Polyoxometalates in Asymmetric Supercapacitors

In the present work electrochemical studies of a series of polyoxotungstate – activated carbon hybrid materials are described. The electrochemical behavior of a polyoxometalate molecule, phosphotungstic acid (H3PW12O40, PW12) was studied as negative electrode additive in asymmetric Supercapacitors (a-SCs). The strong chemisorption between polyoxometalates and carbon materials makes it possible to construct stable hybrid carbon structures. [1, 2] The methodology followed to prepare hybrid materials was described in ref. [3], where 1g of activated carbon, AC, (Super-DLC-30 kindly supplied by Norit Chemicals®) is added to 25 mL of a 10 mM aqueous solution of each of the heteropolyacids (e.g. H3PW12). The mixture is stirred for 24h at room temperature. Then, the suspensions is filtered, washed with deionized water, and dried at 100°C overnight. The amount of adsorbed PW12 is determined by weight difference. Cyclic voltammetry and galvanostatic charge-discharge cycling were performed in both two- and three- electrode cell configurations. Platinum wire and Ag/AgCl were used as counter and reference electrode, respectively. 1 M H2SO4 solution was used as electrolyte. Figure 1 shows the cyclic voltammograms at various scan rates (20, 50 and 100 mV/s) obtained in a two electrode asymmetric configuration where AC acts as positive electrode and AC-PW12 hybrid material as negative electrode. The total cell voltage used was 1.5 V. The use of the polyoxometalate adsorbed to the AC increased the stable potential window of the AC-PW12 hybrid material beyond the theoretical electrolyte decomposition, as can be seen in Figure 2