Electrochemical performance and structural evolution of spray pyrolyzed Mn 3 O 4 thin films in different aqueous electrolytes: effect of anions and cations.

This work presents the impact of cycling in different cationic and anionic aqueous electrolytes on the electrochemical storage performance of the Mn 3 O 4 thin film electrode prepared using the chemical pyrolysis method. Studies on the as-deposited electrode confirmed the formation of Mn 3 O 4 phase. Extensive electrochemical analysis was performed using Na 2 SO 4 , NaCl, Li 2 SO 4 , K 2 SO 4 , and MgSO 4 electrolytes to examine the influence of cations and anions on charge storage behaviour. Considerable changes were observed in the specific capacitances owing to different ionic sizes as well as hydrated ionic radius of the electrolyte ions. Accordingly, the electrode unveiled a good performance showing a specific capacitance of around 187 F g -1 at 0.5 A g -1 in K 2 SO 4 electrolyte. Further, the electrode properties are examined after 500 CV cycles to trace the changes in the structural and morphological properties. X-ray diffraction (XRD) and Raman spectroscopic studies illustrate a partial phase transformation of electrodes from Mn 3 O 4 to MnO 2 irrespective of the electrolytes. These results are further corroborated with X-ray photoelectron spectroscopic (XPS) analysis where there was an increment in the oxidation state of manganese. It has been observed that the surface properties were significantly changed with cycling, as manifested by the wettability studies of the electrodes. The obtained results brings out the significance of electrolyte ions on the charge storage characteristics of Mn 3 O 4 thin film electrodes in light of their possible application in electrochemical capacitors.