This manuscript reports on the novel insight into the development of high voltage carbon/carbon electrochemical capacitors operating in aqueous solutions of alkali metals and ammonium thiocyanates (KSCN, NaSCN, LiSCN, and NHSCN). The effect of salt concentration, electrode porosity and current collectors on the capacitance value, system stability, and power performance has been investigated. Therefore, thiocyanate-based electrolytes were recognized as cheap and highly conductive electrolytic solutions (up to 401 mS cm for NHSCN at RT) allowing a cell voltage of 1.6 V in a symmetric carbon/carbon system to be achieved. At the same time, they display an attractive redox activity, enhancing the energy of the device with a good performance during cycling.
This review focuses on describing the current state-of-the-art research in the synthesis of 3D architectures for electrochemical capacitor applications. The selection is based on both template and non-template strategies. Particular attention has been paid to carbon materials because of their structural interconnection, as they create not only the desired hierarchical porous channels but also ensure high conductivity and mechanical stability. A comprehensive overview of electrode materials is presented here with a detailed discussion of composite solutions, including their advantages and disadvantages. Numerous examples from the literature are presented for individual solutions. The future challenges posed for this type of material are finally summarized.
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