EQCM Investigation on Electrodeposition and Charge Storage Behavior of Birnessite-Type MnO₂

Abstract

We have fabricated birnessite-type layered manganese oxide bycathodic reduction of aqueous permanganate ions (MnO4-) in thepresence of various alkaline metals. The electrodeposition andcharge storage processes were monitored by means ofelectrochemical quartz crystal microbalance (EQCM). Molarmasses acquired for the electrodeposition process revealed thatMnO2 grows concurrently with the incorporation of the coexistingcations and water molecules. The molar mass decreases in theorder of Li > Rb ~ K ~ Cs > Na, which is in good agreement withthe order of crystallinity. Clearly, the degree of crystallinity in theformation of birnessite depends on the incorporation amount of theguest ions and water. The birnessite-modified electrode increasesand decreases in mass during cathodic and anodic scans in Na2SO4electrolyte. The molar masses obtained were 21.6 and 24.9 g permole of electrons, respectively, both of which coincide with theatomic weight of Na (23.0 g).

Extending Electrochemical Quartz Crystal Microbalance Techniques to Macroscale Electrodes: Insights on Pseudocapacitance Mechanisms in MnOx-Coated Carbon Nanofoams

“…12,14,15,32,34 More recent EQCM reports examined MnOx pseudocapacitance phenomena and showed that cation insertion and ejection during reduction and oxidation, respectively, is the primary charge-compensation mechanism. 16,32,35 Traditional quartz crystal microbalance (QCM) experiments rely on the assumption that films are acoustically thin, thus allowing for gravimetric interpretation of the results using the Sauerbrey equation. Here, we first examine the EQCM behavior of electrodeposited Na-birnessite-type MnOx films, which we select as a thin-film mimic of the birnessite-MnOx coatings present in the carbon nanofoams.…”

“…Examination of Na-birnessite-type MnO 2 thin films.-Electrochemical quartz microbalance methods have been previously used to study MnOx, with most reports focused on analyzing the electrodeposition process of MnOx thin films. 12,14,15,32,34 More recent EQCM reports examined MnOx pseudocapacitance phenomena and showed that cation insertion and ejection during reduction and oxidation, respectively, is the primary charge-compensation mechanism. 16,32,35 Traditional quartz crystal microbalance (QCM) experiments rely on the assumption that films are acoustically thin, thus allowing for gravimetric interpretation of the results using the Sauerbrey equation.…”

“…32 Briefly, electrodeposition was performed in 2 mM KMnO 4 containing 50 mM NaCl by applying 0 V vs. Ag/AgCl, until a deposition charge density of 140 mC cm -2 was achieved. Mass changes for thin-film experiments were calculated according to the Sauerbrey equation 33 using a calibration factor of 232 Hz cm 2 μg -1 , determined separately via Cu deposition experiments.…”

“…All electrochemical experiments were performed using a Reference 600 potentiostat and eQCM 10M electrochemical quartz crystal Films of birnessite-type MnOx were prepared using a previously published procedure. 32 Briefly, electrodeposition was performed in 2 mM KMnO 4 containing 50 mM NaCl by applying 0 V vs. Ag/AgCl, until a deposition charge density of 140 mC cm -2 was achieved. Mass changes for thin-film experiments were calculated according to the Sauerbrey equation 33 using a calibration factor of 232 Hz cm 2 μg -1 , determined separately via Cu deposition experiments.…”

Vacuum Filtration‐and‐Transfer Technique Helps Electrochemical Quartz Crystal Microbalance to Reveal Accurate Charge Storage in Supercapacitors

“…To construct better SCs, it is of great importance to understand the charge storage mechanisms of these materials at molecular level. Recently, electrochemical quartz crystal microbalance (EQCM) as an in situ experimental methodology has started to address the charge storage mechanisms of SCs, thanks to its super‐sensitive change in the gravimetry (10 −9 g) and thickness during charging and discharging process …”