A comparison of protic and aprotic ionic liquids as effective activating agents of kraft lignin. Developing functional MnO2/lignin hybrid materials

摘要

Protic and aprotic ionic liquids (1-butylimidazolium hydrogen sulfate(VI) and 1-butyl-3-methylimidazolium methyl sulfate(VI)) were investigated for the first time as potential activators of lignin. The activation process was expected to increase the content of carbonyl groups, which have the capacity to transport protons and electrons in electrochemical applications. Fourier transform infrared (FTIR) spectra showed that activation with the protic ionic liquid (PIL) leads to a more intense and better isolated carbonyl group band than in the case of the aprotic ionic liquid (AIL). Use of the PIL also led to better results for porous structure parameters and microstructural and morphological properties. The most significant positive effect of the PIL, however, was the increased electrokinetic stability of the activated biopolymer. The highly satisfactory results obtained at this stage suggested the use of the activated lignins to produce functional, electrochemically active hybrid systems. This was done by combining them with hydrothermally synthesized manganese oxide. The electrochemical properties of the resulting systems were determined by means of impedance spectroscopy, galvanostatic charging/discharging and cyclic voltammetry. The results confirmed that the electrode material based on lignin activated in the PIL had significantly better electrochemical properties. In cyclic charging/discharging tests a capacity of approximately 600 mAh/g was obtained, and the reversibility of the cell was 98%. The stable operation of the electrode demonstrates that the newly obtained electrode material may be successfully used in lithium-ion cells. (C) 2018 Elsevier B.V. All rights reserved.