XRD/Raman spectroscopy studies of the mechanism of (de)intercalation of Na⁺ from/into highly crystalline birnessite

Abstract

Due to its low-cost and environmental friendliness, birnessite-type manganese oxide has attracted wide interest for use as a cathode material in electrochemical energy storage applications.

Light-Mediated Electrochemical Synthesis of Manganese Oxide Enhances Its Stability for Water Oxidation

“…This peak is not observed for MnO x films grown in the dark. A peak between 606 and 611 cm –1 is occasionally observed in birnessite films, ,,,, but this peak is typically left unassigned. Along with the peak at 651 cm –1 , Scheitenberger and coworkers also assigned this peak to vibrations of interlayer H 2 O in birnessite .…”

Structural Evolution of Air-Exposed Layered Oxide Cathodes for Sodium-Ion Batteries: An Example of Ni-doped NaxMnO2

“…The spectrum of the active material (NMNO_B) is dominated by the very intense band at 635 cm –1 . The band originates from the A 1g symmetric (Mn/Ni)–O stretching vibration of (Mn/Ni)­O 6 octahedra along the c -axis (υ 1 ). − Other bands associated with the (Mn/Ni)–O vibrations and having lower intensity are detected at lower frequencies. They arise from the (Mn/Ni)–O stretching vibration in the basal plane of [(Mn/Ni)­O 6 ] sheets at 580 cm –1 (υ 2 ), and from the E g (Mn/Ni)–O vibration of birnessite structure at 493 cm –1 (υ 3 ). , The very weak contributions at ∼360 cm –1 (υ 4 ) and ∼280 cm –1 (υ 5 ) are ascribed to the asymmetric stretching vibration of the Na + ions. , …”

“…They arise from the (Mn/Ni)−O stretching vibration in the basal plane of [(Mn/Ni)O 6 ] sheets at 580 cm −1 (υ 2 ), and from the E g (Mn/Ni)−O vibration of birnessite structure at 493 cm −1 (υ 3 ). 64,66 The very weak contributions at ∼360 cm −1 (υ 4 ) and ∼280 cm −1 (υ 5 ) are ascribed to the asymmetric stretching vibration of the Na + ions. 64,66 The lower frequency region of the spectra of the pristine and cycled electrodes does not significantly differ from the spectrum of the active material, confirming the preservation of the birnessite structure.…”

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

“…EIS characterization is typically performed at the measured open‐circuit potential of the working electrode, as this value corresponds to equilibrium between oxidation and reduction reactions of electrolyte species at the electrode surface, where the Butler‐Volmer equation for redox processes is approximately linear [85] . However, open‐circuit potential measurements recorded prior to every CV experiment reveal that this equilibrium scenario did not occur at a consistent potential value over the course of electrochemical testing: open‐circuit potential values in the range 0.21–0.76 V vs Ag|AgCl (3 M KCl) were exhibited by the four electrodes, possibly due to cyclical variations in the average Mn oxidation state and the changing concentrations of intercalated Na + and K + ions [30,86] . To overcome this difficulty, EIS was instead conducted at two widely separated bias potentials within the electrochemical stability window, 0.0 V and 0.5 V vs Ag|AgCl (3 M KCl), thereby enabling impedance behaviors of each system to be assessed as a function of the applied potential.…”

“…[85] However, open-circuit potential measurements recorded prior to every CV experiment reveal that this equilibrium scenario did not occur at a consistent potential value over the course of electrochemical testing: open-circuit potential values in the range 0.21-0.76 V vs Ag j AgCl (3 M KCl) were exhibited by the four electrodes, possibly due to cyclical variations in the average Mn oxidation state and the changing concentrations of intercalated Na + and K + ions. [30,86] To overcome this difficulty, EIS was instead conducted at two widely separated bias potentials within the electrochemical stability window, 0.0 V and 0.5 V vs Ag j AgCl (3 M KCl), thereby enabling impedance behaviors of each system to be assessed as a function of the applied potential. Indeed, it has been acknowledged elsewhere that since the equivalent circuit components of supercapacitor systems are commonly voltagedependent, the practice of conducting EIS exclusively at the open-circuit potential is liable to restrict the information that can be gleaned from the technique.…”