Novel stretchable fiber-shaped fluidic nanogenerators fabricated from carbonized lignin/thermoplastic polyurethane

https://doi.org/10.1016/j.indcrop.2022.115240Get rights and content

\Highlights

  • A new stretchable carbonized lignin/thermoplastic polyurethane FFNG was built.

  • A high direct current (DC) voltage was achieved up to 420 mV.

  • A self powered fiber-shaped wave sensor was developed.

Abstract

Harvesting energy from water flow using fiber-shaped fluidic nanogenerators (FFNGs) based on liquid-solid contact electrification has practical significance. Challenges remain in the fabrication of conformal FFNGs with favorable durability and a large strain range. Herein, a robust, flexible, and stretchable FFNG is fabricated using carbonized lignin and thermoplastic polyurethane via wet-spun approach. A maximum output direct current voltage of 420 mV is generated when the saline solution flows over a 6-cm-long FFNG. The output voltage of the FFNG shows excellent stability and repeatability in multiple cyclic tensile tests. Furthermore, the excellent mechanical properties and high stretchability of FFNG enable it to be woven into fabric, proving its tremendous potential for use in conformal electronics. The robust FFNG can also act as a self-powered wave sensor, which provides basic information on the wave conditions.

Introduction

Oceans cover approximately 70 % of the earth's surface and approximately 44 % of the world's population lives within 150 km of the coastline. It has become inevitable for humans to harvest blue energy from the sea to meet the growing global energy needs (Ahmed et al., 2017, Urban, 2017, Wang et al., 2019a). Hydropower is one of the most common forms for electricity generation, however, it requires large turbines and sophisticated machinery, and specific sites with large water level differences for efficient operation. As irregular and low-frequency mechanical energy sources, such as raindrops, ocean waves, and tides cannot be harnessed efficiently with hydropower technology (Poff et al., 2007, Wang, 2017, Liu et al., 2021), there is a pressing interest in designing novel, efficient, and miniaturized energy systems to overcome these limitations.

With the advances in nanomaterials and nanotechnologies, nanogenerators based on interactions at the liquid-solid interface can perfectly mitigate these limitations (Wang and Li, 2021, Xu et al., 2021, Zhang et al., 2021, Saxena and Shukla, 2021). In the last decade, carbon-based nanomaterials have attracted significant attention as they are capable of generating instantaneous direct current and are available in different forms, such as powder, tube, fiber, composite, 2D thin film, and 3D foam (Ding et al., 2017, Liu et al., 2018b, Zhang et al., 2017). For instance, few millivolts can be produced by moving a droplet of NaCl solution over a strip of monolayer graphene (Yin et al., 2014). A peak voltage of 30 mV was produced when 1 M NaCl aqueous solution flowed over a MWCNT array at a speed of 8.3 cm s−1(Liu et al., 2007). Moreover, evaporation from centimeter-sized carbon black sheets can reliably generate sustained voltages of up to 1 V under ambient conditions (Xue et al., 2017).

To date, inflexible rigid plates are the typical form of fluidic nanogenerators. However, the rigidity of these widely explored bulky energy conversion devices has limited their conformity to mostly irregular and soft surfaces. Although some thin-film power systems have been designed to achieve flexible or stretchable energy devices, the film structure cannot be twisted freely or deformed extensively (Kwak et al., 2016, Tian et al., 2020, Jia et al., 2021). To this end, several efforts have been made to fabricate fiber-shaped fluidic nanogenerators (FFNGs) (Xu et al., 2019, Xu et al., 2017, Yang et al., 2020). Carbon fibers are stiff and thus cannot be stretched easily. Similarly, graphene and carbon nanotube (CNT) fibers cannot be used on a large scale because of their high price (Fang et al., 2018). Consequently, the development of low-cost, robust, flexible, and stretchable fiber-shaped nanogenerators remains a challenge.

Owing to its carbon-rich phenolic structure and ubiquity in nature, lignin can be considered as a promising alternative precursor for biobased carbonaceous powder (Kleinhans and Salmen, 2016, Poursorkhabi et al., 2020). It is derived as a byproduct of the pulping process in the paper industry and has a significantly high carbon content (60–65 %). Carbonaceous powder from lignin and lignin-rich biomasses has high carbon content and high yields (Correa et al., 2017). According to the literature, the cost of lignin is $ 1.1 kg−1, excluding the carbonization process, which can increase the cost to $ 6.3 kg−1(Fang et al., 2017). Due to low cost, carbonized lignin has been studied as a potentially sustainable alternative for contemporary conductive materials in energy storage and conversion devices (Geng et al., 2021, Wang et al., 2019b).

In this study, we fabricated a conductive fiber based on thermoplastic polyurethane(TPU) and carbonized lignin (CL) to achieve a practical FFNG that is lightweight, flexible, and stretchable. TPU was selected as the matrix owing to its excellent flexibility and plasticity (Wang et al., 2018a, Wang et al., 2018b). The composite fiber was fabricated using a simple and cost-efficient wet-spun technique, which could be easily scaled up for large-scale production. When multiple FFNGs were subjected to a flowing NaCl aqueous solution, instantaneous high voltage and current were achieved. With the optimized parameters, a 6-cm long FFNG could generate a direct current(DC) voltage of up to 420 mV. The reported resources and methods pave the way towards developing cost-effective and stretchable FFNGs that can harvest the blue energy.

Section snippets

Materials

Polyester-based thermoplastic polyurethane (TPU) (Elastollan 1185 A, BASF) and dimethylformamide (DMF)(99.5 % AR, Aladdin) were used as received. Enzymatic lignin was obtained from Shandong Longli Biotechnology Co.Ltd., China and DI water (Milli-Q, Merck Millipore) was used in all experiments.

Preparation of carbonized lignin

The enzymatic lignin was purified prior to carbonization, lignin was successively soaked in 4 wt % NaOH and 10 wt % HCl aqueous solutions, followed by washing with a copious amount of DI water until the

Design and characterization of FFNG

A schematic diagram of the FFNG and the experimental configuration is shown in Fig. 1a.The TPU/CL composite fibers were fabricated using the wet-spun technique (Fig. S1), which enabled the preparation of continuous fibers with varying CL content. After drying, the two ends of the fiber were connected to copper wires and painted with hot-melt adhesives. The fiber was then fixed at the center of a transparent plastic pipe, as shown in Fig. 1a. To generate the electricity, a NaCl solution was

Conclusions

In this work, a TPU/CL composite-based FFNG was fabricated, displaying an interesting DC electrical output. The dependence of the output voltage of the FFNG on the flow rate and concentration of NaCl solution, FFNG length, and CL content were systematically studied. With optimization, a 6-cm-long FFNG could deliver an output voltage of up to 420 mV. Additionally, the FFNG exhibited excellent voltage stability and repeatability in multiple tensile cycle tests. The novel composite fibers were

CRediT authorship contribution statement

Jiawen Gao: Investigation, Writing – original draft. Hanxiao Zhang: Formal analysis. Qiannan Zhang: Investigation. Siqi Li: Investigation. Bin Luo: Investigation. Jiulong Sha: Conceptualization, Writing – review & editing, Supervision. Hongbin Liu: Writing – review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This research was supported by grants from the Natural Science Foundation of China (22108047), China and the Guangxi Natural Science Foundation of China (2019GXNSFAA185010), China.

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