Ozlem Sel

The simple and eco‐friendly preparation of microsupercapacitor remains a great challenge. Here are presented the preparation and the characterizations of an all‐solid symmetric micro‐supercapacitor based on a new composite formed of highly ordered graphene sheets due to the presence of polydopamine between the layers, which present a d‐spacing of 0.356 nm. This graphene‐polydopamine composite is prepared by electroreduction of graphene oxide (GO) followed by the electrooxidation of dopamine added into the initial solution, i.e., after GO reduction. In Na 2 SO 4 solution, this composite material shows excellent capacitance and stability even at a high scan rate (2 V s −1 ) and a very low relaxation time (τ 0 ) of 62 ms. This value is in very good agreement with the high transfer kinetic and low transfer resistance values of the ions implied in the charge storage process (Na + ·2H 2 O and Na + ) determined by ac‐electrogravimetry. Finally, it is shown that the all‐solid micro‐supercapacitor (interdigitated electrodes obtained using a CO 2 laser and Na 2 SO 4 /PVA hydrogel) prepared with this new composite delivers a remarkable energy density of 6.36 mWh cm −3 for a power density of 0.22 W cm −3 and exhibits excellent cycling stability (98% of retention after 10 000 cycles at 2 V s −1 ).

To reach a deeper understanding of the charge storage mechanisms of electrode materials is one of the challenges toward improving their energy storage performance. Herein, we investigate the interfacial ion exchange of a composite electrode made of carbon nanotube/poly(ortho-phenylenediamine) (CNT/PoPD) in a 1M NaCl aqueous electrolyte via advanced electrogravimetric analyses based on electrochemical quartz crystal microbalance (EQCM). Classical EQCM at different scan rates of the potential revealed the complex electrogravimetric behavior likely due to multi-species participation at different temporal scales. Thereafter, in order to better understand the behavior of each species (ions, counter ions, and co-ions) in the charge compensation mechanism, the electrogravimetric impedance spectroscopy analysis (also called ac-electrogravimetry) was pursued. Ac-electrogravimetry revealed the role of each species where Na+ cations and Cl− anions as well as protons participate in the charge compensation mechanism of the CNT/PoPD composite with different kinetics and proportions. The water molecules with opposite flux direction with the cations are also detected, suggesting their exclusion during cationic species transfer. Having analyzed ac-electrogravimetry responses in depth, the synergistic interaction between the CNT and PoPD is highlighted, revealing the improved accessibility of species to new sites in the composite.