Flexible robust binder-free carbon nanotube membranes for solid state and microcapacitor application

We present a liquid phase post synthesis self-assemble protocol that transforms trillions of carbon nanotubes (CNTs) in powder form into densely packed flexible, robust and binder-free macroscopic membranes with a hierarchical pore structure. We employ charge transfer engineering to spontaneously disperse the CNTs in a liquid medium. The processing protocol has limited or no impact on the intrinsic properties of the CNTs. As the thickness of the CNT membrane is increased, we observed a gradual transition from high flexibility to buckling and brittleness in the flexural properties of the membranes. The binder-free CNT membranes have bulk mass density greater than that of water (1.0 g cm(-3)). We correlate the mass of the CNTs in the membrane to the thickness of the membrane and obtained a bulk mass density of similar to 1.11 g cm(-3) +/- 0.03 g cm(-3). We demonstrate the use of the CNT membranes as electrode in a pristine and oxidized single/stacked solid-state capacitor as well as pristine interdigitated microcapacitor that show time constant of similar to 32 ms with no degradation in performance even after 10 000 cycles. The capacitors show very good temperature dependence over a wide range of temperatures with good cycling performance up to 90 degrees C. The specific capacitance of the pseudocapacitive CNT electrode at room temperature was 72 F g(-1) and increased to 100 F g(-1) at 70 degrees C. The leakage current of bipolar stacked solid state capacitor was similar to 100 nA cm(-2) at 2.5 V when held for 72 h.