A reversible hydrogen electrode (RHE) is a reference electrode, more specifically a subtype of the standard hydrogen electrodes, for electrochemical processes. Unlike the standard hydrogen electrode, its measured potential does change with the pH, so it can be directly used in the electrolyte.[1][2][3]
The name refers to the fact that the electrode is directly immersed in the actual electrolyte solution and not separated by a salt bridge. The hydrogen ion concentration is therefore not 1 mol/L, or 1 mol/kg, but corresponds to that of the electrolyte solution. In this way, it is possible to achieve a stable potential with a changing pH value. The potential of the RHE correlates to the pH value:
In general, for a hydrogen electrode in which the reduction of the hydronium ions (H3O+) occurs:
or, more often commonly written simply with H+ denoting H3O+:
with,
the equilibrium potential E depends on the hydrogen pressure pH2 and the activity aH+ as follows:
Here, is the standard reduction potential (by convention equal to zero), R is the universal gas constant, T the absolute temperature, and F is the Faraday constant.
An overpotential occurs in the electrolysis of water. This means that the required cell voltage is higher than the equilibrium potential because of kinetic limitations. The potential increases with increasing current density at the electrodes. The measurement of equilibrium potentials is therefore possible without power.
Principle
[edit]The reversible hydrogen electrode is a fairly practical and reproducible electrode "standard". The term refers to a hydrogen electrode immersed in the electrolyte solution actually used.
The benefit of that electrode is that no salt bridge is needed:
- There is no contamination of the electrolyte by chlorides or sulfates.
- There are no diffusion potentials at the electrolyte bridge (liquid junction potential). This is important at temperature different to 25 °C.
- Long-time measurements are possible (no electrolyte bridge means no maintenance of the bridge)
See also
[edit]References
[edit]- ^ Cai, Yu; Anderson, Alfred B. (2004). "The reversible hydrogen electrode: potential-dependent activation energies over platinum from quantum theory". The Journal of Physical Chemistry B. 108 (28): 9829. doi:10.1021/jp037126d.
- ^ Staehler, M.; Wipperman, K. & Stolten, D. "Instabilities of the reversible hydrogen reference electrode in direct methanol fuel cells" (PDF). 2004 Joint International Meeting of the Electrochemical Society, Abstract 1863.
- ^ MacInnes, Duncan A. & Adler, Leon (1919). "Hydrogen overvoltage". Proceedings of the National Academy of Sciences of the United States of America. 5 (5): 160–3. Bibcode:1919PNAS....5..160M. doi:10.1073/pnas.5.5.160. JSTOR 84265. PMC 1091559. PMID 16576366.
Well, that’s interesting to know that Psilotum nudum are known as whisk ferns. Psilotum nudum is the commoner species of the two. While the P. flaccidum is a rare species and is found in the tropical islands. Both the species are usually epiphytic in habit and grow upon tree ferns. These species may also be terrestrial and grow in humus or in the crevices of the rocks.
View the detailed Guide of Psilotum nudum: Detailed Study Of Psilotum Nudum (Whisk Fern), Classification, Anatomy, Reproduction