Effect of testing modes and voltmeter resistance on mechanoelectrical conversion of electrospun polyvinylidene fluoride nanofiber membranes

This study examines several important aspects of electrospun polyvinylidene difluoride nanofibers for mechanical-to-electrical energy conversions, such as the effects of voltmeter resistance and testing modes on the electrical characterizations, the source of electrical generation, the force response, and roles of each electrode. We used a voltmeter with different inner resistances to test the output voltage, power, and device internal resistance under two testing modes, (1) constant-contact and (2) contact-separation. The results showed that the voltmeter resistance indeed impacted the measurements profoundly, regardless of the testing modes. We then examined the contribution of various energy conversion principles to the voltage outputs. It was found that the energy conversion involved approximately 49.1% piezoelectric and 50.9% electret effects in the constant-contact mode. In contrast, the energy conversion in the contact-separation mode involved triboelectric, piezoelectric, and electret effects, taking approximately 28.6%, 39.7%, and 31.7%, respectively. The eliminated electret effect could recover in the contact-separation mode. The nanofiber membrane side that received the mechanical force predominated voltage outputs. The electrical outputs generated by polyvinylidene difluoride nanofibers are of an alternating current and can be stored in capacitors only if rectification. We hope these understandings will assist in evaluating mechanoelectrical nanofibers and developing high-performance energy harvesters.