Chen-Ching Wang

Nanostructures and Capacitive Characteristics of Hydrous Manganese Oxide Prepared by Electrochemical Deposition

Amorphous manganese oxide deposits with nanostructures (denoted as a-MnO x .nH 2 O) were electrochemically deposited onto graphite substrates from 0.16 M MnSO 4 .5H 2 O with pH 5.6 by means of the potentiostatic, galvanostatic, and potentiodynamic techniques. The maximum specific capacitance of a-MnO x .nH 2 O deposits plated in different modes, measured from cyclic voltammetry at 25 mV s -1 , is about 230 F g -1 in a potential window of 1.0 V. The high electrochemical reversibility, high-power characteristics, good stability, and improved frequency responses in 0.1 M Na 2 SO 4 for these nanostructured a-MnO x .nH 2 O deposits prepared by electrochemical methods demonstrate their promising potential in the application to electrochemical supercapacitors. The nanostructure of a-MnO x .nH 2 O, clearly observed by means of a scanning electron microscope, was found to depend strongly on the deposition mode. The similar capacitive performance of all deposits prepared in different modes was attributable to their nonstoichiometric nature with a very similar oxidation state, demonstrated by XPS spectra.

Improving the utilization of ruthenium oxide within thick carbon–ruthenium oxide composites by annealing and anodizing for electrochemical supercapacitors

The effects of annealing in air and anodizing on the capacitive behavior of carbon–ruthenium (denoted as C–Ru) composites fabricated by wet impregnation were investigated in 0.1 M H2SO4 by cyclic voltammetry (CV) and chronopotentiometry (CP). The utilization of Ru species within the thick composites (≈1000 μm) was greatly promoted by annealing in air at 240 °C for 8 h and anodizing in 0.1 M H2SO4 at 1.2 V for 1.5 h, due to the formation of Ru oxide and the transformation into a hydrous nature and the maximal specific capacity of Ru oxide (760 F g−1 based on RuO2) could be obtained. The crystalline information of the composites with annealing at different temperatures was obtained from X-ray diffraction (XRD) patterns. The morphology of C–Ru composites was examined by scanning electron microscope (SEM). The specific surface area and pore-size distribution of the composites with annealing and/or anodizing were analyzed by the BET method.

Electrochemical and Textural Characteristics of ( Ru ­ Sn ) O x ⋅ n H 2 O for Supercapacitors Effects of Composition and Annealing

Nanostructured hydrous ruthenium-tin oxides [denoted as (Ru-Sn)O x .nH 2 O] with variable Sn contents were fabricated by a modified sol-gel process. The mean particle size of pristine (Ru-Sn)O x .nH 2 O, smaller than 3 nm, was monotonously decreased with increasing the mole fraction of Sn in precursor solutions. The introduction of tin within the RuO x .nH 2 O matrix with annealing in air between 150 and 250°C for 2 h promoted the utilization of electroactive oxyruthenium species (reaching a maximum capacitance of ca. 860 F/g based on RuO x ) when the Sn content was lower or equal to 50 atom %. The capacitive performance of (Ru-Sn)O x .nH 2 O was studied by cyclic voltammetry. The compositions of (Ru-Sn)O x .nH 2 O oxide were obtained from energy-dispersive spectroscopic analysis. The textural characteristics of these binary oxides were examined by means of transmission electron microscopy, electron diffraction, and X-ray diffraction analysis.