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SUMMARYPyroelectric conversion utilizes low-grade waste heat as a heat source, and thus produces clean energy. Low-grade heat is abundant in the various industries and it is practically free. It can be converted to high-voltage electricity by pyroelectric conversion. Our pyroelectric converter uses copolymer of poly-vinylidene fluoride with trifluoroethylene [60/40% P(VDF-TrFE)]. Previously, we encountered a substantial power loss due to internal leakage at high temperature and voltage. In order to increase the power output, we examined the effect of polymer purification using solvent extraction. We compared the electrical properties of purified copolymer with those of 'as-received' copolymer. Although we removed only 0.4 wt% of the copolymer by solvent extraction, the electrical resistivity of purified copolymer was 35% higher than that of the 'as-received' copolymer. We also observed that thin films produced using purified copolymer were able to withstand 50% higher electric field before they were ruined by the electrical short circuit. Subsequently, we conducted pyroelectric conversion using 25 m m thick 60-40% P(VF 2 -TrFE) copolymer films. Copolymer purification resulted in a three-fold increase in net power output. Net power output per unit volume of the 'as-received' copolymer was 95 J L À1 but it increased to 279 J L À1 for purified copolymer.

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