MnO₂/PtNP Embedded Wet‐Spun Fiber Supercapacitors

Abstract

Here, we demonstrate continuously producible wet-spun supercapacitors having an embedded structure that consists of carbon nanotube (CNT), manganese dioxide (MnO 2 ), and platinum nanoparticle (PtNP). Amorphous MnO 2 , a promising pseudocapacitive material, was added to improve electrochemical performance to an average 20 times higher than wet-spun CNT fiber. However, MnO 2 has low conductivity and limited solidstate charge, with the result that electrochemical performance decreases induced by rate-capability decrease. Therefore, the rate capability was improved up to 60% and specific capacitance was obtained by adding PtNP to enhance ion accessibility and decrease equivalent series resistance (ESR). Furthermore, all-solidstate symmetric supercapacitors provide a capacitance of 53.1 mF cm −2 at 2 mV s −1 using poly(vinyl alcohol) (PVA)/LiCl gel electrolyte. Our MnO 2 /PtNP embedded wet-spun supercapacitor can be produced in a simple and easy one-step process compared with other methods that require post-treatment. Unlike existing research on carbon-based and fiber-type wet-spun supercapacitors, [18][19][20][21][22]25] it is the first time for fabrication by adding a pseudocapacitive material. In addition, it shows the possibility of fabricating a supercapacitor using various active materials besides MnO 2 used in the paper. Figure 1a shows a schematic image of the fabrication process of the wet-spun fiber-type supercapacitor. Other methods require complex thermal and electrochemical processes, but our wet-spinning method is simple and easily makes fiber-type supercapacitors including pseudocapacitive material without post-treatment, like hydrogen iodide treatment. First, a mixed solution of CNT powder, MnO 2 power, PtNP, and water fills a syringe with gauge inner diameter of 0.5 mm. Then, pushing the piston with constant speed makes wet-spun fiber into a spinning coagulation bath of PVA/water. MnO 2 is a transition metal dioxide that is a promising pseudocapacitive material. CNT is a conductive skeleton of fiber with good mechanical properties and provides alignment from its aspect ratio. CNT forms a conductive electrode while wrapping the MnO 2 . In addition, it is an environmentally friendly and low-cost material because of its abundance in nature, but it has low electrical conductivity (≈10 −6 S m −1 ). [26] Continuously fabricable wet-spun fiber supercapacitor has an issue of electrical conductivity because resistance is proportional to length. To overcome this Fiber-shaped microsupercapacitors that have small volume and high flexibility are particularly needed due to the sudden high demand for appropriate power sources for wearable electronics, smart textiles, and microrobotics. For commercialization of fiber supercapacitors, an economical and mass-producible fabrication process is required. However, most wet-spun fiber supercapacitors are graphene-based electrodes that require complicated and dangerous post-treatment, such as using heat and chemical reaction. Here, continuous wet-spun fiber supercapacitors ...