Waste heat efficiently converted into usable energy

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Thermoelectrochemical cells (TEC) show promise in using waste heat to generate electrical energy. However, low conversion efficiency has limited their application. Today, scientists at the Institute of Science and Technology in Daegu Gyeongbuk, Korea, have designed a new hybrid thermoelectrochemical concentration cell that outperforms similar advanced devices, opening the door to commercially energy harvesting systems. feasible that could power IoT devices and sensors. by harnessing thermal energy.

Thanks to the digital revolution underway, we are on the verge of moving to a hyper-connected world. However, Internet of Things (IoT) devices and remote sensors that promise such a reality require power. With sustainability a top priority, the energy source must be abundant, ubiquitous and renewable. Fortunately, low quality waste heat (temperatures below 100 ° C) could do the trick provided we develop efficient energy recovery technologies.

The conversion of a temperature difference into electricity is already possible thanks to thermoelectrochemical cells (TEC). These devices can harness waste heat to maintain a reduction-oxidation (redox) reaction which, in turn, produces electricity. However, today’s advanced TECs lack commercial implementations due to their low energy conversion efficiency, low power output, and expensive to manufacture. A breakthrough in energy conversion is therefore necessary for TECs to become viable for low-power unattached devices.

Against this background, a team of scientists from the Daegu Gyeongbuk Institute of Science and Technology (DGIST), Korea, devised an effective strategy to take it up a notch. Led by Professor Hochun Lee, these researchers combined the operating principle of TECs with that of concentrating galvanic cells, creating a hybrid thermoelectrochemical-concentration (TCC) cell. Although TCCs are not a new concept, the design proposed by the team overcomes some critical limitations of existing TECs.

The TCC reported in this study, which was published in the Chemical Engineering Journal, is based on redox reactions involving iodine (I-) and triiodide (I3-) ions. Unlike conventional TECs, however, these reactions occur in a non-aqueous carbonate solution that uses dimethyl carbonate (DMC) as a solvent. This particular selection of materials creates a special effect.

The researchers found that when the temperature on the hot side increased beyond 40 ° C, the DMC reacted with I− to produce a porous gel-like layer of Li2CO3 near the hot electrode which helped maintain a large difference in the concentrations of I− and I3− throughout the cell, considerably increasing its performance. “Our hybrid cell demonstrates remarkable thermal conversion efficiency (5.2%) and outperforms the best current n-type TECs,” says Professor Lee. “In addition, the simple structure and manufacturing process of our TCCs provide a practically feasible platform for thermal energy recovery. “

Further studies will be needed to refine this unprecedented approach to TCC design and hopefully achieve the goal of connecting multiple TCCs in series to achieve commercially acceptable capacities. “Companies connected to IoT will need cost-effective, self-contained power sources for their IoT devices and sensors, and we believe TECs will be the ideal candidate to meet their needs,” concludes an optimistic professor Lee.

Hopefully science will lead us to sustainable and more efficient ways to put waste heat to good use.

Reference
Kim K, Kang J, Lee H. Hybrid thermoelectrochemical and concentration cells for low quality waste heat recovery. Chem Eng J, Volume 426, December 15, 2021, 131797. doi:10.1016 / d. cej.2021.131797

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