Probing the Charge Storage Mechanism of a Pseudocapacitive MnO₂ Electrode Using in Operando Raman Spectroscopy

Abstract

While manganese oxide (MnO2) has been extensively studied as an electrode material for pseudocapacitors, a clear understanding of its charge storage mechanism is still lacking. Here we report our findings in probing the structural changes of a thin-film model MnO2 electrode during cycling using in operando Raman spectroscopy. The spectral features (e.g., band position, intensity, and width) are correlated quantitatively with the size (Li+, Na+, and K+) of cations in different electrolytes and with the degree of discharge to gain better understanding of the cation-incorporation mechanism into the interlayers of pseudocapacitive MnO2. Also, theoretical calculations of phonon energy associated with the models of interlayer cation-incorporated MnO2 agree with the experimental observations of cation-size effect on the positions of Raman bands. Furthermore, the cation-size effects on spectral features at different potentials of MnO2 electrode are correlated quantitatively with the amount of charge stored in the MnO2 electrode. The understanding of the structural changes associated with charge storage gained from Raman spectroscopy provides valuable insights into the cation-size effects on the electrochemical performances of the MnO2 electrode.

Nickel Confined in the Interlayer Region of Birnessite: an Active Electrocatalyst for Water Oxidation

“…[21][22][23] Figure S4 shows that both birnessite and birnessite exposed to hydrazine exhibited similar Raman spectra. [21][22][23] Figure S4 shows that both birnessite and birnessite exposed to hydrazine exhibited similar Raman spectra.…”

Langmuir–Blodgett Nanowire Devices for In Situ Probing of Zinc‐Ion Batteries

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Metal Oxide and Hydroxide–Based Aqueous Supercapacitors: From Charge Storage Mechanisms and Functional Electrode Engineering to Need‐Tailored Devices

“…In situ nanoindentation revealed softening of MnO 2 by proton intercalation, due to reduction of the elastic modulus and hardness of MnO 2 after discharging, in agreement with particle expansion. [23] Copyright 2015, American Chemical Society. Thus, it is worth stating that MnO x -based electrodes with porous Adv.…”

“…[23] In the high charge state of MnO 2 , water molecules intercalated in the tunnels/interlayer, resulting in structural similarity in aqueous electrolytes with different cations. [23] In the high charge state of MnO 2 , water molecules intercalated in the tunnels/interlayer, resulting in structural similarity in aqueous electrolytes with different cations.…”