Electrochemical and electromechanical properties of high-performance polymer actuators containing vapor grown carbon nanofiber and metal oxide

The effects of metal oxide and an ionic liquid (IL) on the electrochemical and electromechanical properties of poly(vinylidene fluoride-co-hexafluoropropylene) actuators were investigated using a vapor grown carbon nanofiber (VGCF)-IL gel electrode containing metal oxide, formed without using ultrasonication. The double-layer capacitance of the VGCF electrode containing MnO2 was larger than that of electrodes containing either only VGCF or RuO2/VGCF. A MnO2/VGCF electrode containing 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI[BF4]) gave the largest capacitance of those tested. The VGCF polymer actuator containing MnO2 surpassed the performance, in terms of strain and maximum generated stress, of actuators prepared with VGCF only, RuO2/VGCF, or single-wall carbon nanotubes (SWCNTs) only. The MnO2/VGCF actuator containing EMI bis(trifluoromethanesulfonyl)imide (EMI[TFSI]) gave the largest strain and the MnO2/VGCF actuator containing EMI[BF4] gave the largest maximum generated stress. The capacitance of the MnO2/VGCF/IL electrode and the strain for the MnO2/VGCF/IL actuator contribute to the pseudocapacitance. Both VGCF and MnO2 are necessary to produce actuators with large and rapid responses that surpass the performance of polymer actuators containing only VGCF, RuO2/VGCF, and only SWCNTs. Furthermore, the frequency dependence of the displacement response of the RuO2 or MnO2/VGCF polymer actuator was successfully simulated using an electrochemical kinetic model. The result for simulation of the electromechanical response of the RuO2 or MnO2/VGCF actuators provided the strain at a limit of low frequency and the time constant for the simulation.