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In operandotechniques have emerged to elucidate the fundamental mechanism of triboelectrification via relevant physical quantity measurement during the physical contact of two materials. Here, a correlation between frictional heat and triboelectric charge is reported in a metal-polymer triboelectric nanogenerator through the in operandotemperature measurement. Fluorine-doped tin oxide (FTO) metal is slid back-and-forth under different contact pressures across polydimethylsiloxane (PDMS) polymers having different degrees of crosslinking, i.e., mixing ratio. Both the triboelectric charge and temperature variation increase and become saturated with different time-constants. Notably, the saturated triboelectric charge increases, while the saturated temperature decreases, with increasing mixing ratio. In contrast, both saturated triboelectric charge and temperature increase with increasing contact pressure. X-ray photoemission spectroscopy reveals that chemical bonds are modified inhomogeneously at the surface, and that charged materials are transferred from PDMS to FTO in accordance with the mixing ratio- and sliding time-dependent triboelectric charges. Frictional heat plays a distributive role in bond rupture and temperature variation, depending on the activation energy and frictional coefficient of PDMS. In operandotemperature variation measurement provides important information on the specific bonds for triboelectrification and detailed charge-transfer process during physical contact.

Recently, we reported surface fluorination of sulfur-based polymers to introduce a new class of extremely negative triboelectric material. However, the direct surface fluorination requires the use of toxic fluorine gas. In this study, we report the toxic gas-free synthesis of extremely negative triboelectric sulfur-rich polymers via the phase separation of a fluorine-rich polymer, poly(2,3,4,5,6-pentafluorostyrene) (PPFS), from sulfur copolymers. PPFS was physically mixed in situ during the inverse vulcanization of elemental sulfur, a by-product of petroleum refining to prepare the polymer blends. Hot pressing of the blends into films induced the phase separation of the hydrophobic PPFS; subsequently, PPFS migrates to the hydrophobic air interface to minimize the interfacial energy. A triboelectric nanogenerator (TENG) based on the phase separated blend films presented long-term stable voltage and current outputs that are 8-fold and 9-fold higher, respectively, than those of a TENG based on polytetrafluoroethylene (PTFE), a well-known extremely negative triboelectric polymer. We also demonstrate the ability of a TENG based on a 81.1 cm2-sized blend film to power 400 series-connected blue LEDs of 3.3V; a triboelectric open-circuit voltage output of 1362.4V is obtained under a minimal force of 30N. The demonstrated phase-separation strategy for fluorine-rich polymers will thus provide insights for achieving low-cost, environment-friendly, and high-performance triboelectric energy harvesting.