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    Fe-doped densely stacked graphene for compact capacitive energy storage
    (Elsevier Science Sa, 2023) Sinan-Tatli, Neriman; Unur-Yilmaz, Ece
    Herein, we present iron oxide (& alpha;-Fe2O3) etching and simultaneous hydrothermal reduction approach to prepare densely stacked defect-rich graphene with abundant pseudocapacitive heteroatoms (18.1 wt% O and 1.2 wt% Fe). Electrochemical measurements were conducted in acidic (1 M H2SO4) and neutral (1 M Na2SO4) aqueous media. The Fe-doped densely stacked graphene (Fe-rGO) with a low specific surface area (32.9 m2 g-1) and high particle density (1.84 g cm-3) displayed high gravimetric and volumetric capacitances of 425 F g-1 and 780 F cm-3 at 0.25 A g-1, respectively, as well as outstanding rate performance (71 % capacitance retention at 20 A g-1 in 1 M H2SO4). Moreover, Fe-rGO exhibited high electrochemical and structural stability over 5000 cycles at 10 A g-1 without any loss in capacitance. An asymmetric supercapacitor (ASC) with Fe-rGO negative electrode and MnO2/PEDOT:PSS positive electrode was assembled with aqueous 1 M Na2SO4 electrolyte. The device exhibited 17.3 Wh kg-1 specific energy and a long cyclic stability (10,000 cycles at 1 A g-1). A practical application of the device was demonstrated by powering a light emitting diode.
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    PANI-grafted radially porous MnO2 for supercapacitor applications
    (Springer, 2024) Sinan-Tatli, Neriman; Unur-Yilmaz, Ece
    In this study, manganese carbonate (MnCO3) microspheres were used as self-templates for the synthesis of hollow and radially porous MnO2 via an oxidation-etching process. Then, in situ polymerization of aniline was conducted with and without 3-aminopropyl triethoxysilane (APTES) grafting agent, resulting in the formation of PANI-grafted MnO2 (MGP) and PANI-coated MnO2 (MP), respectively. The electrochemical performances were evaluated in a three-electrode configuration using a 1 M H2SO4 aqueous electrolyte solution. Both samples showed high-specific capacitances owing to the unique MnO2 structure with radial cavities, which facilitate ion diffusion and effectively accommodate volume expansion during cycling. The MGP exhibited similar to 30% higher specific capacitance (765 F g(-1) and 586 F g(-1) at 0.25 A g(-1)) and extended cycle life (80% retention after 14,000 cycles) compared to the MP. The results demonstrate that the charge transfer efficiency and structural stability of MGP are enhanced by the formation of covalent bonds between MnO2 and PANI through grafting.