Rotating disk electrode
Encyclopedia
A rotating disk electrode (RDE) is a hydrodynamic
working electrode
used in a three electrode system
. The electrode rotates during experiments inducing a flux
of analyte
to the electrode. These working electrodes are used in electrochemical studies when investigating reaction mechanisms
related to redox
chemistry, among other chemical
phenomena. The more complex rotating ring-disk electrode
can be used as a rotating disk electrode if the ring is left inactive during the experiment.
or glassy carbon
, however any conductive material can be used based on specific needs.
is usually described in terms of angular velocity
. As the disk turns, some of the solution described as the hydrodynamic boundary layer is dragged by the spinning disk and the resulting centrifugal force
flings the solution away from the center of the electrode. Solution flows up, perpendicular to the electrode, from the bulk to replace the boundary layer. The sum result is a laminar flow of solution towards and across the electrode. The rate of the solution flow can be controlled by the electrode's angular velocity and modeled mathematically. This flow can quickly achieve conditions in which the steady-state current is controlled by the solution flow rather than diffusion. This is a contrast to still and unstirred experiments such as cyclic voltammetry
where the steady-state current is limited by the diffusion of substrate.
By running linear sweep voltammetry
and other experiments at various rotation rates, different electrochemical phenomena can be investigated, including multi-electron transfer, the kinetics of a slow electron transfer, adsorption/desorption steps, and electrochemical reaction mechanism
s.
are not possible for a RDE system since the products of the potential sweep are continually swept away from the electrode. A reversal would simple produce an i-E curve which exactly matched the initial scan direction. Further complications arise in investigate the reactivity of these products, since they are swept away from the electrode. In contrast, the rotating ring-disk electrode
is well suited to investigate this further reactivity.
Hydrodynamic technique
Hydrodynamic technique is a subcategory of electroanalytical methods in which the analyte solution flows relative to a working electrode. In many voltammetry techniques, the solution is intentionally left still to allow diffusion controlled mass transfer...
working electrode
Working electrode
The working electrode is the electrode in an electrochemical system on which the reaction of interest is occurring. The working electrode is often used in conjunction with an auxiliary electrode, and a reference electrode in a three electrode system...
used in a three electrode system
Voltammetry
Voltammetry is a category of electroanalytical methods used in analytical chemistry and various industrial processes. In voltammetry, information about an analyte is obtained by measuring the current as the potential is varied.- Three electrode system :...
. The electrode rotates during experiments inducing a flux
Flux
In the various subfields of physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks.* In the study of transport phenomena , flux is defined as flow per unit area, where flow is the movement of some quantity per time...
of analyte
Analyte
An analyte, or component , is a substance or chemical constituent that is of interest in an analytical procedure. Grammatically, it is important to note that experiments always seek to measure properties of analytes—and that analytes themselves can never be measured. For instance, one cannot...
to the electrode. These working electrodes are used in electrochemical studies when investigating reaction mechanisms
Electrochemical reaction mechanism
In chemistry, an electrochemical reaction mechanism is the step by step sequence of elementary steps, involving at least one outer sphere electron transfer, by which an overall chemical change occurs .- Overview :...
related to redox
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
chemistry, among other chemical
Chemistry
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
phenomena. The more complex rotating ring-disk electrode
Rotating ring-disk electrode
A rotating ring-disk electrode is double working electrode used in hydrodynamic voltammetry, very similar to a rotating disk electrode . The electrode actually rotates during experiments inducing a flux of analyte to the electrode...
can be used as a rotating disk electrode if the ring is left inactive during the experiment.
Structure
The electrode includes a conductive disk embedded in an inert non-conductive polymer or resin that can be attached to an electric motor that has very fine control of the electrode's rotation rate. The disk, like any working electrode, is generally made of a noble metalNoble metal
Noble metals are metals that are resistant to corrosion and oxidation in moist air, unlike most base metals. They tend to be precious, often due to their rarity in the Earth's crust...
or glassy carbon
Glassy carbon
Glassy carbon, also called vitreous carbon, is a non-graphitizing carbon which combines glassy and ceramic properties with those of graphite. The most important properties are high temperature resistance, hardness , low density, low electrical resistance, low friction, low thermal resistance,...
