• PDF / 783,984 Bytes
• 6 Pages / 584.957 x 782.986 pts Page_size
• 101 Downloads / 261 Views

DOWNLOAD

REPORT

---

Self-assembly bioinspired peptide nanotubes (PNT) demonstrate diverse physical properties such as optical, piezoelectric, fluidic, etc. In this work, we present our research on environmentally clean bioinspired peptide nanostructured material, to be applied to energy storage devices-supercapacitors (SC). Such an application is based on our recently developed PNT physical vapor deposition technology. It has been found that PNT fine structure and its wettability in electrolytes are the critical factors for a strong variation of the SC capacitance. We show that PNT-coated carbon electrodes enlarge the double-layer capacitance by dozens of times; reaching 800 mF/cm2 in a sulfuric acid (normalizing to the electrode geometric surface area of carbon background electrode). The discovered effect is provided by hollow PNT possessing numerous hydrophilic nanoscale-diameter channels, elongated along the PNT axis, which dramatically increase the functional area of carbon electrodes. Another type of the observed PNT morphology is fiberlike highly hydrophobic PNT rods, which do not contribute to the SC capacitance.

I. INTRODUCTION

Batteries and supercapacitors (SC) are two large groups of modern energy storage devices.1,2 SC have been developed as a complement or replacement of batteries, since they can operate at high charge/discharge rates over almost an unlimited number of cycles due to involved negligible chemical charge transfer reactions.2,3 However, SC have a much lower energy density than batteries, therefore the challenge in this field is the development of high-surface-area electrodes.4 Nanomaterials, such as nanotubes, nanowires, and nanoparticles, become increasingly important candidates for electrodes of electrochemical energy storage devices. Their nanoscale dimensions increase the electrolyte/electrode area, which leads to the enlargement of capacitance and energy density.5 A wide range of inorganic nanomaterials was used for SC electrode applications.3,6–8 However, the research mainly focused on carbon-based nanomaterials (CBN), such as nanoparticles, carbon nanotubes, and carbon fabrics.9 CBN have satisfied all the requirements for energy storage application, including a large surface area, high conductivity, electrochemical stability, and relatively low cost.4,9,10 Nevertheless, specific capacitance obtained from CBNs is much lower than expected.3,9 This has been mainly attributed to poor a)

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0213 J. Mater. Res., Vol. 25, No. 8, Aug 2010

http://journals.cambridge.org

Downloaded: 10 Feb 2015

wettability properties of untreated carbon materials (the intrinsic contact angle of essentially graphite material is 86
11), causing a limited access of electrolyte to the electrode material. The nonwetted surface area does not contribute to the capacitance, because an electrical double layer is generated only on the area wetted by an electrolyte (functional area).3,9,12 To improve the wettability of CBN, a surface functionalizi