Elastic Cu@Ppy Sponge for Hybrid Device with Energy Conversion and Storage
Authors: Li Zhe , Li Zhou 
Published: February 2020

Sponge is a kind of material which features amounts of micron-to-millimeter sized pores, whilst displays intriguing mechanic properties, such as foldable, rollable, and shapeable. The modified sponges have been widely applied in energy storage, sensors, photocatalysis and other fields, to name a few. As one kind of sponge, PDMS-based sponges possess numerous advantages, which hold great potential in fabricating flexible electronics, such as sensors. Firstly, the PDMS is low-cost, simple conduction and accessible in ordinary laboratories. Secondly, the PDMS has strong adhesiveness and chemical inertly. Moreover, the PDMS sponge is readily modifiable and tailorable for variable applications.
Particularly, with the fast development of energy harvesting technique, the triboelectric nanogenerator (TENG), which is a powerful technique with low-cost, high efficiency, and environmentally friendly features, has been used to convert almost all forms of mechanical energy in our living/working environment into electricity. Recently, due to the specialities of PDMS, reports on the whole PDMS modification instead of only surface functionalization were documented, such as PDMS-based composites formation and filling with dielectric material, in which affirmed the importance of whole PDMS modification on improving the TENG output.
Flexible supercapacitors (SCs) are distinctly important because of their higher power density, longer cycle life, and higher charge/discharge rates as compared with those of traditional batteries. Moreover, the flexible supercapacitors may adjust their conformations to accommodate the environmental variations while without remarkable loss in their electrochemical performance. In order to fabricate flexible supercapacitors, strain-tolerant electrodes with outstanding mechanical elasticity, high capacitance, and good durability are largely unmet and still intensely pursued.
PPy, as an electroconductive polymer (ECP) with high conductivity, good environmental stability, and high theoretical gravimetric pseudocapacitance, has been widely applied in flexible supercapacitors. However, the conjugated PPy polymers are normally nonporous and not durable due to the decomposition after a number of charge-discharge cycles because of the swelling and shrinkage of linear macromolecular structures. Kinds of templating strategies or nanostructured supporting frameworks should be further developed to enhance the cycling stability of PPy and their specific capacitance.
In this work, we demonstrated the successful fabrication of elastic TENG and SC by using Cu@PPy sponges. The Cu@PPy sponge firstly applied to fabricate single electrode TENG. The output of the TENG was optimized by varying the PPy content in the Cu sponge or hybridization of Cu@PPy with PDMS sponge. This work can significantly promote the understanding of the triboelectricity produced by the TENG from the view of materials and provides a facile way to enhance the performance of TENG by tuning the materials itself. The Cu@PPy supercapacitor achieves high performance and overcomes the insulating problems of sponge by electrochemically interweaving sponge with a conductive polymer PPy. The deposited PPy can efficiently improve the conductivity of sponge and enhance Faradaic processes across the interface. Therefore, such hybrid-structured electrodes take the advantages of both high EDLC capacitance originated from the internal surface areas of sponge and effective pseudocapacitance generated by PPy. The assembled SC device show excellent flexibility, which has been compressed to 50% of its initial thickness and folded 180°without loss of its performance. Furthermore, for the application of the TENG and the SC, we combined the as-fabricated S-TENG with SC and manufactured a self-powered hybrid energy storage suit. The three in series SCs can be charged to 2.4 V by the S-TENG section within 3059.6 s under 3 Hz and light a LED light, which opens great prospects for integrated devices in the future. To close, because of the elasticity, flexibility, and good electric conductivity of the Cu sponge, this porous metal sponge could open new opportunities for developing wearable personal electronics and integrated devices.