Fabrication of Ruthenium Oxide-Coated Si Nanowire-Based Supercapacitors

icon Fabrication of Ruthenium Oxide-Coated Si Nanowire-Based Supercapacitors

W. Zheng, Q. Chen, D. Wang, C. V. Thompson
Sponsorship: Singapore-MIT Alliance for Research and Technology

Supercapacitors are electrochemical devices that have high power density and long cycle life. Pseudo-capacitors are a type of supercapacitor that involves reversible surface reduction/oxidiation reactions. Among all the pseudo-capacitive materials, ruthenium oxide is the most promising due to its high specific capacitance, excellent cyclability, and high conductivity. While researchers have been developing supercapacitors based on ruthenium oxide or its composite with other materials such as carbon nanotubes (CNTs), there has been little study on ruthenium oxide-Si composite electrodes. In earlier work, we demonstrated the feasibility of using metal assisted chemical etching (MACE) to fabricate Si nanowires for on-chip MOS capacitors. Here we use an ordered vertical array of Si nanowires from a similar wet etching process named metal-assisted anodic etcing (MAAE) to fabricate on-chip supercapacitors.
Atomic layer deposition (ALD) is used to deposit ruthenium oxide on silicon nanowires due to its conformal coating of high aspect ratio structures. The use of ALD also provides precise control of the ruthenium oxide film thickness. As pseudo-capacitive reactions occur at
the surface of ruthenium oxide, the high aspect ratio Si nanowire structures coated with ruthenium oxide has a high surface area of accessible ruthenium oxide per area of substrate surface, which thus leads to a high energy storage capacitance. We have developed an ALD process for coating of ruthenium oxide on Si nanowires generated by MAAE. The composite structure showed a con-tinuous coating of well-distributed particles (Figure 1). High-resolution transmission electron microscopy characterization and x-ray diffraction analysis con-firmed that most nanoparticles were in the form of elemental ruthenium. We are currently investigating the electrochemical performance of this composite material in an aqueous electrolyte using a three-electrode setup. The preliminary data showed that the specific capacitance scaled well with the length of silicon nanowires in this aqueous electrolyte (Figure 2).
Meanwhile, we are fabricating solid-state micro-supercapacitors based on use of solid electroltyes. We are interested in studying the performance dependence of the solid-state device on both Si nanowire aspect ratios and ALD cycle numbers.

nanowires

si nanowire

FURTHER READING
  • S. W. Chang, J. Oh, S. T. Boles, and C. V. Thompson, “Fabrication of silicon nanopillar-based nanocapacitor arrays,” Appl. Phys. Lett., vol. 96, p. 153108, 2010.
  • S. W. Chang, V. P. Chuang, S. T. Boles, C. A. Ross, and C. V. Thompson, “Densely-packed arrays of ultrahigh-aspect-ratio silicon nanowire fabricated using block copolymer lithography and metal-assisted etching,” Adv. Funct. Mater., vol. 19, p. 2495, 2009.
  • C. Q. Lai, W. Zheng, W. K. Choi, and C. V. Thompson, “Metal Assisted Anodic Etching of Silicon,” Nanoscale, vol. 25, p. 11123, 20
Last Updated on Thursday, 21 July 2016 20:23