide and sulfide detection
Carbon paste electrode
(CPE)		 Mixed with enzyme etc. to make modified electrodes
Nickel electrode
(NIE)		 Chemically modified to detect amino acids
Palladium electrode
(PDE)		 Used to study the process of adsorption and desorption of hydrogen
Plastic formed carbon electrode
(PFCE)		 Its highly-oriented graphite edge is exposed to the surface with cost effective, similar feature of HOPG

 

 

Working Electrodes for Electrochemical Measurements

Our electrodes used for electrochemical measurements such as CV, LSV , DPV and so on are compact and easy enough to be polished by yourself.
Remove the cap covering the electrode, and check its surface prior to the first use. Carbon paste electrode is available in the form of carbon paste which user packs into a shallow well in the electrode holder supplied by us. Other electrodes are polished to immediate use. These electrodes are encapsulated in PEEK* - solid, well inert against solvent. Table of material inertness to solvents is shown below. However, long-term immersion in tetrahydrofuran or using under higher temperature which exceeds the temperature coefficient between plastic and electrode material might be a cause of crack. O-ring enables a position of an electrode to be adjusted in the voltammetry cell.
 

Material Inertness to Solvents

 

 
Potential Window of Pt‚ Hg‚ Carbon electrodes in aqueous solution

 

potential window
Akira Fujishima, Toru Inoue, Method of Electrochemical measurement, Gihodo Publishers, 1984.
 
The figure below shows the appropriate materials of the electrodes to research at some potential range. To analyze the redox activity of a substance dissolved in a kind of aqueous electrolyte with certain pH, it is indispensable to consider about hydrogen over of the electrode, oxygen over voltage and dissolution potential.
 

 

 
What is CV (Cyclic Voltammetry) Measurement?

 

Linear Sweep Voltammetry (LSV) measures the electric response with sampling it at a constant scan rate from initial to final electric potential.

Cyclic voltammetry (CV) is a reversible LSV measurement which scans electric potential turned to reverse direction after reaching final potential and scan back to initial potential. In CV, the reversibility of the product produced in forward scanning can be analyzed by backward scanning. Because of this characteristic, CV has been applied widely. If a CV conducts with potential wave form as shown in right, then we can study the substance characteristic as:

- Stability in oxidized and reduced forms
- Molecular adsorption in redox process
- Measurements of kinetic rate constants
- Study of reaction mechanism
- Reversibility of electrochemical reaction
- Standard redox potential, Eo=(Epa+Epc)/2
- Electron transfer number, ΔE=Epa-Epc= 58/n
*n: electron transfer number per mole
 
CV Measurement Structure

David K.Gosser,Jr.,Cyclic Voltammetry Reaction
Mechanisms,VCH Publishers,Inc. 1994.

 

 

 
Working electrode selection

 

Choice of working electrode is a vital component for experiment.
Redox potential of molecule under research have to fall in the potential window over which the background current due to the electrode itself must not disturb the experiment.

Pt (Platinum) and Au (Gold) electrodes - applied to organic or inorganic substances measurement because they have high overpotential for oxygen evolution and low overpotential for hydrogen evolution.

Hg (Mercury) electrode - well suited to measure reduction of metal ions because of its high overpotential for hydrogen evolution. Hg electrode can easily observe the reduction of Zn.

At the measurement with non-aqueous solvent, hydrogen/oxygen overpotential does not affect. Instead of that, decomposition potential of the non-aqueous solvent and supporting electrolyte comes to an important factor. Furthermore, impurity of water in non-aqueous solvent makes the potential window narrower depending on the quantity of the water.
 
 

 

 

i-E Curbs
 

Figure: Current-Potential curbs of the result of 50 times scanning by immersing a Pt electrode in 0.5 M H2SO4 solution. Reiteration of the cycle obviously activates the electrode. Although there is absorption wave at the cathode side, it is possible to observe other reaction of the electrodes in this potential range because this reaction requires only certain quantity of electricity.
 

 

 
Micro electrodes

Advantages of Microelectrodes use for CV measurement

Micro Pt electrode 10µm
 
1. Little distortion from dissipation in potential or electrification flow
2. Combination of PC enables to process at high sweep rate
3. Analyzable short-lived intermediate in electrode reaction
4. Mearsurable without support electrolyte
5. Excellent measuring accuracy because of little influence of noise arising from electrification flow
6. Smooth diffusion enough to obtain stationary state		  

 

E(V) vs Ag/Ag+     Figure in right : the result of
detection of a chemical product
in subsequent reaction. By the
faster sweep at 104 V/S, the peak
(which is shown when the
short-lived intermediate is
reduced into the former
substance) can be observed
before the intermediate
vanishes.


Kosuke Izutsu, Electrochemistry in Nonaqueous
Solutions, WILEY-VCH, 2002.