Coffee-Driven Green Activation of Cellulose and Its Use for All-Paper Flexible Supercapacitors

Abstract

Cellulose, which is one of the most-abundant and -renewable natural resources, has been extensively explored as an alternative substance for electrode materials such as activated carbons. Here, we demonstrate a new class of coffee-mediated green activation of cellulose as a new environmentally benign chemical-activation strategy and its potential use for all-paper flexible supercapacitors. A piece of paper towel is soaked in espresso coffee (acting as a natural activating agent) and then pyrolyzed to yield paper-derived activated carbons (denoted as "EK-ACs"). Potassium ions (K), a core ingredient of espresso, play a viable role in facilitating pyrolysis kinetics and also in achieving a well-developed microporous structure in the EK-ACs. As a result, the EK-ACs show significant improvement in specific capacitance (131 F g at a scan rate of 1.0 mV s) over control ACs (64 F g) obtained from the carbonization of a pristine paper towel. All-paper flexible supercapacitors are fabricated by assembling EK-ACs/carbon nanotube mixture-embedded paper towels (as electrodes), poly(vinyl alcohol)/KOH mixture-impregnated paper towels (as electrolytes), and polydimethylsiloxane-infiltrated paper towels (as packaging substances). The introduction of the EK-ACs (as an electrode material) and the paper towel (as a deformable and compliant substrate) enables the resulting all-paper supercapacitor to provide reliable and sustainable cell performance as well as exceptional mechanical flexibility. Notably, no appreciable loss in the cell capacitance is observed after repeated bending (over 5000 cycles) or multiple folding. The coffee-mediated green activation of cellulose and the resultant all-paper flexible supercapacitors open new material and system opportunities for eco-friendly high-performance flexible power sources.

Large area few-layer graphene with scalable preparation from waste biomass for high-performance supercapacitor

“…2d , inset) reveals achievement of mesopores (2.1–5.4 nm) during exfoliation. Microporous substances with an enhanced surface area is ideal for elevated capacitance and power density in aqueous electrolyte because of high conductivity and smaller ionic size 62 . But to explore its potential in the organic electrolyte, it is necessary to have a reasonable mesopore volume and their good interconnectivity for the electrolyte ions to effectively realize all the available surface area of the carbon framework 63 , 64 .…”

“…4e ), which corresponds to the (002) plane of few-layered graphene nanosheets. Selected area electron diffraction (SAED) analysis reveals the presence of a hexagonal lattice of crystalline graphene-like sheets with long-range order 62 . As can be observed from the diffraction pattern in Fig.…”

Flexible Supercapacitors: A Materials Perspective

“…They can also be formed by ink-jet printing or spin-coating the carbon materials on flexible plastic or paper substrates. Paper forms a highly suitable substrate due to its high porosity and surface area, but large pore sizes can cause the carbon nanostructures to penetrate into the substrate (Lee et al, 2017) (Pushparaj et al, 2007). Applying polyvinylidene fluoride coating on the substrate has been used as a facile pre-treatment method to facilitate maximum adhesion of carbon electrode materials to the porous paper substrate while maintaining the electrical conductivity.…”

Facile, Scalable, Eco-Friendly Fabrication of High-Performance Flexible All-Solid-State Supercapacitors

“…In recent years, increased scientific interest has turned toward the use of cellulose fiber (CF)—an abundant, renewable, recyclable, and biodegradable material—as a substrate for the preparation of freestanding electrodes [15,16,17,18,19]. An additional attraction of CF is that its large number of surface functional groups enables the fibers to bind with electrochemically active materials, e.g., carbon nanotubes (CNTs) [20,21], graphene/graphite [5,13,22,23,24], conducting polymers [16,17,20,22,25,26], and metal ions and oxides [18,27,28] to form freestanding electrodes.…”