Compared with the acidic electrolyte where H+ is converted to H, it is likely that the conversion of H2O into H is more sluggish, so the activity of HER in acid is usually higher than that in alkaline. But how about the comparison within basic electrolyte,i.e., increasing the concentration of OH- in electrolyte usually leads to a higher HER activity? Why? Is there any qualitative explanation besides that PH can influence the Hydrogen binding energy?
Thx
To remove 1 hydrogen from water molecules is easier from OH-. We need to increase the energy, in this case potential. Water molecule is polar, so one electron cloud is weak in one side.
Water reduction is a half reaction of water splitting to H2 and O2. The reaction thermodynamics of water reduction is described by a simple formula:
E = 0.059*pH (V).
The reaction rate is not controlled exclusively by thermodynamics but also by activation barrier (kinetics) The activation barrier can be lowed by the catalyst. The catalyst activity depends on pH.
In addition, water oxidation might be a rate limiting step for the overall water splitting. Water oxidation is more favorable under basic conditions.
The addition of OH- scavenge H+ released during electrochemical measurement. That way we add buffer
Is more difficult to remove H+ from OH- compared to H+ from H2O
why?
First the negative electron cloud from OH- cause the repulsion of electrons flow from current
Second, the Hydrogen is stronger attracted to oxygen (electrongativity), so quite difficult to release H+
But in water molecules H+ need less energy to be released
In addition, the size and distribution of water (and chiral hydration) nano-clusters depend on the pH[1,2] (and the temperature).
1. https://www.researchgate.net/publication/295863849_The_Clusters-in-a-Liquid_Approach_for_Solvation_New_Insights_from_the_Conformer_Specific_Gas_Phase_Spectroscopy_and_Vibrational_Optical_Activity_Spectroscopy
2. Vibrational spectral signature of the proton defect in the three-dimensional H+(H2O)21 cluster http://science.sciencemag.org/content/344/6187/1009?cited-by=yes&legid=sci;344/6187/1009
Article The Clusters-in-a-Liquid Approach for Solvation: New Insight...
Dear Antonio,
It's really funny to read your comments. Really revolutionary thoughts. Please, continue.
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