Polypyrrole Modified Graphite Electrode for Supercapacitor Application: The Effect of Cycling Electrolytes

Abstract

Graphite electrode was modified by polypyrrole (PPy) thin film. PPy was electrodeposited potentiostatically by applying -1.5 V from acidic aqueous solution having pyrrole monomers. The waiting time of deposition solution effect the surface coverage of resulted films. PPy modified electrodes fabricated by old solution have lower surface coverage than PPy obtained from freshly prepared solution. PPy films were transferred to aqueous (acidic, neutral, alkaline) and a non-aqueous (Deep Eutectic Solvent) solutions for cycling. Capacitance performance of PPy film in a choline chloride based ionic liquid (Ethaline) was compared with that of PPy films in aqueous solutions. As PPy film in salt solution (LiClO4 and NaCl) was evolved because deposition electrolyte was different (H2SO4) than deposition electrolyte and salt ions are exchanged at the beginning of cycling. Film obtained in acidic media was transferred into alkaline solution or ionic liquid is electroinactive. PPy film is strongly electroactive in an acidic media for hundreds of cycles as acidic media can cause the highest charge which is directly related to capacitive performance. Upon increasing pH value of cycling electrolyte, current and charge value decreases. PPy film in a salt solution (NaCl or LiClO4 in water) and acidic solution (H2SO4) is electroactive and can be used for supercapacitor application. As PPy film in ionic liquids and alkaline solution cannot be electroactive, they cannot be used for supercapacitor applications. Capacity retention of PPy in KOH and Ethaline is low (around 5%). However, PPy thin film in H2SO4 has 77% of capacitance retention after 500 scans.