Electrochemical Chem/Bio Sensing Based on Modified Graphene The extraordinary electrical properties of graphene make it an excellent candidate for next generation electrochemical sensors for gas or liquid sensing. Our efforts focused on the growth and modification of graphene sheets with metal nanoparticles through electroless deposition, and their transfer onto different transducers (e.g., screen printed electrodes and interdigitated electrodes) to achieve various characteristics depending on the final desired applications. Further modification of the metal nanoparticle with biomarkers and biomolecules for more specific recognition was also explored. Selective detection of a number of analytes, ranging from glucose to hydrogen peroxide to PDDE, was demonstrated. Selected Publications A. Gutés, B.-Y. Lee, C. Carraro, W. Mickelson, S.-W. Lee, R. Maboudian, “Impedimetric graphene-based aptasensor for the detection of polybrominated diphenyl ether“, RSC Nanoscale 5, 6048-6052 (2013). A. Gutés, B. Hsia, A. Sussman, W. Mickelson, A. Zettl, C. Carraro, R. Maboudian, “Graphene decoration with metal nanoparticles: Towards easy integration for sensing applications”, RSC Nanoscale, 4, 438-440 (2012).
High Surface Area Nanomaterials for Supercapacitors Electrochemical storage devices, in particular batteries and supercapacitors, are devices with the potential to meet the energy storage demands of the future. Batteries are high energy capacity devices which store energy through redox reactions in the bulk material of the device. Supercapacitors are high power devices which store energy in the electrochemical double layer. We developed and characterized the performance of several new materials for high-energy density supercapacitor. In particular, we investigated high surface area (i.e., high storage capacity) electrode materials including porous silicon nanowires grown from bulk silicon, silicon carbide nanowires, and graphene. Significant efforts were made to understand the relationship between synthesis conditions and material properties (e.g., conductance, porosity, and stability). Through this fundamental knowledge, these materials were optimized for use in supercapacitor devices. Selected Publications S. Ortaboy, J.P. Alper, F. Rossi, G. Bertoni, G. Salviati, C. Carraro, R. Maboudian, “MnOx-decorated carbonized porous silicon nanowire electrodes for high-performance supercapacitors,” Energy and Environmental Science, in press. J. P. Alper, S. Wang, F. Rossi, G. Salviati, N. Yiu, C. Carraro, R. Maboudian, “Ultra-Thin Carbon Coatings on Porous Silicon Nanowires: Materials for Extremely High Energy Density Planar Micro-Supercapacitors,” Nano Letters 14, 1843–1847 (2014).
Nano-materials for High Temperature Energy Storage Supercapacitors that can withstand harsh environments such as high temperature (i.e., >300 ° C) have received interest due to their relevance for space, military, and electric vehicle applications. This motivation has sparked the search for suitable active materials and electrolytes that can work stably and reliably at high temperatures. Silicon carbide is known to be stable in many harsh physicochemical environments, including high-temperature oxidizing environments. Yttria-stabilized Zirconia (YSZ) has a high ionic conductivity at T > 400°C and is hence a promising solid electrolyte for high temperature energy storage. We investigated the use of YSZ in conjunction with SiC nanowires for the development of high-temperature stable supercapacitors. Good cycling stability was demonstrated with a capacitance retention of over 60% after 10,000 cycles at the operation temperature of 450 ° C. Selected Publications C.-H. Chang, B. Hsia, J. P. Alper, S. Wang, L. E. Luna, C. Carraro, S.-Y. Lu, R. Maboudian, “High-temperature All Solid-state Microsupercapacitors Based on SiC Nanowires Electrode and YSZ Electrolyte”, ACS Applied Materials and Interfaces 7, 26658–26665 (2015).
Gecko-inspired Synthetic Adhesives Geckos are known for their remarkable ability to vertically climb and stick to just about any surface. This is enabled by the hierarchical structures on their feet that range from stiff seta and spatula micro- and nano-structures to millimeter-scale lamellar arrays. Mimicking the multi-scale structure of the geckos has remained a challenge in the field. Utilizing the technique for parallel synthesis of silicon nanowires, master templates can be created with precisely controlled nanowire diameter, length, and density. Subsequent molding yield high-aspect-ratio polymer nanofiber arrays that exhibit high friction with low detachment force. The fibers can be molded with different types of polymers, e.g., polydimethylsiloxane, polypropylene, low- and high-density polyethylene. Furthermore, schemes are developed to mimic the additional levels of hierarchy into these nanostructures. Such adhesives have many potential applications, such as in biomedical and sports equipment, as well as for crawling micro-robots. Also, fabricating the fiber arrays with tailored geometry allows one to probe how the fundamental parameters of the nanofibers and the contacting substrate (e.g., fiber and substrate geometry, modulus, and surface energy) affect macroscopic properties like adhesion and friction. This effort provides broader insights for contact between non-ideal surfaces. Selected Publications H. Liu, J.-K. Choi, G. Zaghi, J. Zhang, C. Carraro, R. Maboudian, “Frictional characteristics of stiff, high aspect ratio microfiber arrays based on cyclic olefin polymers”, Journal of Adhesion Science and Technology, 1-11 (2016). Y. Tian, Z. Zhao, G. Zaghi, Y. Kim, D. Zhang, R. Maboudian, “Tuning the Friction Characteristics of Gecko-inspired PDMS Micropillar Array by Embedding Fe3O4 and SiO2 Particles”, ACS Applied Materials and Interfaces 7, 13232–13237 (2015). D.H. Lee, Y. Kim, G.S. Doerk, I. Laboriante, R. Maboudian, “Strategies for controlling Si nanowire formation during Au-assisted electroless etching”, Journal of Materials Chemistry, 21, 10359-10363 (2011); also featured in the Virtual Journal of Nanoscale Science and Technology, Vol. 24 (4), July 25, 2011.