Textural and Capacitive Characteristics of Hydrothermally Derived RuO₂·xH₂O Nanocrystallites:  Independent Control of Crystal Size and Water Content

Abstract

RuO 2 ‚xH 2 O nanoparticulates in different crystal sizes with various water contents were prepared via a hydrothermal synthesis route, successfully demonstrating the independent control of crystal size and water content of RuO 2 ‚xH 2 O. The crystalline and hydrous nature of hydrothermally derived RuO 2 ‚xH 2 O particulates not only reduces the proton diffusion resistance but also enhances the electronic conductivity for the redox transitions of active species. Novel and unique properties of hydrothermally derived RuO 2 ‚ xH 2 O, i.e., effective inhibition of crystallite coalescence upon annealing, relatively high thermal stability, and maintenance of the original nanostructure, are attributable to the coalescence barrier of RuO 2 ‚xH 2 O crystallites due to the lattice energy. Maintaining/fine-tuning the original nanostructure of annealed RuO 2 ‚ xH 2 O crystallites with high mesoporosity favors the penetration of electrolytes into the whole oxide matrix. This effect of not only reducing the proton diffusion resistance but also improving the electron pathways promotes the utilization of RuO 2 ‚xH 2 O in supercapacitor applications.

Pseudocapacitive Properties of Nano‐structured Anhydrous Ruthenium Oxide Thin Film Prepared by Electrostatic Spray Deposition and Electrochemical Lithiation/Delithiation

“…After discharged to 0.8 V (Figure 3c), the LiRuO 2 and the crystalline RuO 2 phase disappeared, leading to a featureless XRD pattern (Figure 4c). Similar featureless XRD patterns (Figure 4d) were obtained when charged to 4.3 V with the extraction of Li (Figure 3d), which suggests the formation of nano-structured RuO 2 [9,28]. The formation of nanocrystalline RuO 2 after electrochemical lithiation/delithiation was confirmed by Raman spectroscopy (Raman data not shown).…”

“…The RuO 2 thin film prepared by ESD showed characteristic peaks of (110), (101) and (211), which could be indexed to crystalline ruthenium oxide [17,19,20]. It was reported that a complete crystalline phase of RuO 2 could be obtained after a post-heat treatment at relatively high temperatures over 300°C for thermally prepared or sol-gel derived RuO 2 [5][6][7][8][9]. Figure 2 indicates that ESD could prepare crystalline RuO 2 thin films on a Pt-coated Si wafer heated at 300°C in a single step.…”

Nanostructured Material Fabrication for Energy Conversion

“…It is important to highlight that, for the single crystal RuO 2 , the three Raman modes are located at about 528, 646, and 716 cm -1 [16]. In our case, all the three peaks show a red-shift of about 20 cm -1 that can be attributed to the nanoscale nature of as-deposited RuO 2 as reported by several authors [14][15][16]. Thus, on the basis of these results we can conclude that the deposit that we have obtained inside the channels of alumina template is amorphous hydrated RuO 2 .…”

“…In the case on nanotubes, Raman spectrum was reported in Fig. 8 [14]. Furthermore, it can be observed a weak and broad peak at 390 cm -1 , which has not yet been identified.…”

Soft template synthesis of mesoporous Co3O4/RuO2·xH2O composites for electrochemical capacitors

“…Compared with sample (b), such mesoporous microstructures and high surface area of sample (a) are believed to facilitate larger capacitance and higher power density because ions transfer rate in the pore system and the extent of electrode/electrolyte interfacial area are determined by the porosity of the electrode material. That means that these original mesopores make the penetration of electrolytes into the whole oxide matrix facilely, which further reduce the diffusion resistance [33]. In addition, larger surface area of sample (a) is good to surface reactions, which is important in the enhancement of the electrochemical properties.…”