Direct Thermal Charging Cell for Harvesting Body Heat 

Project: Research

View graph of relations

Description

Efficient low-grade heat recovery is of importance to abating greenhouse-gas emissions as over 70% of primary energy input is wasted as heat. Low-grade heat is abundantly available in the environment, in solar thermal and geothermal energy, and even in human body heat, which could be valuable for recycling and converting into electricity. However, the efficient conversion of low-grade heat into electricity is still a great challenge. Extensive research has been conducted in solid-state thermoelectric (TE) materials, yet current TEs working within 100oC suffer low energy conversion efficiency (ηE). Alternative approaches based on liquid-based thermoelectrochemical cells (TECs) have attracted attention as their ionic Seebeck coefficient (α) is one order of magnitude higher than that of TE semiconductors. Current TEC technologies, such as thermogalvanic cells (TGCs), thermally regenerative electrochemical cycles (TRECs), thermally regenerative ammonia batteries (TRABs) and redox flow batteries (RFBs), are capable of converting low-grade heat into electricity, but theirηEis either too low or system is too complex for economical deployment. Recently, we reported a new electrochemical system named direct thermal charging cell (DTCC) using asymmetric electrodes of a graphene oxide (GO) anode and a polyaniline (PANI) cathode sandwiched with an aqueous Fe2+/Fe3+-based redox electrolyte. DTCC can be thermally charged in open-circuit condition via the thermo-pseudocapacitive effect of GO, and current is then produced with PANI and Fe2+/Fe3+switching between their redox forms when an external circuit is connected, achieving a markedly high α of 5.0 mV/K and anηEof 3.5% in a low-grade heat regime (equivalent to 20% of Carnot efficiency, ηC). The operating temperature is 40 − 90°C. The system can be self-regenerated when cooled down to room temperature, allowing DTCCs to be cyclable. DTCCs are therefore a promising technology, with low cost, simple system, and the ability to be stackable and flexible, setting DTCCs ahead of the existing TECs and TEs for low-grade heat recovery. This project will further develop DTCC technology toward operation at human skin temperature (~32°C), such that DTCCs will be applicable to body-heat harvesting for self-powered sensing electronics. We will search for a new anode material with large negative α and small anodic onset potential, and engineer redox couples with large entropy change to better improve device performance, cycling stability, and operating temperature window. Synchrotron radiation and in situ Raman spectroscopy will be used to advance our fundamental understanding of the thermo-pseudocapacitive reaction at the GO-electrolyte interface regarding thermal voltage generation. 

Detail(s)

Project number9043285
Grant typeGRF
StatusFinished
Effective start/end date1/09/2012/08/24