Development of a 4.2 V aqueous hybrid electrochemical capacitor based on MnO2 positive and protected Li negative electrodes

An aqueous hybrid electrochemical capacitor consisting of a capacitive manganese oxide (MnO2) positive electrode and a water-stable, protected Li negative electrode in near-neutral aqueous electrolyte (1.0 M Li2SO4, pH = 5.5) is demonstrated. Galvanostatic charge/discharge cycling tests were conducted with pouched cells, offering a cell voltage of 4.2 V with maximum specific energy of 753 W h kg(-1) based on the positive electrode. The combination of a pseudocapacitive MnO2 positive and a Li negative electrode offers high specific charge and cell voltage, resulting in an aqueous hybrid electrochemical capacitor having exceptionally high specific energy.ArticleJOURNAL OF POWER SOURCES. 241:572-577 (2013)journal articl

Evidence of Strong Metal-Support Interaction between Pt and Crystalline RuO2 Nanosheets by In-Situ AFM

The enhancement in durability of Pt nanoparticles modified by nanostructured RuO2 was studied using a model electrode consisting of vacuum deposited Pt on single crystalline RuO2 nanosheets coated on highly oriented pyrolytic graphite (HOPG) surface with sub-monolayer coverage. Atomic force microscopy images showed that Pt on HOPG aggregated and tended to form 3-dimensional islands. On the other hand, Pt formed a well-defined, 2-dimensional over-layer on the RuO2 nanosheet surface. In-situ atomic force microscopy images showed that deposited Pt on the HOPG surface readily dissolved and easily migrated with potential cycling in sulfuric acid, while no such phenomena could be observed on the RuO2 nanosheets. The results indicate that RuO2 nanosheet has a strong affinity toward Pt, namely strong metal-support interaction for Pt, which can be considered as one of the reasons for the enhanced durability of Pt/C modified by RuO2 nanosheets.ArticleJOURNAL OF THE ELECTROCHEMICAL SOCIETY. 161(3):F360-F363 (2014)journal articl

Suppression of CO Adsorption on PtRu/C and Pt/C with RuO2 Nanosheets

RuO2 nanosheets were studied as a promotor for the hydrogen oxidation reaction in the presence of 300 ppm CO/H-2. The hydrogen oxidation current in 300 ppm CO/H-2 for RuO2 nanosheet modified PtRu/C catalyst (RuO2:Pt:Ru = 0.5:1:1 (molar ratio)) exhibited higher CO tolerance than Pt1Ru1/C and Pt2Ru3/C. Based on hydrodynamic voltammetry, chronoamperometry and CO stripping voltammetry, the addition of RuO2 nanosheets is suggested to suppress CO adsorption on the catalyst surface, resulting in an improvement in CO tolerance. (C) The Author(s) 2015. Published by ECS.ArticleECS ELECTROCHEMISTRY LETTERS. 4(5):F35-F37 (2015)journal articl

Influence of the RuO2 Nanosheet Content in RuO2 Nanosheet-Pt/C Composite Toward Improved Performance of Oxygen Reduction Electrocatalysts

A series of composite electrocatalysts composed of RuO2 nanosheets and carbon supported Pt (RuO(2)ns-Pt/C) has been synthesized by mixing different amounts of commercial 50 wt% Pt/C with RuO(2)ns derived from exfoliation of layered K0.2RuO2.1 center dot nH(2)O. The oxygen reduction activity and stability of the different electrocatalysts has been evaluated as a function of the nanosheet content in the composite electrocatalysts. An increase in initial activity was observed for composite electrocatalyst with RuO2/Pt<0.4. After conducting accelerated durability tests, the RuO(2)ns-Pt/C composite electrocatalyst with RuO2/Pt = 0.3 exhibited a 25% higher mass activity toward oxygen reduction than the pristine Pt/C electrocatalyst.ArticleJOURNAL OF THE ELECTROCHEMICAL SOCIETY. 161(3):F318-F322 (2014)journal articl

Towards Implantable Bio-Supercapacitors: Pseudocapacitance of Ruthenium Oxide Nanoparticles and Nanosheets in Acids, Buffered Solutions, and Bioelectrolytes

Metal oxides, in particular ruthenium-based oxides, are promising electrode materials for aqueous pseudocapacitors. Strong acids or bases are favored over neutral electrolytes owing to the higher capacitance. Here we explore the pseudocapacitive behavior of ruthenium oxide nanoparticles and nanosheets in near neutral pH as an environmentally benign electrolyte. The pseudocapacitive charge storage in poorly-crystalline hydrous RuO2 nanoparticles, and highly-crystalline RuO2 nanosheets were investigated in acetic acid-lithium acetate (AcOH-AcOLi) buffered solutions. It is shown that capacitance values as high as 1,038 F g(-1) can be achieved in AcOH-AcOLi buffered solutions with RuO2 nanosheets, which is 44% higher than the benchmark RuO2 nH(2)O in H2SO4 electrolyte (720 F g(-1)). Furthermore, comparable performance was obtained in phosphate buffered saline and fetal bovine serum. The mechanism of the pseudocapacitive properties is discussed based on the difference in the surface redox behavior of different RuO2 nanomaterials in acid, neutral, buffered solutions, and in weak acid. (C) The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. All rights reserved.ArticleJOURNAL OF THE ELECTROCHEMICAL SOCIETY. 162(5):A5001-A5006 (2015)journal articl

