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

Abstract

In this study, porous manganese oxide (MnOx) 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 Mn3O4 to the conducting layered birnessite MnO2. 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 MnOx/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 MnOx-MEs is attributed to the pseudocapacitive MnOx as well as the three-dimensional architectural framework provided by the carbon micro-pillars.

On-Chip Asymmetric Microsupercapacitors Combining Reduced Graphene Oxide and Manganese Oxide for High Energy-Power Tradeoff

“…The stack capacitance, energy and power densities were calculated by normalizing the C areal , ED areal and PD areal with the rGO or MnO x thickness, depending upon the higher thickness. The areal energy-power trade-off between all the MSC devices constructed in this work has been depicted in a Ragone chart ( Figure S3 ); the asymmetric rGO//MnO x -0.9C MSC was able to deliver an energy density of 0.274 μWh·cm −2 at a power density of 193.6 μW·cm −2 (pertaining to a capacitance of 1.63 mF·cm −2 ) which is higher than other reports documenting on-chip MnO x -based systems [ 32 , 35 ] but lower than reports on carbon onions and conjugated polymers [ 45 , 46 ]. A comparative Ragone chart depicting the stack energy and power densities of the asymmetric rGO//MnO x -0.9C MSC along with other commercial EES [ 45 ] as well as other MSC systems reported in the literature is shown in Figure 8 .…”

“… Ragone plot depicting the volumetric energy and power densities exhibited by the asymmetric rGO//MnO x -0.9C MSC in comparison with thin film lithium ion battery, commercial supercapacitors and electrolytic capacitors along with carbon onion-based microsupercapacitors (produced with permission from Reference [ 45 ]) and other data points taken from the Reference [ 32 , 47 , 48 , 49 ]. …”

“…As pseudocapacitive or redox materials, manganese oxides (MnO x ), in all polymorphs, have been widely studied owing to their high theoretical specific capacitance, environmental benignity, large abundance and low cost [ 29 , 30 , 31 , 32 ]. Different asymmetric configurations utilizing MnO x have been investigated for MSC applications including activated carbons (AC) [ 33 ], carbon nanotubes (CNT) [ 34 ], laser scribed graphene (LSG) [ 35 ], as well as graphene quantum dot (GQD) [ 36 ] counter electrodes.…”

Electrostatically Sprayed Reduced Graphene Oxide-Carbon Nanotubes Electrodes for Lithium-Ion Capacitors

“…Schematic illustration and a practical image of the ESD process are presented in Figure 1. ESD offers a rapid and simple electrode fabrication approach [21,22]. GO precursor solution and ESD process parameters can be easily controlled in order to obtain numerous morphologies that may influence the electrochemical properties of the graphene-based electrode.…”

Poly (Ionic Liquid) Based Electrolyte for Lithium Battery Application

“…This technique operates without vacuum which makes the method less costly compared to other thin film deposition techniques such as. Chemical vapor deposition (CVD), electrophoretic deposition (EPD) and layer-by-layer (LBL) deposition technique [77]. Electrodes prepared with this technique does not need any polymeric binders thus lowers resistance and dead weight to the electrode [78].…”