Redox Capacitors Based on Organic Monomers

The main fault of electrodes based on ECPs is their limited chemical reproducibility and thus insufficient cyclability in aqueous electrolytes. Therefore, replacement of ECPs in PsCs by a redox couple based on organic monomers covalently bound to the carbon support of a highly dispersed carbon electrode is considered (Hashmi SA, et al 2004). Naturally, a synergistic effect between the EDL capacitance charging and the concurrent redox (pseudocapacitive) reaction occurs in this case. The latter, alongside with EDL capacitance, contributes to the overall capacitance of such a composite electrode. 

The following asymmetrical PsC capacitor was studied as a typical example of a redox capacitor. 1,2-dihydroxybenzene (DHB also referred to as o-benzoquinone and catechol) obtained by modification of a carbon electrode was used in it as a positive electrode. The negative electrode used was an anthraquinone (AQ)-modified carbon electrode (Algharaibeh and Pickup, 2011). 

A Spectracarb 2225 carbon fabric (Engineered Fibres Technologies) was used as a basis for the synthesis of an AQ-modified carbon cloth (C-AQ) electrode. This cloth was immersed into the salt of anthraquinone-1-diazonium chloride 0.5 ZnCl2 in acetone. Then, water and 50 wt% hypophosphorous acid were added. Then, the thus-modified cloth was washed by deionized water and dried at 110°C for 20 min. 

DHB-modified carbon cloth electrodes (C-DHBs) were manufactured by the modification of a Spectracarb 2225 carbon cloth. This cloth was immersed into 0.25 M HCl and then 4-aminocatechol and water (8 ml) were added. This was followed by the cooling in an ice bath and slow addition of 3 M NaN02. After that, the modified cloth was washed by deionized water and dried in air. 

The separator used was a Nation membrane. Each electrode was separated by a carbon paper disk (Toray TGP-H-090) from the Ti plate current tap to minimize contact resistance. The assembled cell was immersed into 1M H2S04(aq) to impregnate electrodes by electrolyte. 

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