Superior Electrochemical Platforms based on Polymer Carbon Nanotube Composite Electrodes Suriya Ounnunkad 1 , Andrew I. Minett 1 , Barry D. Fleming 2 , Chong-Yong Lee 2 , Alan M. Bond 2 , Gordon G. Wallace 1 1 ARC Centre of Excellence for Electromaterials Science, Intelligent Polymer Research Institute, University of Wollongong Innovation Campus, AIIM Building, Squires Way, Fairy Meadow, NSW 2519, Australia 2 School of Chemistry, Monash University, Clayton, Victoria 3800, Australia suriyacmu@yahoo.com, aminett@uow.edu.au, Alan.Bond@sci.monash.edu.au, gwallace@uow.edu.au Abstract—Putting insulating polymers into a highly conductive single-walled carbon nanotube paper leads to excellent electrochemical performance; fast redox reactions and high signal to background noise ratio. The ability of such composites to serve as superior electrochemical platforms was investigated by using DC and AC cyclic voltammetry. The electrochemical platforms show benefits in sensing applications with fast signal generation and low limits of detection. Keywords-Buckypaper; intercalation; cyclic voltammetry; AC voltammetry I. INTRODUCTION Over the last two decades, carbon nanotubes (CNTs) have been intensively investigated in various architectures for use as electrochemical sensing platforms [1-4]. These electrochemical platforms can be directly used as electrodes or functionalised with active sensing elements for detection applications with good stability and selectivity [1-6]. Various electrode architectures can be made from CNT soot, such as CNT paste electrodes[9], screen-printed electrodes [10], fibres [11], papers [12], or biogels [13]. CNT structuring and patterning such as aligned CNTs [8] and CNT Nanowebs [14] can be achieved by careful design of chemical vapour deposition processes. CNT papers or Buckypapers (BPs) have a unique character with very high capacitance contributed by their high electro-active surface areas and high porosity, forming large double layer capacitive films on surfaces. For these types of architectures, it is much more difficult to use them as sensing electrodes since they suffer from very large background currents due to this capacitive charging [15]. With low capacitive charging, ultrathin CNT BPs sitting on membranes and their composites also offer enhanced performance as sensing platforms for chemical and biochemical sensors [16] while nafion-CNT composite BPs revealed an ability to oxidize NADH, benefits for glucose biosensors [17]. The high contribution from this capacitive charging current masks the redox process in electrochemical detection techniques; ie: lowering the signal to background ratio. The fabrication of sensing platforms from BPs with good sensitivity and selectivity is a challenging issue in electroanalysis and is the focus of this report. In this present work, an inverse modification process which uses insulating polymers to improve the electrochemical sensing efficiencies of highly capacitive CNT architectures is reported. This is in contrast to the usual route of embedding CNTs into polymer composites. This process results in a novel CNT BP nanocomposite electrode platform via the intercalation of organic, non-water soluble, non-conducting polymers, which has the added benefit of providing good mechanical properties and stability for practical applications. The structure surprisingly provides an improvement in the signal to noise ratio in terms of Faradaic to background charging current ratio. There have been only three intercalated organic polymers identified so far, which have a very low capacitance. These are; poly(styrene-β-isobutylene-β-styrene) (SIBS), polyisobutylene (PIB) and polystyrene (PS). The polymers effectively decrease the total free volume available by blocking the interstitial, interbundle and/or intertube voids in the architecture (see Fig. 1). They additionally provide an electrode surface that is predominantly more hydrophobic in nature to the raw BP, which reduces electrolyte access into the pore structure reducing the formation of double layer capacitive films. In this study, we use a combination of DC and AC cyclic voltammetry to evaluate the properties of these prepared electrode platforms. Fourier Transformed (FT-AC) voltammetry is a powerful technique that provides information on electron transfer rates and kinetics in a single experiment [18]. II. EXPERIMENTAL DETAILS Free-standing single-walled carbon nanotube (SWCNT) mats were prepared by a vacuum-assisted filtration of well- dispersed SWCNT solution [12]. Triton-X100 was used as a dispersant. After SWCNT paper settled on a 0.22-µm hydrophobic PVDF membrane, the paper was washed with Milli-Q water several times to remove non-interacting Triton- X100 and followed with ethanol. The SWCNT membrane was peeled off from PVDF membrane. It was left for drying in a room temperature. For polymer-SWCNT composite BP, the three different insulating polymers each was intercalated by soaking the raw BP in a 5%w/v polymer solution at desired periods. After that, intercalated BP was carefully rinsed with the solvent and let dry at room temperature. The composite Buckyelectrodes (BEs) were used as working electrodes in a three-electrode electrochemical cell with a platinum mesh auxiliary electrode and a Ag/AgCl (3M NaCl) reference