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

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The discussion centers on the electrochemical deposition of MnO2 in a three-electrode system comprising a working electrode, a Pt counter electrode, and an Ag/AgCl reference electrode. It highlights that the deposition of MnO2 occurs at positive potentials, specifically at -1.22 V, while the deposition of metallic Cr occurs at negative potentials (-0.74 V). The participants clarify that both half-reactions are non-spontaneous and require external electric energy, raising questions about the differing potential ranges for deposition of conductive metals versus metallic oxides.

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angela2007
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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!
 
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Are you asking what the difference is between plating out a conductive metal vs. a metallic oxide?
 

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