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Chemistry. 2014 Apr 7;20(15):4194-211. doi: 10.1002/chem.201302473. Epub 2014 Mar 11.

The protoelectric potential map (PPM): an absolute two-dimensional chemical potential scale for a global understanding of chemistry.

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Institut für Anorganische und Analytische Chemie der Uni Freiburg, Albertstr. 21,79104 Freiburg (Germany), Fax: (+49) 761-203-6001; Freiburger Materialforschungszentrum FMF, Stefan-Meier Str. 21, 79104 Freiburg (Germany).


We introduce the protoelectric potential map (PPM) as a novel, two-dimensional plot of the absolute reduction potential (peabs scale) combined with the absolute protochemical potential (Brønsted acidity: pHabs scale). The validity of this thermodynamically derived PPM is solvent-independent due to the scale zero points, which were chosen as the ideal electron gas and the ideal proton gas at standard conditions. To tie a chemical environment to these reference states, the standard Gibbs energies for the transfer of the gaseous electrons/protons to the medium are needed as anchor points. Thereby, the thermodynamics of any redox, acid-base or combined system in any medium can be related to any other, resulting in a predictability of reactions even over different media or phase boundaries. Instruction is given on how to construct the PPM from the anchor points derived and tabulated with this work. Since efforts to establish "absolute" reduction potential scales and also "absolute" pH scales already exist, a short review in this field is given and brought into relation to the PPM. Some comments on the electrochemical validation and realization conclude this concept article.


Gibbs solvation energy; absolute acidity; absolute redox potential; electrochemistry; thermodynamics


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