Local Atomic Structure and Conduction Mechanism of Nanocrystalline Hydrous RuO₂ from X-ray Scattering

Abstract

Hydrous ruthenium oxide (RuO2·xH2O or RuO x H y ) is a mixed proton−electron conductor which could be used in fuel cells and ultracapacitors. Its charge-storage (pseudocapacitance) and electrocatalytic properties vary with water content and are maximized near the composition RuO2·0.5 mol % H2O. We studied the atomic structure of RuO2·xH2O as a function of water content from x = 0.84 to 0.02 using X-ray diffraction and atomic pair density function (PDF). Even though the diffraction patterns of samples containing 0.84 to 0.35 mole of water are suggestive of “amorphous” structures, the PDF analysis clearly shows that up to 0.7 nm, the short-range atomic structure of all of these RuO2·xH2O samples resembles that of the anhydrous rutile RuO2 structure. We conclude that RuO2·xH2O is a composite of anhydrous rutile-like RuO2 nanocrystals dispersed by boundaries of structural water associated with Ru−O. Metallic conduction is supported by the rutile-like nanocrystals, while proton conduction is facilitated by the structural water along the grain boundaries. This structural picture explains the charge-storage and electrocatalytic properties of RuO2·xH2O in terms of competing percolation networks of metallic and protonic conduction pathways, that vary in volume as a function of the water content of the RuO2·xH2O. The control and optimization of electron and proton conducting volumes and pathways will lead to improved performance and guide the design of new materials.

Organometallic Derivatives of Cyclotriphosphazene as Precursors of Nanostructured Metallic Materials: A New Solid State Method

“…Main diffraction peaks were seen at 2θ = 28.08, 35.18 and 54.8 ( Fig. 4c) and agree well with those reported for RuO 2 [60][61][62]. The average particle size was estimated to be 11 nm from the Debye-Scherrer relation [58].…”

Laser Forward Transfer of Electronic and Power Generating Materials

“…The rapid insertion and release of protons and electrons through the material enables a large pseudocapacitance effect, which, in combination with a high specific surface area, leads to the large amounts of charge stored in the material (Trasatti, 1994;Sarangapani, 1996). This effect is enhanced by the presence of structural water in the lattice that provides nanostructured percolation pathways for proton conduction into the bulk of the material (Dmowski, 2002).…”

Synthesis of ordered mesoporous ruthenium by lyotropic liquid crystals and its electrochemical conversion to mesoporous ruthenium oxide with high surface area

“…In addition to metallic Ru, high surface area ruthenium oxide is also an important material for various applications, including electrocatalysts for chlorine evolution [24], electrochemical capacitor electrodes [25][26][27][28][29], as well as fuel cell electrocatalysts [30][31][32][33][34][35][36][37][38][39]. The small particle size (1-2 nm) and the existence of appreciable pores are important requirements for the high capacitance [40][41][42]. The synthesis of high capacitance RuO 2 (~700 F g -1 ) have been conducted mainly by sol-gel synthesis, leading to materials with random micropores [25,26].…”