Synthesis of Alternate Layered Structure of Ruthenate Nanosheet-Graphene Oxide for Electrochemical Applications

Abstract

As a power storage device with performances of rapid charge/discharge, long-life and high power density, electrochemical capacitor is receiving attention. As high power density materials, there are two types of materials: (1) carbon materials such as activated carbon, reduced graphene oxide (rGO), and carbon nanotube and (2) metal oxide materials such as RuO2 and MnO2. Studies have also been conducted to improve specific capacitance by supporting metal oxide on carbon materials.1 We focus on the combination of RuO2 nanosheet which has a high pseudocapacitance, with GO which has a high ion conductivity to enhance electrochemical performance. As combining method of carbon material and ruthenium oxide, we focused on click chemistry. Click chemistry is a method to combine different materials by reacting them with surface functional groups.2 Click chemistry between two-dimensional nanosheets has been used to form alternate layers.3 Since the alternate layered structures are obtained in the form of powder, broader electrochemical applications are expected. Moreover, since the alternate layers are irregularly stacked, improved substance diffusion is expected compared to the regular stacking of nanosheets by Langmuir-Blodgett or Layer-by-Layer methods. In the present study, thiol-ene reaction is considered most useful among click reactions. This is because thiol-ene reaction makes use of a combination of alkene group and thiol group, and since GO has C=C bonds, the reaction with GO is possible by only modification of RuO2 nanosheet with thiol group. We tried modification of layered ruthenium oxide with thiol group. As coupling agent, we used 3-mercaptopropyltrimethoxysilane. SEM-EDX observation results after silane coupling showed no substantial change in particle shape by silane coupling. The presence of S and Si after silane coupling was confirmed from the EDX results, indicating silane coupling was in progress. Following that we tried to exfoliate layered C3SH-RuO2 and synthesize C3SH-RuO2 nanosheet colloids. Figure shows the AFM image of substrate made by immersing silicon substrate in toluene. The AFM image showed a sheet-like morphology of approximately 1 nm thickness and 400 nm width, indicating the formation of the C3SH-RuO2 nanosheet. Alternate layered structures were synthesized by thiol-ene reaction of C3SH-RuO2 nanosheet with GO in the addition of radical initiator. SEM-EDX observation of the product shows stacking of nanosheets. The compounding of ruthenium oxide and GO was confirmed by IR, suggesting the formation of the alternate layered structure after thiol-ene reaction. Figure 1