Electrochimica Acta, Vol.295, 302-315, 2019
Supercapacitive properties, anomalous diffusion, and porous behavior of nanostructured mixed metal oxides containing Sn, Ru, and Ir
Different nanostructured mixed metal oxide (MMOs) electrodes containing Sn, Ru, and Ir supported on titanium with the nominal composition Ti/[Sn0.5Ru(0.5-x) Ir-(x)]O-2 were prepared using the drop-coating method. SEM analysis revealed the presence of oxide islands in the microsized domains of ca. 50 mu m separated from each other by cracks. On the contrary, analysis of the nanosized domains revealed the presence of nanostructures containing rectangular grains with an average diameter of ca. 200 nm. The discrepancy between the nominal and real oxide compositions was attributed to volatilization of Sn during the heat treatment. XRD analysis revealed a poor degree of crystallinity and an average crystallite size of 15 +/- 4 nm. Different electrochemical studies revealed higher specific pseudocapacitances in the range of 175-222 F g(-1) for the MMO containing 50 mol% Ir. The low values obtained for the morphology factor (0.11 <= phi <= 0.33) indicate a relatively narrow interval of 11-33% for the active surface regions confined to the inner surface regions of the oxide layers. The chronoamperometric findings obtained for short times (t <= 50 ms) permitted evaluation of the electrical double-layer capacitance (C-edl), with verified maximum values in the range of 68-75 F g(-1) for the MMO containing 50 mol% Ir. On the contrary, the experimental findings obtained for long times (0.1 s <= t <= 3 s) revealed that the reversible solidstate Faradaic reactions did not exhibit a Fickian behavior. The impedance analysis revealed that MMOs exhibit a porous electrode behavior (De Levie's model) permitting the determination of the pseudoca-pacitance and the resistance of the electrolyte inside the pores. (C) 2018 Elsevier Ltd. All rights reserved.