Polybithiophene: a humidity sensor Omar E. Herrera 1 , David P. Wilkinson, 1 and Walter Mérida 1 1 Clean Energy Research Centre, University of British Columbia, Vancouver, BC, Canada V6T 1Z4 2 Institute for Fuel Cell Innovation, National Research Council Canada, Vancouver, BC, Canada V6T 1W5 The first conductive polymer was synthesized almost 150 years ago(1). However, intense research activity started until the late 1970s and early 1980s. Poly-thiophenes started to be synthesized and studied during this period(2). Poly-thiophene has primarily been used for photovoltaic devices. The interest in these polymers has increased because they are photoactive and they can be electrochemically deposited in smooth homogenous layers (3). Bithiophene has proven to be an excellent source for high quality poly-thiophene (4). The polymer is prepared by galvanostatic deposition on a (0.79375 mm diameter) gold surface at a current density of 1.0 mA/cm 2 using 0.5 M LiClO 4 + 0.1 M 2,2’-bithiophene in propylene carbonate as electrolyte. Samples were prepared using different deposition times (20 – 100 s). After synthesis the films are polarized at 200 mV vs Ag/AgCl, for the same amount of time used for the deposition process. After film preparation, samples are washed in propylene carbonate and then dried at 50 °C. A special multi-electrode glass cell, shown in Figure 1, was developed to coat 12 wires at a time with the polybithiophene (PBT) film. The temperature of the 12 working electrodes (T 1 ) can also be controlled while maintaining the temperature of the reference electrode at 25 °C (T 2 ). Figure 1. Cross-section of multi-electrode cell. The PBT electrodes can be at a different temperature (T 1 ) than the reference electrode (RE @ T 2 ). Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and potential versus time studies were carried out at different temperatures and proton concentrations (pH) in the cell shown in Figure 1. All of the experiments were carried out with no light. The CV, EIS and potential versus time studies for humidity were carried out in a cell where the dew point temperature and the gas temperatures can be controlled. The PBT electrode is in contact with a Nafion membrane that is contact with a reversible hydrogen electrode (RHE), as shown in Figure 2. The inner chamber can have a different gas than the outer chamber where the RHE is. The potential response to humidity on air, oxygen and hydrogen were recorded. Figure 2. Cross-section of humidity chamber cell. The RHE is in a hydrogen environment, while the PBT chamber can have different gases. PBT has specific response to pH, temperature and relative humidity. It can be used in different applications, such as fuel cells where proton concentration, temperature and relative humidity changes are dynamic. References 1. H. Letheby, Journal of the Chemical Society, 15, 161 (1862). 2. K. Kaneto, K. Yoshino and Y. Inuishi, Japanes Journal of Applied Science, 21, L567 (1982). 3. T. Morgenstern and U. König, Synthetic Metals, 67, 263 (1994). 4. E. Leguenza, R. Patyk, R. Mello, L. Micaroni, M. Koehler and I. Hümmelgen, Journal of Solid State Electrochemistry, 12, 213 (2008).