Using pH Indicator To Demonstrate Supercapacitor Reactions

Abstract

In this supplement to our second-year supercapacitor lab (Bringing Real-World Energy-Storage Research into a Second-Year Physical-Chemistry Lab Using a MnO 2 -Based Supercapacitor. J. Chem. Educ. 2018, 95 (11), 2028− 2033), we incorporate a color indicator as indirect evidence for the manganese oxide's pseudocapacitive reaction (MnO 2 + H + + e − ⇌ MnOOH). Using the evidence of pH changes (the methyl red goes from light yellow to red during an oxidative potential hold), students can make the link between oxidation state changes and the applied potential of the electrochemical experiment. Herein, we optimize the indicator concentration and electrochemical parameters to ensure the color changes are evident. Optimal responses arise when 15 μM methyl red is coupled with a 2 min, 0.8 V potentiostatic hold.