Scalable Synthesis of Pre‐Intercalated Manganese(III/IV) Oxide Nanostructures for Supercapacitor Electrodes: Electrochemical Comparison of Birnessite and Cryptomelane Products

Abstract

Manganese(III/IV) oxide is a promising pseudocapacitive material for supercapacitor electrodes due to favorable attributes such as its chemical resilience, high earth abundance and low specific cost. Herein, the morphological, compositional and electrochemical characteristics of co‐precipitated manganese(III/IV) oxide products, each described by the general formula NaxKyMnOz, are investigated to establish how these properties are influenced by synthesis conditions. NaxKyMnOz growths in low‐temperature (<100 °C) basic and acidic environments are shown to promote the formation of turbostratic birnessite and cryptomelane phases, respectively, with the latter polymorph containing a relatively low concentration of interstitial Na+ and K+ cations. It is demonstrated that K+ pre‐insertion during synthesis yields lower initial charge‐transfer resistances than equivalent Na+ intercalation, and that this parameter correlates strongly with storage performance. Accordingly, Na‐mediated storage initially delivers inferior specific capacitances and Coulombic efficiencies than K‐based mechanisms, but K+ intercalation/deintercalation causes faster capacitance decay during prolonged galvanostatic cycling. Furthermore, whilst crystallographic phase is shown to have a weaker effect on NaxKyMnOz storage properties than the choice of intercalating guest cations, cryptomelane electrodes are more susceptible to cycling‐induced capacitance and efficiency losses than their birnessite counterparts. In combination, these insights provide an instructive foundation for the optimization of NaxKyMnOz in high‐power storage applications.

Efficient Electrochemical Performance of Sr(OH)2:MnO2 Binary Composites for Solid State Symmetric Supercapacitor

“…The low value of Rs leads to the better electrochemical performance, i. e., it is related to the conductivity of the electrode. [81][82][83][84][85] The obtained components of the circuit like Rs, R CT , Z W and Q have already been articulated in the frequency-dependent plot (Nyquist graph) of the three-electrode measurements. In the highfrequency zone, the absence of the apparent semicircle assured the small charge transfer resistance R CT for the fabricated device.…”

“…The first part, Rs, comprises the resistance that arises between collector current and the active electrode, as well as the solution resistance of the electrode itself. The low value of Rs leads to the better electrochemical performance, i. e., it is related to the conductivity of the electrode [81–85] . The obtained components of the circuit like Rs, R CT , Z W and $${Q}$$ have already been articulated in the frequency‐dependent plot (Nyquist graph) of the three‐electrode measurements.…”

Engineering and Applied Sciences

“…This is attributed to the incorporation of K+ cations into the MnO2 structure by heat treatment, which enhances the ion insertion/extraction capacity of the material. At fast rates the capacitance tends to stabilize at one value, indicating pseudocapacitive behavior (Jones et al, 2023). It has been shown that the addition of ions makes the charge storage mechanisms more surface redox dominated and can improve the specific capacitance (Barclay et al, 2023).…”

Test of electrodes based on manganese oxide with and without potassium cations for supercapacitors

“…This is attributed to the incorporation of K+ cations into the MnO2 structure by heat treatment, which enhances the ion insertion/extraction capacity of the material. At fast rates the capacitance tends to stabilize at one value, indicating pseudocapacitive behavior (Jones et al, 2023). It has been shown that the addition of ions makes the charge storage mechanisms more surface redox dominated and can improve the specific capacitance (Barclay et al, 2023).…”