Core-shell fiber wet gas generator via synergistic complex coacervation and built-in potential

First author: Guangtao Zan, Wei Jiang, HoYeon Kim

Corresponding author: Cheolmin Park

Corresponding Units: Yonsei University, Korea Institute of Science and Technology (KIST)

DOI: 10.1038/s41467-024-54442-4

Background

The development of self-powered flexible wearable electronic devices has attracted great attention in the development of human-machine interface technologies. As a result, various complex generators capable of harvesting ambient energy have been designed, including triboelectric/piezoelectric-based nanogenerators, thermoelectric generators, solar cells, and moisture-driven generators (MEGs). Among them, MEGs are promising because their operation is based on the ubiquitous presence of moisture, which makes them potentially suitable for self-powered electronics when certain requirements are met, such as high harvesting performance comparable to other alternatives, excellent mechanical elasticity, breathability, and biocompatibility. Although high-performance MEGs have been extensively studied by exploring new materials with optimized device structures (e.g., graphene oxide, carbon dots, hydrogels, proteins, aerogels, and polyelectrolytes), their energy harvesting performance remains subpar, necessitating the development of new material strategies to improve performance. Previous studies have shown that MEGs produce relatively low current densities, which is usually caused by the limited number of mobile ions that preferentially dissociate on the energy-generating material and their long transport paths and slow diffusion rates. To address this fundamental challenge in MEG, we envision that the phase-separated complex coacervation of two oppositely charged polyelectrolytes driven by enthalpy and entropy is considered to be one of the most effective microencapsulation technologies and is widely used in pharmaceutical, food, agriculture, and textile industries. This technology is promising because a large number of additional mobile ions can be easily generated during the complex coacervation process. In addition, the phase separation associated with dense coacervation increases the free volume in the system, enabling the rapid diffusion of ions. To further facilitate the diffusion of ions, a core-shell structured fiber-based MEG is proposed, which has a mechanically flexible electrode core and coacervate shell, which also makes the MEG resistant to various mechanical deformations such as bending, folding, rolling, and twisting.

Highlights of this article

1. This work proposes a novel composite coacervation and built-in potential strategy for developing high-performance uniaxial MEG, whose core is poly(3,4-ethylenedioxythiophene) (PEDOT) with built-in charge potential and the gel shell is composed of poly(diallyldimethylammonium chloride) (PDDA) and sodium alginate (NaAlg) coacervates.

2. The uniaxial fiber-based MEG exhibited breakthrough performance, achieving an output voltage of up to 0.8 V, a maximum current density of 1.05 mA/cm ^2, and a power density of 184 μW/cm ²  at 20% relative humidity.

3. The mechanical strength of the PEDOT nanoribbon substrate is guaranteed, and the performance will not be degraded even after 100,000 folding cycles, making it suitable for self-powered human-computer interaction sensors and synapses.

4. The first MEG-synapse self-powered device was constructed, and fiber-based MEG successfully operated synaptic memristors, thereby simulating autonomous human synapses connected to fiber neurons.

Figure. Design and performance of fiber-based MEG.

A Schematic diagram of the synergistic strategy of complex coagulation and built-in potential. b Output voltage, c current density, d voltage and current density during resistance change, e corresponding power density of fiber-based MEG at 20% RH. f Performance of fiber-based MEG and previously reported MEG. g Comparative radar plot of representative MEG.

Figure. Self-powered device demonstration.

A Traditional Morse telegraph model and code. b Working principle of information transmission device based on fiber-optic MEG. c Transmission of information through Morse code using the change of current signal generated by fiber-optic MEG. d Fibers integrated into systems with different shapes: knitted fabric, five-pointed star shape, spider web design, and fibers with the word "NPL" embedded in gauze. e Schematic diagram of biological synapses induced by action potentials and artificial synaptic devices powered by MEG potentials. f Long-term potentiation (LTP) curves obtained at different pulse durations using one MEG unit. g, h LTP and long-term depression (LTD) curves obtained using one MEG unit. i, Graph of LTP and LTD versus the number of pulses powered by one MEG unit.