, however any conductive material can be used based on specific needs.
Function
The disk's rotationRotation
A rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A rotation...
is usually described in terms of angular velocity
Angular velocity
In physics, the angular velocity is a vector quantity which specifies the angular speed of an object and the axis about which the object is rotating. The SI unit of angular velocity is radians per second, although it may be measured in other units such as degrees per second, revolutions per...
. As the disk turns, some of the solution described as the hydrodynamic boundary layer is dragged by the spinning disk and the resulting centrifugal force
Centrifugal force
Centrifugal force can generally be any force directed outward relative to some origin. More particularly, in classical mechanics, the centrifugal force is an outward force which arises when describing the motion of objects in a rotating reference frame...
flings the solution away from the center of the electrode. Solution flows up, perpendicular to the electrode, from the bulk to replace the boundary layer. The sum result is a laminar flow of solution towards and across the electrode. The rate of the solution flow can be controlled by the electrode's angular velocity and modeled mathematically. This flow can quickly achieve conditions in which the steady-state current is controlled by the solution flow rather than diffusion. This is a contrast to still and unstirred experiments such as cyclic voltammetry
Cyclic voltammetry
Cyclic voltammetry or CV is a type of potentiodynamic electrochemical measurement. In a cyclic voltammetry experiment the working electrode potential is ramped linearly versus time like linear sweep voltammetry. Cyclic voltammetry takes the experiment a step further than linear sweep voltammetry...
where the steady-state current is limited by the diffusion of substrate.
By running linear sweep voltammetry
Linear sweep voltammetry
Linear sweep voltammetry is a voltammetric method where the current at a working electrode is measured while the potential between the working electrode and a reference electrode is swept linearly in time...
and other experiments at various rotation rates, different electrochemical phenomena can be investigated, including multi-electron transfer, the kinetics of a slow electron transfer, adsorption/desorption steps, and electrochemical reaction mechanism
Electrochemical reaction mechanism
In chemistry, an electrochemical reaction mechanism is the step by step sequence of elementary steps, involving at least one outer sphere electron transfer, by which an overall chemical change occurs .- Overview :...
s.
Limitation
Potential sweep reversals as used in cyclic voltammetryCyclic voltammetry
Cyclic voltammetry or CV is a type of potentiodynamic electrochemical measurement. In a cyclic voltammetry experiment the working electrode potential is ramped linearly versus time like linear sweep voltammetry. Cyclic voltammetry takes the experiment a step further than linear sweep voltammetry...
are not possible for a RDE system since the products of the potential sweep are continually swept away from the electrode. A reversal would simple produce an i-E curve which exactly matched the initial scan direction. Further complications arise in investigate the reactivity of these products, since they are swept away from the electrode. In contrast, the rotating ring-disk electrode
Rotating ring-disk electrode
A rotating ring-disk electrode is double working electrode used in hydrodynamic voltammetry, very similar to a rotating disk electrode . The electrode actually rotates during experiments inducing a flux of analyte to the electrode...
is well suited to investigate this further reactivity.
See also
- working electrodeWorking electrodeThe working electrode is the electrode in an electrochemical system on which the reaction of interest is occurring. The working electrode is often used in conjunction with an auxiliary electrode, and a reference electrode in a three electrode system...
- voltammetryVoltammetryVoltammetry is a category of electroanalytical methods used in analytical chemistry and various industrial processes. In voltammetry, information about an analyte is obtained by measuring the current as the potential is varied.- Three electrode system :...
- hydrodynamic techniqueHydrodynamic techniqueHydrodynamic technique is a subcategory of electroanalytical methods in which the analyte solution flows relative to a working electrode. In many voltammetry techniques, the solution is intentionally left still to allow diffusion controlled mass transfer...
- rotating ring-disk electrodeRotating ring-disk electrodeA rotating ring-disk electrode is double working electrode used in hydrodynamic voltammetry, very similar to a rotating disk electrode . The electrode actually rotates during experiments inducing a flux of analyte to the electrode...
- Levich equationLevich equationThe Levich Equation models the diffusion and solution flow conditions around a Rotating disk electrode . It is named after Veniamin Grigorievich Levich who first developed an RDE as a tool for electrochemical research...