Catalytic etching of synthetic diamond crystallites by iron

For the expansion of the functionality of diamond crystallites by modification of surface morphology, catalytic etching of synthetic diamond crystallites at 1173 K by iron, which were loaded by the impregnation method using an aqueous solution of iron nitrate; in a streaming mixed gas (pH(2) = 0.1 MPa, pN(2) = 0.9 MPa), has been investigated by scanning electron microscopy (SEM) and Raman spectroscopy. The dependence of the crystal planes {111} and {100}, of the diamond crystallites and the loading amount of iron on the diamond on the etching behavior by iron particles, the morphology of the etch pits, and potential formation of iron carbide through the catalytic etching, were discussed.ArticleAPPLIED SURFACE SCIENCEjournal articl

Catalytic etching of {100}-oriented diamond coating with Fe, Co, Ni, and Pt nanoparticles under hydrogen

Etching of a highly {100}-oriented diamond coating, {100}HODC, with hydrogen gas using Fe, Co, Ni, and Pt nanoparticles as a catalyst was examined at high temperatures over 700 degrees C by high-resolution scanning electron microscopy and Raman spectroscopy. The metal atoms vacuum-evaporated onto the {100}HODC formed nanopartides themselves when heated at high temperatures; e.g. 700 degrees C, in a flowing gas mixture of H(2) (10%) + N(2) (90%). At 800 degrees C. short nano-channels and etch pits holding metal nanoparticles were formed by Fe. Co. and Ni. The shapes of the Co and Ni nanoparticles in the etch pits were affected by the shape of the etch pits; reversed pyramidal shape. On the other hand, the top view of the Fe nanoparticles embedded in the etch pits showed a distorted round shape, probably due to the formation of something such as iron carbide, while the carbon content was unknown. Apparently, etching of the {100}HODC by Pt nanoparticles was observed after the treatment at 1000 degrees C. The difference in the catalytic etching behavior among these metal particles, the potential etching mechanism of diamonds with hydrogen by metal nanoparticles, probably as melted metal nanoparticles, and the formation mechanism of vacant etch pits were discussed.ArticleDIAMOND AND RELATED MATERIALSjournal articl

Structural analyses of RuO(2)-TiO(2)/Ti and IrO(2)-RuO(2)-TiO(2)/Ti anodes used in industrial chlor-alkali membrane processes

The morphology and composition of RuO(2)-TiO(2)/Ti and IrO(2)-RuO(2)-TiO(2)/Ti anodes, which have been used for the production of chlorine for more than 10 years, were analyzed by various methods; such as high-resolution scanning electron microscopy, high-resolution Auger electron spectroscopy, electron probe X-ray emission microanalysis and X-ray diffraction analysis. Drastic changes in the surface morphology, including partial exfoliation of a small amount of the oxide layer and a reduction in the content of ruthenium species through dissolution, were observed for the RuO(2)-TiO(2)/Ti anode. For the IrO(2)-RuO(2)-TiO(2)/Ti anode, on the other hand, there were moderate changes in the surface morphology and moderate dissolution of iridium and ruthenium species.ArticleJOURNAL OF APPLIED ELECTROCHEMISTRYjournal articl

Steam activation of boron doped diamond electrodes

Boron doped diamond (BDD) electrodes were activated in steam at various temperatures, resulting in high quality BDD electrodes with a porous microstructure. Distinct columnar structures were observed by scanning electron microscopy. The electrochemically active surface area of the steam-activated BDD was up to 20 times larger than the pristine BDD electrode owing to the porous texture. In addition, a widening of the potential window was observed after steam activation, suggesting that the quality of BDD was enhanced due to oxidative removal of graphitic impurities during the activation process.ArticleELECTROCHIMICA ACTA. 56(16):5599-5604 (2011)journal articl

4 V class aqueous hybrid electrochemical capacitor with battery-like capacity

A new aqueous hybrid electrochemical capacitor consisting of a porous positive capacitive electrode and a water-stable multilayered Li negative electrode is demonstrated. The new cell design affords cell voltages close to 4 V in a mild aqueous electrolyte. Application of a pseudocapacitive positive electrode with high specific charge results in specific energy comparable to present rechargeable batteries.ArticleRSC ADVANCES. 2(32):12144-12147 (2012)journal articl