Sodium Charge Storage in Thin Films of MnO2 Derived by Electrochemical Oxidation of MnO Atomic Layer Deposition Films. Issue 14 (21st October 2015)

• Record Type: Journal Article
• Authors: Young, Matthias J.; Neuber, Markus; Cavanagh, Andrew C.; Sun, Huaxing; Musgrave, Charles B.; George, Steven M.
• Is Part Of: Journal of the Electrochemical Society. Volume 162:Issue 14(2015)
• Page Start: A2753
• Page End: A2761
• Publication Date: 2015-10-21
• Subjects: Atomic Layer Deposition -- Cyclic Voltammetry -- Electrochemical QCM -- Manganese Oxide -- Pseudocapacitor -- Sodium -- Thin Film; Electrochemistry -- Periodicals; 541.3705
• DOI: 10.1149/2.0671514jes
• Languages: English
• ISSNs: 0013-4651

Abstract

Abstract : Sodium charge storage in ultrathin MnO2 films was studied using cyclic voltammetry (CV) and electrochemical quartz crystal microbalance (EQCM) measurements. The MnO2 films were fabricated by electrochemical oxidation of MnO films grown by atomic layer deposition (ALD). CV analysis confirmed that oxidation of MnO to MnO2 involved two moles of electrons per mole of Mn in the MnO ALD film. Scanning electron microscopy (SEM) images revealed that electrochemical oxidation of MnO led to the formation of MnO2 nanosheets. EQCM measurements suggested that Na + cations participate in charge storage in MnO2 . X-ray photoelectron spectroscopy (XPS) experiments measured sodium in MnO2 after both positive/anodic and negative/cathodic voltage sweeps. The stoichiometry was Na0.25 MnO2 after negative/cathodic voltage sweeps. Approximately one-half of the sodium was removed after positive/anodic voltage sweeps. The areal capacitance increased progressively with initial MnO ALD film thickness. This increase in areal capacitance is consistent with bulk charge storage in MnO2 or higher surface area of MnO2 nanosheets resulting from larger MnO ALD film thicknesses. Experiments at varying scan rates indicated that charge storage in MnO2 originates from a combination of capacitive and diffusive processes. Bulk charge storage makes a significant contribution to total charge storage in the thicker MnO2 films.