Wider Potential Windows of Cellulose Multiwall Carbon Nanotube Fibers Leading to Qualitative Multifunctional Changes in an Organic Electrolyte

Abstract

The trend across the whole of society is to focus on natural and/or biodegradable materials such as cellulose (Cell) over synthetic polymers. Among other usage scenarios, Cell can be combined with electroactive components such as multiwall carbon nanotubes (CNT) to form composites, such as Cell-CNT fibers, for applications in actuators, sensors, and energy storage devices. In this work, we aim to show that by changing the potential window, qualitative multifunctionality of the composites can be invoked, in both electromechanical response as well as energy storage capability. Cell-CNT fibers were investigated in different potential ranges (0.8 V to −0.3 V, 0.55 V to −0.8 V, 1 V to −0.8 V, and 1.5 V to −0.8 V), revealing the transfer from cation-active to anion-active as the potential window shifted towards more positive potentials. Moreover, increasing the driving frequency also shifts the mode from cation- to anion-active. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy were conducted to determine the ion species participating in charge compensation under different conditions.

Cation-Selective Actuator–Sensor Response of Microcrystalline Cellulose Multi-Walled Carbon Nanotubes of Different Electrolytes Using Propylene Carbonate Solvent

“…Previous research [11] discovered that the potential range is qualitative in viewing which actuation direction is preferred. The actuation direction, either expansion at positive charging or negative charging, considering which ions lead to forming the electrical double layer, has been shown in MCNT yarns, also depending on the size of applied ions [24].…”

“…After 12 h stirring at 85 • C, the MCNTs (MCNT, 50 wt.%) were added to the suspension and ultrasonicated at room temperature for 30 min. The mixture was then placed in a syringe (760 µm inner diameter) and extruded in anti-solvent (Milli-Q+, Tallinn, Estonia) using a procedure that was shown in detail in a previous study [11]. To remove excess EMIMCl, the MC-MCNT fibers were washed with ethanol several times and then dried in an oven at 40 • C at 2 mbar.…”

“…Such a cellulose IL MCNT suspension can be formed in fiber through electrospinning [8] or obtained via extrusion, forming MC-MCNT fiber in anti-solvent (water) [9], as was carried out in this work. Recent research using MC-MCNT fiber in aqueous [10] or organic electrolytes [11] revealed that the chosen potential range plays a role in which actuation direction, either expansion at negative charging or expansion at positive charging, is obtained.…”

Sustainability of Multiwall Carbon Nanotube Fibers and Their Cellulose Composite

“…In the case of Cell-CNT fibers, a more complex mechanism of charging/discharging induced linear actuation exists, despite the fibers' generally compact structure due to cellulose covering most of the CNT materials (Figure 1a) [32]. Besides which solvent, aqueous or organic, is chosen, the choice of the applied potential range plays a vital role [30]. The TFSI − anions are incorporated in the Cell-CNT fiber, and the chloride anions of EMIMCl residue are still inside the Cell-CNT fiber (fluoride and chloride elements are shown in EDX in Figure 2c).…”

“…Comparison to other actuator work is often tricky due to different actuation conditions. For example, if the actuators are applied with different CNT materials (modified or unmodified), electrolytes, solvents, and potential ranges [30], as well as different procedures of CNT in composites, coatings, yarns, and fibers, this may lead to different outcomes.…”