an electrochemistry question

angela2007

Mn2+ + 2 H2O - MnO2 + 4 H+ + 2 e− ( −1.22 V), this reaction is acucurate. the standard potential is negative, then why all the work for the formation of MnO2 need to be done in anodic potential?

symbolipoint

According to what you wrote for the reaction (interpreting for one wrong "-" symbol, needs to be an arrow), the half-reaction is an oxidation and requires energy in order to occur. The negative half-reaction potential tells you that the half reaction is not spontaneous and so requires energy to be supplied.

angela2007

my question is in three electrode system: working electrode, Pt counter electrode, and Ag/AgCl reference electrode.
for example, Mn2+ + 2 H2O -MnO2 + 4 H+ + 2 e− ( −1.22 V), the deposition of Mno2 will be accomplished on postive potential. Cr3+ +3e- Cr ( −0.74 V), the depsotion of metallic Cr will be accomplished on negative potential.
I Know for both the half-reactions, they are non-spontaneous and need external electric energy. My point is why the deposition of Mno2 is not done in negative potential range.