A Triboelectric Sponge Fabricated from a Cube Sugar Template by 3D Soft Lithography for Superhydrophobicity and Elasticity

DOI: 10.1002/aelm.201500331 nanogenerator (TENG). The output voltage and current from the TES increase up to peak-to-peak values of 450 V and 0.14 mA cm −2 , respectively. This is a ten-fold power enhancement compared to those of a control group (fl at PDMS fi lm) under the same mechanical force. The electrical output performance of the TES was measured under wide ranges of mechanical stress. Various TESs were also fabricated using different grain sizes of cube sugar for various pore sizes. The output voltage and current density increase with a decrease in the pore size of the TES. Compression measurements were also conducted to evaluate the resistance to deformation by external force. These experiments showed that the elastic modulus decreases by more than 30% in a sponge typePDMS fi lm. Thus, the TES become more fl exible, and simultaneously the contact area by the micro structure increases when external mechanical force is applied. In addition, we report a very stable and high output performance of the TESs under a wide range of humidity conditions. We also show that a large number of light-emitting diodes (LEDs) can be powered by electrical output power generated by the TES under the application of mechanical strain, even in very humid conditions. Schematics for the fabrication procedure of the triboelectric sponge are shown in Figure 1 a. The fabricated TES was manufactured with 3D soft lithography with three sizes of sugar particles (see the Experimental Section for details of the fabrication steps). The sugar particles used here were commercially available in a nearby market. The cubic-shaped sugar particles used as casting templates are shown in Figure 1 c. It is seen that all sugar particles have a uniform cubic-shape. The three types of sugar particles used, large, medium, and small, have dimensions of 1500, 500, and 300 μm, respectively. As a result of casting and curing, highly porous and elastic PDMS thin fi lms were formed with the free-standing structure shown in Figure 1 a. The surface morphologies of TES fabricated with different diameters of the sugar particles are shown in Figure 1 c. This fi gure clearly shows that the PDMS sponge was very uniformly formed. Moreover, its microstructures were confi rmed by the scanning electron microscope image in Figure 1 d. To fabricate an electrical generator using the TES, thermally evaporated Au (100 nm) onto an acrylic substrate were located at one side of the TES. Then, four springs were fi xed between two electrodes for mechanical support and separation. A conceptually simplifi ed device scheme of the fabricated TES embedded generator is presented in Figure 1 b. Additionally, actual digital images of the TES are shown in Figure S1 (Supporting Information). For a fair comparison of Due to the global energy crisis and environmental problems such as global warming, energy harvesting technology has emerged as an alternative to current energy technology. Sustainable and eco-friendly energy harvesting from surrounding environment, such as solar energy, wind, tide, and mechanical vibration, has attracted a great deal of attention as researchers attempt to solve the worldwide energy crisis. [ 1 ] Thus far, diverse types of energy sources have been converted into electricity based on various physical principles, such as piezoelectric, [ 2–6 ]