Why Does MnO2 Deposit at Positive Potentials in a Three-Electrode System?

[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 positive 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 since E is equal to -1.22 V.

I cannot put the arrow in the reaction. please ingore that.

Thank you!

 

[chemisttree]

Are you asking what the difference is between plating out a conductive metal vs. a metallic oxide?