New proton conducting membrane based on bacterial cellulose/polyaniline nanocomposite film impregnated with guanidinium-based ionic liquid

New protic ionic liquid N-butylguanidinium tetrafluoroborate (BG-BF4) has been synthesized by single-step method. The ionic liquid is thermally stable to at least 300 degrees C and has ionic conductivity value of 8.10(-3) S/cm at room temperature increasing to 0.18 S/cm at 180 degrees C. To develop a new proton conducting membrane, the nano-fibrillar matrix of bacterial cellulose (BC) has been impregnated with BG-BF4. The composite BC/BG-BF4 membrane containing 80 wt% of ionic liquid was found to have tensile strength of 35 MPa and ionic conductivity of 4.5.10(-4) S/cm at 180 degrees C. The high saturation of BC with protic ionic liquid to 95 wt% allowed obtain composite membrane with reduced tensile strength of 6 MPa but excellent ionic conductivity of 5.2.10(-2) S/cm at 180 degrees C. The deposition of polyaniline (PANI, emeraldine base) into BC matrix by oxidative polymerization of aniline on the surface of cellulose nanofibrils was found to improve the ionic conductivity of BC/BG-BF4 system significantly, reaching the value of 4,10(-3) S/cm at 180 degrees C for cellulose film containing 80 wt% of ionic liquid. According to results of dynamical mechanical analysis (DMA), both BC/BG-BF4 and BC/PANI/BG-BF4 composites keep excellent storage modulus values at 180 degrees C (1000 MPa and 835 MPa, respectively). Due to the excellent holding capacity of BC matrix to ionic liquid, as well as good thermal and mechanical properties of BC/BG-BF4 composite it can be promising material for the fabrication of proton conducting membranes for fuel cells operating at elevated temperatures in water free conditions. (C) 2018 Elsevier Ltd. All rights reserved.