This work presents for the first time the systematic characterization and excellent supercapacitor performance of heteroatom-doped porous carbon materials (HPC) synthesized by direct pyrolysis of watermelon peel and urea via molten salt template route in air with non-toxic activating agent. The molten salt not only protects the derived carbon from burning during hightemperature pyrolysis, but can also be etched to generate abundant hierarchical pores in the final products. The obtained HPC exhibits a high specific surface area of 1660 m 2 g À 1 and shows high specific capacitances of up to 278 F g À 1 in 1 M H 2 SO 4 electrolyte. The symmetrical device also demonstrates a remarkable specific capacitance of up to 226 F g À 1 and ultrahigh initial capacitance retention of 98 % after 10,000 cycles of charge/discharge at the current density of 10 A g À 1. The porous carbon produced via this green chemical activation route demonstrates great potential as electrode materials in supercapacitor.

The development and utilization of switchable adhesives are considered to be an essential target to solve the problems of their separation and recycling in some specific service environments, such as the preparation or repair process of electronic devices. Intelligent materials with controllable phase transition are utilized to fabricate switchable adhesives because of the significantly diverse adhesion strengths in different phase states. Photoresponsive azobenzene and its derivatives usually possess different melting temperatures (T m) or/and glass transition temperatures (T g) of the cis–trans isomers, which are beneficial to making the photoinduced solid–liquid phase transition for switchable adhesive application possible. Here, a novel three-component azo-copolymer (PNIM-Azo) with fast and reversible photoinduced solid–liquid phase transition has been designed and synthesized. PNIM-Azo possesses reversible bonding/debonding processes, resulting from the different adhesion strengths between trans-configuration PNIM-Azo in the solid state and cis-configuration in the liquid state. Moreover, by incorporating commercialized 2-methoxyethyl acrylate and N-isopropylacrylamide with O and N heteroatoms into the copolymer, the trans-configuration PNIM-Azo possesses the highest adhesion strength (∼11 MPa between two glass substrates) among all of the reported azobenzene-based switchable adhesives, which could be attributed to the increase in the entanglement effect because of the H-bond in the polymer chains formed by introducing heteroatoms. Our synthesized PNIM-Azo copolymer provides an alternative for designing and developing switchable adhesives with high adhesion strength for some electronic production processes.

Flexible strain sensors have recently attracted great attention due to their promising applications in human motion detection, healthcare monitoring, human–machine interfaces, and so forth. However, traditional uniaxial strain sensors can only detect strain in a single direction. Herein, an anisotropic flexible strain sensor is fabricated based on conductive and highly aligned cellulose composite nanofibers, via facile electrospinning cellulose acetate, deacetylation, and in situ polymerization of pyrrole, to detect complex multidimensional strains. Benefiting from the unique well-ordered structure of conductive composite nanofibers, the obtained strain sensor shows extraordinary anisotropic sensing performance with a sensitivity of 0.73 and 0.01 for the tensile applied perpendicular and parallel to the nanofiber alignment, respectively. The sensor also exhibits outstanding durability (2000 cycles) due to the strong hydrogen bonding between cellulose nanofibers and polypyrrole. Moreover, the flexible strain sensors exhibit promising potentials for application in motion detection, as demonstrated by the detection of various joint movements in the human body.

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Recently, sustainable triboelectric nanogenerators (TENGs) based on biodegradable biomaterials have attracted tremendous attention to efficiently harvest mechanical energy in a cost-effective and environment-friendly strategy. Lignin, as the second most abundant...