Effect of surface coating of microcrystalline cellulose by imidazole molecules on proton conductivity I. Smolarkiewicz a,b , A. Rachocki a , K. Pogorzelec-Glaser a , P. Lawniczak a , R. Pankiewicz c , J. Tritt-Goc a,⇑ a Institute of Molecular Physics, Polish Academy of Sciences, M. Smoluchowskiego 17, 60-179 Poznan ´, Poland b NanoBioMedical Centre, Adam Mickiewicz University in Poznan ´, Umultowska 85, 61-614 Poznan ´, Poland c Faculty of Chemistry, Adam Mickiewicz University in Poznan ´, Umultowska 89b, 61-614 Poznan ´, Poland article info Article history: Received 13 January 2016 Received in revised form 25 February 2016 Accepted 20 March 2016 Available online 21 March 2016 Keywords: Microcrystalline cellulose Imidazole Polymer-matrix composite Proton conductivity Impedance spectroscopy abstract The proton conductivity properties of a newly synthetized proton-conducting composite (Cell-Im) composed of the microcrystalline cellulose grains (Cell) coated with different amount of imidazole molecules (Im) have been investigated. For the composite with the highest concentration of Im (on average 1 Im molecules is bonded to approximately 5.44 glucose rings; 5Cell-Im), the increase in the maximum conductivity by nearly 3 orders of magnitude with respect to that of neat cellulose, and the extension of the temperature range application up to 160 °C was evidenced in anhydrous conditions. Under these conditions two contributions to the overall conductivity of 5Cell-Im were recognized in the temperature range of 60–150 °C. They are related to the imidazole layers at grain surfaces and intergrain contacts, respectively. The interior of the cellulose grains is treated as a nearly ‘‘perfect” dielectric with a negligible contribution to conductivity. The lowering of the Im concentration at the cellulose grain surface leads to decreasing of the surface conductivity. A characteristic phase transition from proton conductivity state to non-conductivity one with typical percolation threshold is well documented. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction The need to design ‘‘water-free” electrolytes for application in various electrochemical devices (e.g., fuel cells, batteries, sensors, etc.) forces the search for new materials which exhibit the desired electrical properties in anhydrous conditions. Among different advanced materials some hydrophilic biopolymers as chitin, chitosan, or cellulose (and its derivatives) func- tionalized to replace water by nitrogen-containing heterocycles such as imidazole, benzimidazole, or triazole are especially promising [1–7]. The heterocycles are attractive due to their amphoteric nature (the structure contains both a proton donor (NH) and a proton acceptor (N:) side), and high thermal stability [6,7]. Their melting points are higher than water, which makes them interesting candidates for supporting proton conductivity at intermediate temperature. Moreover, the nitrogen-containing heterocycles molecules form hydrogen bonded networks similar to that found in water, and possess transport properties comparable to that of water with proton transfer occurring via Grotthuss mechanism, also called ‘‘structural diffusion” [8,9]. Proton transfer requires structural diffusion because heterocyclic molecules, e.g. imidazole, are bonded to the polymer backbone. Proton hopping between adjusted imidazole molecules involves some configuration http://dx.doi.org/10.1016/j.eurpolymj.2016.03.026 0014-3057/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: jtg@ifmpan.poznan.pl (J. Tritt-Goc). European Polymer Journal 78 (2016) 186–194 Contents lists available at ScienceDirect European Polymer Journal journal homepage: www.elsevier.com/locate/europolj