Electrostatic Spray Deposition-Based Manganese Oxide Films—From Pseudocapacitive Charge Storage Materials to Three-Dimensional Microelectrode Integrands

摘要

In this study, porous manganese oxide (MnO x ) thin films were synthesized via electrostatic spray deposition (ESD) and evaluated as pseudocapacitive electrode materials in neutral aqueous media. Very interestingly, the gravimetric specific capacitance of the ESD-based electrodes underwent a marked enhancement upon electrochemical cycling, from 72 F?g ?1 to 225 F?g ?1 , with a concomitant improvement in kinetics and conductivity. The change in capacitance and resistivity is attributed to a partial electrochemical phase transformation from the spinel-type hausmannite Mn 3 O 4 to the conducting layered birnessite MnO 2 . Furthermore, the films were able to retain 88.4% of the maximal capacitance after 1000 cycles. Upon verifying the viability of the manganese oxide films for pseudocapacitive applications, the thin films were integrated onto carbon micro-pillars created via carbon microelectromechanical systems (C-MEMS) for examining their application as potential microelectrode candidates. In a symmetric two-electrode cell setup, the MnO x /C-MEMS microelectrodes were able to deliver specific capacitances as high as 0.055 F?cm ?2 and stack capacitances as high as 7.4 F·cm ?3 , with maximal stack energy and power densities of 0.51 mWh·cm ?3 and 28.3 mW·cm ?3 , respectively. The excellent areal capacitance of the MnO x -MEs is attributed to the pseudocapacitive MnO x as well as the three-dimensional architectural framework provided by the carbon micro-pillars.