WordNet

refer to; "he referenced his colleagues work" (同)cite
the act of referring or consulting; "reference to an encyclopedia produced the answer" (同)consultation
the most direct or specific meaning of a word or expression; the class of objects that an expression refers to; "the extension of `satellite of Mars is the set containing only Demos and Phobos" (同)denotation, extension
a publication (or a passage from a publication) that is referred to; "he carried an armful of references back to his desk"; "he spent hours looking for the source of that quotation" (同)source
the relation between a word or phrase and the object or idea it refers to; "he argued that reference is a consequence of conditioned reflexes"
a conductor used to make electrical contact with some part of a circuit
supported with written references or citations; "a carefully referenced biography"

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〈U〉(…へ)『言及すること』,(…の)話に触れること《+『to』+『名』》;〈C〉言及した事柄 / 〈U〉(…を)『参照すること』,参考《+『to』+『名』》;〈C〉(本などの)出典,参考書;(出典などの)注記 / 〈C〉(人物・才能などの)証明書;身元保証人,照会先
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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/06/08 18:42:52」(JST)

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A reference electrode is an electrode which has a stable and well-known electrode potential. The high stability of the electrode potential is usually reached by employing a redox system with constant (buffered or saturated) concentrations of each participants of the redox reaction.^[1]

There are many ways reference electrodes are used. The simplest is when the reference electrode is used as a half cell to build an electrochemical cell. This allows the potential of the other half cell to be determined. An accurate and practical method to measure an electrode's potential in isolation (absolute electrode potential) has yet to be developed.

Aqueous reference electrodes

Common reference electrodes and potential with respect to the standard hydrogen electrode:

Standard hydrogen electrode (SHE) (E=0.000 V) activity of H⁺=1
Normal hydrogen electrode (NHE) (E ≈ 0.000 V)concentration H⁺=1
Reversible hydrogen electrode (RHE) (E=0.000 V - 0.0591*pH)
Saturated calomel electrode (SCE) (E=+0.241 V saturated)
Copper-copper(II) sulfate electrode(CSE) (E=+0.314 V)
Silver chloride electrode (E=+0.197 V saturated)
pH-electrode (in case of pH buffered solutions, see buffer solution)
Palladium-hydrogen electrode
Dynamic hydrogen electrode (DHE)
Mercury-mercurous sulfate electrode (E=+0.64 V in sat'd K₂SO₄, E=+0.68 V in 0.5 M H₂SO₄) (MSE)

Standard Hydrogen Electrode
Cu-Cu(II) reference electrode
Ag-AgCl reference electrode

Nonaqueous reference electrodes

While it is convenient to compare between solvents to qualitatively compare systems it is not quantitatively meaningful. Much as pK_a are related between solvents, but not the same, so is the case with E°. While the SHE might seem to be a reasonable reference for nonaqueous work as it turns out the platinum is rapidly poisoned by many solvents including acetonitrile^{[citation needed]} causing uncontrolled drifts in potential. Both the SCE and saturated Ag/AgCl are aqueous electrodes based around saturated aqueous solution. While for short periods it may be possible to use such aqueous electrodes as references with nonaqueous solutions the long-term results are not trustworthy. Using aqueous electrodes introduces undefined, variable, and unmeasurable junction potentials to the cell in the form of a liquid-liquid junction as well as different ionic composition between the reference compartment and the rest of the cell.^[2] The best argument against using aqueous reference electrodes with nonaqueous systems, as mentioned earlier, is that potentials measured in different solvents are not directly comparable.^[3]

The potential for the Fc0/+ couple is sensitive to solvent.^[4]

	Fc^0/+ couple, NBu₄PF₆ at 298K
solvent	E
MeCN	0.40
CH2Cl2	0.46
THF	0.56
DMF	0.45
acetone	0.48

A Quasi-Reference Electrode (QRE) avoids the issues mentioned above. A QRE with ferrocene or similar internal standard (cobaltocene) referenced back to ferrocene is ideal for nonaqueous work. Since the early 1960s ferrocene has been gaining acceptance as the standard reference for nonaqueous work for a number of reasons, and in 1984, IUPAC recommended ferrocene (II/III) as a standard redox couple.^[5] The preparation of the QRE electrode is simple, allowing for a fresh reference to be prepared with each set of experiments. Since QREs are made fresh, there is also no concern with improper storage or maintenance of the electrode. QREs are also more affordable than other reference electrodes.

To make a quasi-reference electrode (QRE):^{[citation needed]}

Insert a piece of silver wire into concentrated HCl then allow the wire to dry on a lint-free cleaning cloth. This forms an insoluble layer of AgCl on the surface of the electrode and gives you an Ag/AgCl wire. Repeat dipping every few months or if the QRE starts to drift.
Obtain a Vycor glass frit (4 mm diameter) and glass tubing of similar diameter. Attach Vycor glass frit to the glass tubing with heat shrink Teflon tubing.
Rinse then fill the clean glass tube with supporting electrolyte solution and insert Ag/AgCl wire.
The ferrocene (II/III) couple should lie around 400 mV versus this Ag/AgCl QRE in an acetonitrile solution. This potential will varying up to 200 mV with the specific undefined conditions. Thus adding an internal standard such as ferrocene at some point during the experiment is always necessary.

Pseudo-reference electrodes

A pseudo-reference electrode is a term that is not well defined and borders on having multiple meanings since pseudo and quasi are often used interchangeably. They are a class of electrodes named pseudo-reference electrodes because they do not maintain a constant potential but vary predictably with conditions. If the conditions are known, the potential can be calculated and the electrode can be used as a reference. Most electrodes work over a limited range of conditions, such as pH or temperature, outside of this range the electrodes behavior becomes unpredictable. The advantage of a pseudo-reference electrode is that the resulting variation is factored into the system allowing researchers to accurately study systems over a wide range of conditions.

Yttria-stabilized zirconia (YSZ) membrane electrodes were developed with a variety of redox couples, e.g., Ni/NiO. Their potential depends on pH. When the pH value is known, these electrodes can be employed as a reference with notable applications at elevated temperatures.^[6]

References

^ Bard, Allen J.; Faulkner, Larry R. (2000-12-18). Electrochemical Methods: Fundamentals and Applications (2 ed.). Wiley. ISBN 0-471-04372-9.
^ Pavlishchuk, Vitaly V.; Anthony W. Addison (January 2000). "Conversion constants for redox potentials measured versus different reference electrodes in acetonitrile solutions at 25°C". Inorganica Chimica Acta 298 (1): 97–102. doi:10.1016/S0020-1693(99)00407-7. Retrieved 2009-04-17.
^ Geiger, William E. (2007-11-01). "Organometallic Electrochemistry: Origins, Development, and Future". Organometallics 26 (24): 5738–5765. doi:10.1021/om700558k. |accessdate= requires |url= (help)
^ Connelly, N. G., Geiger, W. E., "Chemical Redox Agents for Organometallic Chemistry", Chem. Rev. 1996, 96, 877.
^ Gritzner, G.; J. Kuta (1984). "Recommendations on reporting electrode potentials in nonaqueous solvents". Pure Appl. Chem. 56 (4): 461–466. doi:10.1351/pac198456040461. Retrieved 2009-04-17.
^ R.W. Bosch, D.Feron, and J.P. Celis, "Electrochemistry in Light Water Reactors", CRC Press, 2007.

External links

carbon graphene nanofiber junction reference electrode

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