Detail:

People have been searching for methods to recover energy from waste heat and vibrations for many decades. By the process of energy harvesting (also called energy scavenging), small amount of energy is derived from ambient free energy sources such as solar energy, thermal energy, kinetic energy, mechanical vibration, biochemical energy and chemical gradients. Bio-mimicking energy harvesting devices that can utilize Gibbs free energy associating with chemical gradients have attracted considerable interest. Inspired by the crosslinked network structure of animal dermis, we have designed and synthesized a polymer composite film, by combining a rigid matrix (polypyrrole) with a dynamic network (polyol-borate). In an open environment, this strong and flexible polymer film actuator absorbs water from moist substrates and then ejects bound water into low humidity air; water absorption and release is accompanied by actuator expansion and contraction that results in rapid locomotion. The contractile stress reaches 27 MPa upon water release, which is 80 times more powerful than the strongest mammalian skeletal muscle. Upon water absorption, a free actuator can raise objects 380 times heavier or transport cargo 10 times heavier than itself. We have assembled an all-polymer generator by incorporating this actuator with a PVDF-based piezoelectric element. Driven by environmental water gradients, this polymer generator outputs alternating electricity at ~0.3 Hz, with a peak voltage of ~1.0 V. The electrical energy is stored in capacitors that could power micro- and nano-electronic devices.