According to Nernst equation, i obtained the m/n ( proton number/electron number) ratio of1:2, According to Bard equation, electron number is 2, proton number is 1. According to theoretical calculation, in combination with Electrochemical reduction mechanism, electron number is 2, proton number is 2, theoretical calculation result is different with experimental calculation results, why the number of protons is different? could it be influenced by other factors like pH effect or electrode modified materials ?
Dear Ahmed S Abo Dena
Thank you very much for your reply .
My analyte is Methylglyoxal (MG) , is there a pka?
1.Electrochemical reduction path of MG and its hydrated form, MGH see equationth
2.The number of protons was calculated by Nernst equationth, Ep changed linearly with the pH (Fig. 3C), the slope of dEpa/dpH plots was -0.029, so the m/n ratio of MG was about 1:2.
According to Bard and Faulkner, α can be given as follows（equationt see equationth）, Where Ep is the peak potential (0.879 mV), and Ep/2 is the half-wave potential (0.815 mV) that is the potential at which the current is half the peak value, αn is 0.75, generally, the value of α is between 0.3 and 0.7, So, from this we got the value of α to be 0.38. Further, the number of n in the electroreduction of MG was calculated to be 2. Thus, it may assume that the electrode reaction of MG was accompanied by 1 proton and 2 electrons.
Your "Nernst" equation is not correct. The correct one for m=n=1 is
Eapp= Eo + (60 mV)×log((1+ K [H+])/(1+ K'[H+])),
where K and K' are dissociation constants for the reduce and oxidized forms. To understand the process you must construct the Pourbaix diagram.
Dear Prof. Yurii V Geletii
Thank you very much for pointing out our problems firstly. I see a lot of papers for electrochemical sensors,
They all use this equation to calculate the number of protons, I'm not good at this. Can you explain it more detail?
Dear Prof. Sylvie Delpech
How do you reach One proton and One electron. I've read papers pKa for the effect of proton number. Is there a pka for Methylglyoxal (MG)? Do you know whihc factors for the effect of proton number? is it possible that it is the enediol-keto equilibrium or direct reduction for keto form?
even other ?
Yangping Wen
This is too complex problem to explain it briefly. Read reviews on PCET, square scheme, etc.
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