A triboelectric nanogenerator (TENG) is a novel technology with applications in many areas, including energy harvesting, self-powered sensing, medication, and electronics. The materials used as triboelectric layers are diverse and include polymers, metals, and inorganic materials. The most commonly used materials are dielectric polymers such as PTFE, FEP, PDMS, and Kapton. Green materials, such as cellulose-based materials, have recently gained increasing interest, and the performance of TENGs using cellulose materials has improved. The material choices are of great importance for TENGs since the triboelectric effects of the materials are fundamental for TENGs. To design a TENG for a particular application, several parameters need to be considered, such as power density, stability, flexibility, and sustainability. This critical review will summarize and evaluate the material choices for TENGs in different applications.

HIGHLIGHTS • The development of bismuth ferrite as a multiferroic nanomaterial is summarized. • The morphology, structures, and properties of bismuth ferrite and its potentialapplications in multiferroic devices with novel functions are presented anddiscussed. • Some perspectives and issues needed to be solved are described.

Many solution processing methods of exfoliation of layered materials have been studied during the last few years; most of them are based on organic solvents or rely on surfactants and other funtionalization agents. Pure water should be an ideal solvent, however, it is generally believed, based on solubility theories that stable dispersions of water could not be achieved and systematic studies are lacking. Here we describe the use of water as a solvent and the stabilization process involved therein. We introduce an exfoliation method of molybdenum disulfide (MoS2) in pure water at high concentration (i.e., 0.14 ± 0.01 g L−1). This was achieved by thinning the bulk MoS2 by mechanical exfoliation between sand papers and dispersing it by liquid exfoliation through probe sonication in water. We observed thin MoS2 nanosheets in water characterized by TEM, AFM and SEM images. The dimensions of the nanosheets were around 200 nm, the same range obtained in organic solvents. Electrophoretic mobility measurements indicated that electrical charges may be responsible for the stabilization of the dispersions. A probability decay equation was proposed to compare the stability of these dispersions with the ones reported in the literature. Water can be used as a solvent to disperse nanosheets and although the stability of the dispersions may not be as high as in organic solvents, the present method could be employed for a number of applications where the dispersions can be produced on site and organic solvents are not desirable.

Triboelectric nanogenerators (TENGs) have attracted increasing attention because of their excellent energy conversion efficiency, the diverse choice of materials, and their broad applications in energy harvesting devices and self‐powered sensors. New materials have been explored, including green materials, but their performances have not yet reached the level of that for fluoropolymers. Here, a high‐performance, fully green TENG (FG‐TENG) using cellulose‐based tribolayers is reported. It is shown that the FG‐TENG has an output power density of above 300 W m−2, which is a new record for green‐material‐based TENGs. The high performance of the FG‐TENG is due to the high positive charge density of the regenerated cellulose. The FG‐TENG is stable after more than 30 000 cycles of operations in humidity of 30%–84%. This work demonstrates that high‐performance TENGs can be made using natural green materials for a broad range of applications.

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