Electrodeposition of manganese oxide from eutectic urea/choline chloride ionic liquid: An in situ study based on soft X-ray spectromicroscopy and visible reflectivity

In this work, we describe a novel approach to the fabrication of MnO2, consisting in Mn electrodeposition from a choline chloride/urea eutectic ionic liquid bath followed by controlled electrochemical oxidation in an aqueous solution. Both electrodeposition and electro-oxidation processes have been studied by electrochemical and in situ spectroelectrochemical approaches. Synchrotron-based soft X-ray scanning microscopy and absorption spectroscopy were used to measure in situ the Mn valence distribution on the electrodes and within the cell. The oxidation process was followed in situ by visible reflectivity measurements: the different stages of the oxidation process could be discriminated dynamically on the basis of relative reflectivity changes. The capacitance of the electrochemically fabricated films has been measured with cyclic voltammetry and electrochemical impedance spectrometry.

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► MnO2 nanowires were grown by Mn electrodeposition followed by controlled oxidation.
► Electrodeposition from eutectic ionic liquid was followed by X-ray microspectroscopy.
► Combined STXM and space resolved XAS yield chemical state distribution in situ.
► Controlled oxidation of Mn to MnO2 was monitored in situ by VIS electroreflectance.
► MnO2 nanowire films grown from Mn electrodeposits exhibit capacitance of 70 mF cm−2.