The electrode where oxidation occurs in an electrochemical cell. By common convention, the current on the anode is considered a positive current; however, in electroanalytical chemistry the anodic current is often considered negative.
See counter electrode
A potentiostat that controls the potential of two working electrodes independently in the same cell Mainly used for rotating-ring-disk electrodes.
The electrode where reduction occurs. It is negative in an electrolytic cell, but positive in a galvanic cell. By common convention, the current on the cathode is considered a negative current; however, in electroanalytical chemistry the cathodic current is often considered positive.
The electrical potential difference between the two electrodes of an electrochemical cell. For a three-electrode cell, it is the voltage between the working electrode and the counter electrode. The cell voltage ishould not be confused with the working electrode potential.
A chemical reaction where electrical charges are passed from one reactant to another. If the charge is passed from an electrode to a dissolved species, it is considered as a heterogeneous charge-transfer reaction.
An electrochemical technique used for analysis or for kinetics studies. The potential of the working electrode of an electrochemical cell is rapidly changed by a rectangular pulse, and the resulting current is measured as a function of time. See Cottrell equation.
An electrochemical technique used for analysis or for kinetics studies. The potential of the working electrode of an electrochemical cell is rapidly changed by a rectangular pulse, and the resulting charge is measured as a function of time.
An electrochemical technique used for analysis or for kinetics studies. The current through the working electrode of an electrochemical cell is rapidly changed by a rectangular pulse, and the resulting potential is measured as a function of time. See Sand equation.
The corrosion current per area unit (current density) is directly proportional to the corrosion rate. See also Tafel plot.
The rest potential of a corroding material is also called corrosion potential. It is a mixed potential with a value between the equilibrium potentials of the anodic and cathodic corrosion reactions.
The C. describes the relation between diffusion limited current and time in a chronoamperometry. It is valid if the potential jump is large enough to result immediately in limiting current. It is applicable to planar electrodes in unstirred solutions only. Simplified, it says that i(t) × t0.5 is a constant.
Coulometer
Also designed as Integrator: used to measure the electrical charge
Coulometry see Chronocoulometry
The counter electrode is an auxiliary electrode which shall not react with the electrolyte. It is only used to force a current through the working electrode. It is made of inert materials (Pt, Au, Graphite, or platinised Ti). Also called auxiliary electrode.
Current Density
The electrochemical reaction rate is defined by the current I passing an electrode, divided by the electrode area: This is the current density (abbr. i)
A current sink is an ampere meter which has practically no internal resistance. Therefore, current sinks also are called "zero - ohm - ammeters". Current sinks are valuable if e.g. galvanic currents are to be measured without producing a voltage drop across the ammeter. So, they are capable to measure extremely small currents down below the pA - range.
The electrical potential difference between two solutions separated by an semi-permeable wall (membrane) in the absence of any current flowing through the membrane.
Double-junction Reference Electrode
A common calomel (or AgCl) electrode is contained in another vessel containing a chloride-free solution (e.g. conc. KNO3) in order to prohibit chloride contamination of the main electrolyte.
An electrometer is a special kind of voltmeter, having extremely high internal resistance (typically > 1000 GOhms). It is used to measure equilibrium potentials.
E.o. is the movement of a liquid through a capillary tubing or porous solid driven by an electrical potential difference
E.p. is the movement of suspended particles in a liquid driven by an electrical potential difference. Used to deposit material on an electrically charged surface in an electrolyte (painting, ceramic coating).
The equilibrium potential is the potential which is established at an electrode as long as a chemical equilibrium is established at the surface of the electrode, and no external current passes the electrode, also called "open circuit potential" OCP.
A very sensitive ammeter used to measure currents in the range of µA down to pA and below.
A galvanostat is a device used to control the electric current passing an electrode. Indeed, each potentiostat can act as galvanostat, depending on the manner to connect the cell. Many of our potentiostats however, can be switched from the potentiostatic to the galvanostatic mode without changing the cell connections.
A salt bridge from the reference electrode to the main electrolyte with a capillary tip at one end. The tip is placed close to the working electrode to minimise IR drop error. Also called Luggin Probe.
The N.E. defines the equilibrium potential of an electrode. E = Eo + (RT/nF) * logQ, where Q is the quotient of oxidised and reduced species.
Normal hydrogen electrode, another name for the standard hydrogen electrode
(abbr.) open-circuit potential.
The difference between the cell voltage, while a current is passing the cell, and the open-circuit voltage
The change of potential of an electrode from its equilibrium potential upon the application of a current. Confusingly, the term "polarisation" is also used in optics and biology, having another meaning then.
Another name for current-potential plot
A potentiostat is a device used to keep a working electrode at desired potential with respect to a reference electrode. This is done by a current which is passed from the working electrode to a counter electrode. From a more electronic point of view, a potentiostat is a special kind of feed-back amplifier.
Usually, reference electrodes have high source resistances: some kOhms up to MOhms. If you use a common voltmeter with an internal resistance of some MOhms, appreciable potential errors may occur.
Potential meters therefore have input resistances of more GOhms.
Polarisation means to force the working electrode from its rest potential (or equilibrium potential) to another potential.
The polarisation resistance is defined by the slope DE / DI of the current - potential curve in the vicinity of the rest potential. It depends on the electrode area and the rate of the potential shift (or current shift) used to measure the curve (see also impedance measurements)
An electroanalytical technique, introduced by J. Heyrovsky, for which he was awarded the Nobel Prize for Chemistry in 1959. It is basically 2-electrode sweep voltammetry using a dropping-mercury electrode for working electrode and a mercury pool as counter electrode.
The voltage difference to a standard level is called potential (abbr. E). In electrochemistry, all potentials refer to the reaction 2H+ + 2 e- ---> H2 at standard conditions (1 molar concentration, 1 bar pressure, 20°C).
Alternative name for linear-sweep voltammetry, mainly used for obtaining polarisation curves at low dE/dt rates.
Measurement of the electromotive force between a working electrode and a reference electrode.
An electronic device controlling the electrical potential between the working electrode and a reference electrodes of a three-electrode cell to a selected value. This condition requires that current is passed through the working electrode. The potentiostatic condition can be established as long as the cell voltage can be established and the required current can be delivered by the potentiostat.
A reference electrode is an electrode which always has a constant electrical potential (you may also say voltage difference) with respect to the standard hydrogen electrode as the reference point for all electrochemical potentials.
The potential of a electrode is called the rest potential (also called open circuit potential), if no externally forced current passes this el
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