Variedad, características y formas de los electrodos de trabajo.
| Variedad de electrodos de trabajo | Características y aplicaciones |
| Electrodo de platino (PTE) |
Electrodo convencional, que tiene una onda de adsorción de hidrógeno, utilizado para la detección de H 2 O 2 y óxidos |
| Electrodo de oro (AUE) |
Electrodo convencional, que no tiene onda de adsorción de hidrógeno, utilizado para la detección de tioles |
| Electrodo de carbono vítreo (GCE) |
Electrodo químicamente estable a pesar de sus sobre-potenciales relativamente grandes de las evoluciones de oxígeno e hidrógeno. |
| Electrodo de plata (EDAD) |
Para la detección de cianuro y sulfuro. |
| Electrodo de pasta de carbono (CPE) |
Mezclado con enzima etc. para hacer electrodos modificados. |
| 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
Potential Window of Pt‚ Hg‚ Carbon electrodes in aqueous solution
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
David K.Gosser,Jr.,Cyclic Voltammetry Reaction
Mechanisms,VCH Publishers,Inc. 1994.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,El sobrepotencial de hidrógeno / oxígeno no afecta. En lugar de eso, el potencial de descomposición del solvente no acuoso y el electrolito de soporte constituye un factor importante. Además, la impureza del agua en un disolvente no acuoso hace que la ventana de potencial sea más estrecha dependiendo de la cantidad de agua.
Figura: Bordes de corriente-potencial del resultado de escanear 50 veces sumergiendo un electrodo de Pt en una solución de0,5 MH 2SO 4 . La repetición del ciclo obviamente activa el electrodo. Aunque hay una onda de absorción en el lado del cátodo, es posible observar otra reacción de los electrodos en este rango de potencial porque esta reacción requiere solo cierta cantidad de electricidad.
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.
Akira Fujishima, Toru Inoue, Method of Electrochemical measurement, Gihodo Publishers, 1984.
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
David K.Gosser,Jr.,Cyclic Voltammetry Reaction
Mechanisms,VCH Publishers,Inc. 1994.
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,El sobrepotencial de hidrógeno / oxígeno no afecta. En lugar de eso, el potencial de descomposición del solvente no acuoso y el electrolito de soporte constituye un factor importante. Además, la impureza del agua en un disolvente no acuoso hace que la ventana de potencial sea más estrecha dependiendo de la cantidad de agua.
Figura: Bordes de corriente-potencial del resultado de escanear 50 veces sumergiendo un electrodo de Pt en una solución de0,5 MH 2SO 4 . La repetición del ciclo obviamente activa el electrodo. Aunque hay una onda de absorción en el lado del cátodo, es posible observar otra reacción de los electrodos en este rango de potencial porque esta reacción requiere solo cierta cantidad de electricidad.
Ventajas del uso de microelectrodos para la medición de CV.
| 1. Poca distorsión por disipación en el potencial o flujo de electrificación 2. La combinación de PC permite procesar a alta velocidad de barrido 3. Intermedio de corta duración analizable en la reacción del electrodo 4. Medible sin electrolito de soporte 5. Excelente precisión de medición debido a la poca influencia del ruido Derivado del flujo de electrificación 6. Difusión suave suficiente para obtener un estado estacionario |
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Figura en la derecha: el resultado de la detección de un producto químico en la reacción posterior. Mediante el barrido más rápido a 10 4 V / S, el pico (que se muestra cuando el intermedio de corta duración se reduce a la sustancia anterior ) se puede observar antes de que desaparezca el intermedio . Kosuke Izutsu, Electroquímica en soluciones no acuosas , WILEY-VCH, 2002. |