X-ray Photoelectron Spectroscopy and in Situ X-ray Absorption Spectroscopy Studies on Reversible Insertion/Desertion of Dicyanamide Anions into/from Manganese Oxide in Ionic Liquid

Abstract

Pseudocapacitive characteristics of manganese (Mn) oxide were recognized in aprotic ionic liquid (IL), namely, butylmethylpyrrolidinium−dicyanamide (BMP−DCA), within a potential window of 3 V. The electrochemical energy storage mechanism was examined using X-ray photoelectron spectroscopy and in situ X-ray absorption spectroscopy. It was confirmed that the DCA− anions, instead of the bigger BMP+ cations, were the working species that compensate the Mn valent state variation upon charging and discharging in the IL electrolyte. During oxidation of the Mn oxide electrode, to keep the charges balanced, the quasi-linear DCA− anions were inserted into the tunnels between the MnO6 octahedral units, expanding the structural framework. Importantly, a highly reversible process was observed during the subsequent reduction step. XPS depth profiling analyses showed that the electrochemical reaction thickness was approximately 50 nm.

Nanostructured MnO2 for Electrochemical Capacitor

“…This behavior suggests that faradic phenomena occur during the charge-storage mechanism. The presence of redox waves during the charge/discharge process was already reported for several MnO 2 -based electrodes (Hu & Tsou, 2002;Brousse et al, 2006;Ghodbane & Favier 2009;Chang et al, 2009;Lee et al, 2010). The electrochemical experiments in their work demonstrate that the crystallographic form of MnO 2 influences the electrochemical performance, and the small tunnel of -MnO 2 was not suitable to store cations, while the large tunnel size of -MnO 2 favors the storage of cations Cheng et al, 2010).…”

“…In addition, the presence of other metal cations in the tunnel in advance hinders the diffusion and storage of the electrolyte cations leading to a decrease in capacitance. More recently, further research on the tunnel storage of MnO 2 even revealed that the aprotic ionic liquids anions with the far bigger diameters than that of alkaline metal ion, could also be stored in the tunnels of MnO 2 (Xu et al 2010 ;Chang et al, 2009;Lee et al, 2010). More recently, a multivalent cation storage mechanism was proposed by Xu et al, they think not only univalent alkaline metal cations could store in the tunnels of MnO 2 , bivalent alkaline-earth metal cations also are present in it .…”

Ionic Liquid for High Voltage Supercapacitor

“…And their cycle-ability was not enough to actual application. Aprotic ILs were tried as electrolyte for pseudoelectrode in some cases [66]. The pseudomaterial was manganese dioxide (MnO 2 ), and the IL was …”

Electrode–Electrolyte Interfacial Processes in Ionic Liquids and Sensor Applications

“…And the electroreflectance spectroscopies [47] have provided information about the orientation of molecules in adsorbed overlayers. X-ray absorption spectroscopies [48,49] were employed to determine the coordination numbers of adsorbed species and the substrate-adsorbate and adsorbate-adsorbate bond lengths. Ab initio-based computations on the property of electrode materials and continuum modeling have been incorporated to provide theoretical insights and predictions [50,51].…”