Power availability remains one of the central limiting factors for the implementation of wireless sensors in many applications. For example, smart precision agriculture could increase crop yields while simultaneously reducing fresh water resources and maintaining soil health through the use of self-powered, wireless soil and moisture sensors. Wearable health sensors that are thin, flexible, and have 24/7 operation capability can provide early warnings for a wide variety of conditions such as cardiac arrhythmia and can provide real-time information for conditions such as asthma. However, such applications are often limited by the need to regularly re-charge or replace batteries. Thus, the ability to harvest enough energy directly from the environment to power such sensor systems, making them completely energy independent, could enable many applications with wide ranging societal benefits. This project will develop new technologies that can harvest power from ambient thermal energy, specifically small changes in temperature that occur daily all around us, and directly store that energy in a battery-like structure on the wireless sensor for later use. This technology could have wide-ranging applications enabling many smart environments with direct benefit to society.
The objective of this research is to explore a new approach for the direct conversion of thermal energy to stored electrochemical energy using a novel device called a "pyroelectrochemical cell" (PEC). The PEC uses a pyroelectric material (porous polyvinylidene fluoride, PVDF) as the separator of an electrochemical cell. When the PEC is heated (or cooled), the polarization of the pyroelectric separator decreases (or increases), producing a potential gradient that induces ion migration to charge the cell. The inclusion of shape memory alloy (SMA) onto the surface of the pyroelectric separator further enhances PEC charging by integrating a stress-mediated ion migration that complements the pyroelectric ion migration. To improve the energy independence of electronic devices, there is great interest in powering devices from wasted environmental energy using energy harvesting technologies, however many self-powered devices that utilize energy harvesting still require an energy storage mechanism due to intermittent energy availability. The PEC addresses this challenge by integrating thermal energy harvesting and electrochemical energy storage in a single device, eliminating the need for auxiliary device components. The goal of this work is to fully explore and mathematically model this new technology such that it can be used to support self-powered sensing operation while minimizing device size, weight, and number of components. This goal will be achieved through a combination of experimental and simulation-based tasks that seek to understand the fundamental mechanisms of ion and electron transport within the cell, explore the efficiency limit of the thermal-to-electrochemical energy conversion (both with and without inclusion of SMA), and establish design principles for integrating PEC devices in self-powered systems. The new technology and design principles will be demonstrated through the application of an optimally designed PEC to self-powered soil moisture sensors and tire pressure monitoring sensors. The proposed research will be the first exploration of integrated pyroelectric energy harvesting and electrochemical energy storage within a single device. The research will address fundamental questions related to ion and electron transport within the PEC (questions that remain unexplored in previous studies of integrated piezoelectric energy harvesting and electrochemical energy storage) and lead to new understanding of the coupled thermo-mechanical-electrochemical interactions that occur to make the PEC work.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
