This is generally in systems which exhibit very low currents or relatively short timescales and which also have a well-poised counter, e.g., a micro working electrode and a much larger silver counter electrode. The other is where the counter-electrode potential can be expected not to drift over the course of the experiment.
One is where measurement of the whole cell voltage is significant, for example electrochemical-energy devices (e.g., batteries, fuel cells, supercapacitors). Two-electrode setups are used in a couple of general cases. The Working lead is at point A and the Counter lead is at point E. If a map of the whole-cell potential looks like Figure 3, then a 2-electrode setup has the Working Sense lead at point A and the Reference lead at point E, and so measures the voltage drop across the whole cell.įigure 3: Measured (sample) potential map across a whole cell. Two-electrode experiments measure the whole cell, that is, the sense leads measure the complete voltage dropped by the current across the whole electrochemical cell: working electrode, electrolyte, and counter electrode. See Figure 2 for a diagram of a 2-electrode cell setup. The physical setup for two-electrode mode has the current and sense leads connected together: Working (W) and Working Sense (WS) are connected to a (working) electrode and Reference (R) and Counter (C) are connected to a second (aux, counter, or quasi-/pseudo-reference) electrode. In a two-electrode setup the current-carrying electrodes are also used for sense measurement. Two-electrode experiments are the simplest cell setups, but often have far more complex results, and corresponding analysis. There are other couples that are often referenced but are not typically used today, such as the normal hydrogen electrode.Īny conductive material can be used as a reference electrode, but if potential measurements are to be reported that need to be compared with other systems, use of a non-standard reference requires additional experimentation and explanation. While many electrodes could be well-poised, there are several that are very commonly used and commercially available: silver/silver chloride, saturated calomel, mercury/mercury (mercurous) oxide, mercury/mercury sulfate, copper/copper sulfate, and more. This is accomplished by first having little or, ideally, no current flow through them, and second by being “well-poised,” which means that even if some current does flow it does not affect the potential. Reference electrodes should, therefore, hold a constant potential during testing, ideally on an absolute scale. Specifically, they are a reference for the potential (sense) measurements. Reference electrodes are, as their name suggests, electrodes that serve as experimental reference points. In some experiments the counter electrode is part of the study, so the material composition and setup vary accordingly. In most experiments the Counter is the current source/sink and so relatively inert materials like graphite or platinum are ideal, though not necessary.
All electrochemistry experiments (with non-zero current) must have a working–counter pair. The Counter or Auxiliary electrode is the electrode in the cell that completes the current path. In physical-electrochemistry experiments, this is most often an inert material-commonly gold, platinum or carbon-which passes current to other species without being affected by that current. In corrosion experiments, this is probably the material that is corroding. Working electrode is the designation for the electrode being studied. The common designations are: Working, Reference and Counter (or Auxiliary). An electrode is a (semi-)conductive solid that interfaces with a(n) (electrolyte) solution. The discussion of n-electrode mode experiments needs to address what the electrodes are.
#Platinum notes 43 how to
Understanding why and how to use the different modes thus is important. Four-probe instruments can be setup to run 2, 3, or 4 electrode measurements with just a simple change in setup.