Revolutionizing Neurotechnology: Stretchable Electrode with Cerebral Cortex-Like Structure, Metal-Like Conductivity, and Rubber-Like Stretchability
Professor Cho Jin-han’s group of the Department of Chemical and Biological Engineering in the College of Engineering has successfully developed a stretchable electrode with a cerebral cortex-like surface, exhibiting high electrical conductivity and a large surface area as well as mechanical stability. The research group employed the manufactured stretchable electrode to develop a high-performance triboelectric nanogenerator.
*Triboelectric nanogenerator: A device for converting mechanical energy to electrical energy based on the charging of objects by the friction therebetween and the principle of electrostatic induction.
The results of the research were published online in Nano Energy (IF = 17.6), a renowned journal in the field of nanoscience and nanotechnology, on August 26.
The development of next-generation flexible electronic devices such as wearable electronics and electronic skin requires the preparation of stretchable electrodes of high electric conductivity and large surface area as well as good mechanical stability. For this, research has been conducted on the fabrication of stretchable electrodes by simply coating an elastomer material possessing excellent mechanical properties with a conductive material or by performing vacuum deposition.
However, in this situation conventional conductive materials inherently have low electric conductivity and high contact resistance due to the insulating materials surrounding the particle surface. In addition, there is the problem that the weak binding force between the conductive materials and the elastomer causes easy desorption of the conductive materials from the electrode surface. Therefore, the fabrication of an electrode featuring high conductivity and high mechanical stability is required for the commercialization of stretchable electrodes.
To this end, Professor Cho’s group successfully developed an electrode that has a cerebral cortex-like surface microstructure and exhibits metal-like electrical conductivity and elastomer-like stretchability (Fig. 1). The researchers induced a strong chemical bonding among the metal nanoparticles on an elastomer interface swollen in an organic solvent. Afterwards, they induced considerable shrinkage in an alcohol to fabricate an elastic conductor of a cerebral cortex-like wrinkled structure. Then, they coated the fabricated conductor with a very thin nickel layer through electroplating.
The manufactured electrode has a metal-like conductivity, and, due to the microstructure created during the metal nanoparticle assembly, the electrode has a surface area that is about 12 times as large as a flat electrode without a microstructure. Since a larger electrode surface area provides a wider contact area, the manufactured electrode can exhibit high performance when applied to a triboelectric nanogenerator.
Furthermore, although the electrode was electroplated with nickel, of which the mechanical properties are relatively poor, the manufactured electrode maintained the elastomer’s high flexibility and stretchability, exhibiting a very high mechanical stability compared to the conventional commercially available electrodes manufactured by sputtering.*
*Sputtering: A method of vacuum deposition. Ionized gas molecules are accelerated in a vacuum state to collide with a metal target to eject metal atoms, which coat a substrate to form a thin metal film.
The electrode retained conductivity and the surface microstructure remained unchanged even after the electrode surface was compressed by a strong force more than 20,000 times, exhibiting excellent mechanical properties. Based on the large surface area and the excellent mechanical properties of the manufactured electrode, the research group was able to generate energy at a high-power density by applying the electrode to a triboelectric nanogenerator.
Park Moon-kyu, who led the research, emphasized, “The elastomer-based electrode that we propose is a platform technology applicable to all areas where stretchable electrodes of large surface area are required, because it can be coated with various active materials.” Furthermore, Professor Cho commented, “We have overcome the limitations of both mechanical stability and electrical conductivity, which used to be obstacles to the commercialization of stretchable electrodes. Therefore, we will be able to make great contributions to the development of next-generation electronic devices.”