UC Berkeley

Electricity is indispensable in our daily life and batteries are the widely used energy sources for portable devices in the modern world. However, harmful chemicals and wastes in batteries can lead to serious environmental and health problems without proper dispositions. As such, renewable energy sources such as solar cells have drawn lots of interests with great progresses in recent years. In this work, two forms of renewable energy harvesters based on polymers are studied based on moistures and thermal gradients in the environment. Material properties, fundamental operation mechanisms, and application demonstrations of these two renewable energy harvesters are investigated in the dissertation.

The moisture-based electric generators have long working time and high energy density output by utilizing the mechanism of the proton transportation and proton concentration oscillation. The specific polymer used in the generator has a moisture-induced oscillation surface potential from the functional groups of the polymer. Both dynamic simulation and oscillation theory have been developed to analyze this phenomenon. The self-oscillation behavior help extending the operation period of the energy harvester under the constant feeding of moistures. Experimental results show the short-circuit current density can reach 1.5 μA/cm2 and a maximum open-circuit voltage of 0.4 V with a long operation period up to 15,000 seconds with an energy density of 16.8 mJ/cm2.

The thermoelectric energy harvester has an ultra-high Seebeck coefficient and self-healing properties, which is suitable for harvesting energy from temperature gradients such as wearable devices between the human skin and the environment. The energy generator is based on the material of ionogel, which has different pore sizes and polarities to results in the very different diffusion coefficients of anions and cations. Specifically, the diffusion coefficients are characterized and simulated by using the molecular dynamic simulation under different temperatures and tested experimentally. The whole device has a measured Seebeck coefficient at 298 μV/K, which is generally higher than those of traditional thermoelectric materials. Furthermore, the prototype device is flexible, bendable and self-healable for potential applications in harvesting electrical energy for wearable devices.