Dai Mochizuki

Synthesis and Oxygen Electrocatalysis of Iridium Oxide Nanosheets

AbstractRutile-type iridium dioxide (IrO2) is a well-known electrocatalyst, and its nanoparticle form has recently attracted attention as catalysts and co-catalysts in electrolyzers and fuel cells. In this study, we have successfully synthesized single crystalline iridium dioxide (IrO2) nanosheets with thickness of less than 0.7xa0nm via exfoliation of layered iridic acid HxIryOz·nH2O, which was prepared via proton exchange of layered potassium iridate, KxIryOz·nH2O. The electrochemically active surface area of the IrO2 nanosheet electrode was similar to or slightly lower than that of 3-nm IrO2 nanoparticles. Despite the lower active surface area, the mass activity for oxygen evolution reaction of IrO2 nanosheets was six times higher compared to that of IrO2 nanoparticles in 0.1xa0M HClO4 at 1.55xa0V vs. the reversible hydrogen electrode (17.4 vs. 2.9xa0Axa0g−1). When IrO2 nanosheets were added to commercial Pt/C as a co-catalyst, increased stability against high potential cycling was obtained. After potential cycling between 1.0 and 1.5xa0V, the composite catalyst exhibited two times higher oxygen reduction activity compared to non-modified Pt/C. This durability enhancement is attributed to the suppression of the particle growth during the potential cycling test by the modification with IrO2 nanosheets.n Graphical AbstractIrO2 nanosheets are highly active as electrocatalysts for O2 evolution and O2 reduction

Energy Storage Systems

Oxide nanosheets prepared via chemical exfoliation of ion-exchangeable layered transition metal oxides composed of of Ru, Mn, Co, Ti, etc., are attracting increased interest as electrode materials for electrochemical energy storage devices such as supercapacitors and rechargeable batteries. This interest comes from the possibility of nanosheets affording high surface area and microstructural control. Supercapacitors, for example, store energy at the electrode/electrolyte interface. Thus, increasing the amount of electrified interface directly contributes to high capacitance and energy density. Controlling the micro-/meso-porosity of the electrode is also important in terms of power performance. Porous nanosheet electrodes have also been studied for battery applications, especially for high rate charge/discharging.

Proton tunneling in low dimensional cesium silicate LDS-1

In low dimensional cesium silicate LDS-1 (monoclinic phase of CsHSi2O5), anomalous infrared absorption bands observed at 93, 155, 1210, and 1220 cm(-1) are assigned to the vibrational mode of protons, which contribute to the strong hydrogen bonding between terminal oxygen atoms of silicate chain (O-O distance = 2.45 Å). The integrated absorbance (oscillator strength) for those modes is drastically enhanced at low temperatures. The analysis of integrated absorbance employing two different anharmonic double-minimum potentials makes clear that proton tunneling through the potential barrier yields an energy splitting of the ground state. The absorption bands at 93 and 155 cm(-1), which correspond to the different vibrational modes of protons, are attributed to the optical transition between the splitting levels (excitation from the ground state (n = 0) to the first excited state (n = 1)). Moreover, the absorption bands at 1210 and 1220 cm(-1) are identified as the optical transition from the ground state (n = 0) to the third excited state (n = 3). Weak Coulomb interactions in between the adjacent protons generate two types of vibrational modes: symmetric mode (93 and 1210 cm(-1)) and asymmetric mode (155 and 1220 cm(-1)). The broad absorption at 100-600 cm(-1) reveals an emergence of collective mode due to the vibration of silicate chain coupled not only with the local oscillation of Cs(+) but also with the proton oscillation relevant to the second excited state (n = 2).