Journal
ELECTROCHIMICA ACTA
Volume 425, Issue -, Pages -Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.electacta.2022.140708
Keywords
CNTs; Choline nitrate; Pseudocapacitance; Low temperature; Supercapacitor
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Funding
- Austrian Research Promotion Agency (FFG) Austria [39966764]
- German Federal Ministry of Education and Research (BMBF) Germany [FKZ 01DH20025]
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The study extends the working temperature range of MnO2/activated carbon supercapacitors by using a concentrated choline nitrate-based electrolyte. The hierarchical electrode design enables efficient operation even at low temperatures.
MnO2|activated carbon supercapacitors are attractive power devices that rival the electric double-layer capacitors (EDLCs) due to high reachable voltage. However, they greatly suffer from performance loss at low temperature as most of aqueous electrolytes freeze below ca. -10 degrees C. Here, a concentrated choline nitrate-based (5 mol/L aqueous ChNO3) electrolyte is applied to extend the working temperature range due to its eutectic-like properties. In such electrolyte, water acts as hydrogen bond donor for nitrate anion and low hydration energy for large choline cations favors ionic transport. The MnO2/CNT composite electrode with a hierarchical structure has been synthesized by hydrothermal process. The presence of CNTs as core component facilitates the electron conduction, while the two-dimensional MnO2 flakes grown on the surface provide electrolyte transport pathways and improve the interfacial processes (pseudocapacitive charge/discharge). Thanks to the low hydration of choline cation, the individual activated carbon (AC, negative) and MnO2/CNT (positive) electrodes are charged symmetrically up to a cell voltage of 1.8 V. Overall, due to the wide electrochemical stability window (-2.0 V) and anti-freezing properties of ChNO3-based aqueous electrolyte and the hierarchical design of the MnO2/CNT composite, the asymmetric supercapacitor operates down to -40 degrees C and displays excellent energy and coulombic efficiency with no loss of performance after several thousand cycles. This work provides a new possibility on the low temperature application of high voltage supercapacitors.
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