New Sensitized Thermal Cells Generate Electricity

A team of scientists at the Tokyo Institute of Technology, led by Dr. Sachiko Matsushita, has made great progress in the understanding and development of the new “sensitized thermal cells” (STCs), a kind of battery that can generate electric power at 100° C or less. The team has developed a very stable battery cell that can directly convert heat into electricity, thus finally providing a way for exploiting geothermal energy in a sustainable way.

In a world where energy consumption is on the rise, progress relies on the development of new energy-generation technologies. Although currently used renewable energy sources such as wind and solar energy have their merits, there is a gigantic, permanent, and untapped energy source quite literally beneath our feet: geothermal energy. But generating electricity from geothermal energy requires devices that can somehow make use of the heat within the Earth’s crust.

Several methods for converting heat into electric power exist, however, their large-scale application is not feasible. For example, hot-and-cold redox batteries and devices based on the Seebeck effect are not practical to simply bury them hundreds or thousands of feet down inside a heat source and exploit them.

The team’s research paper describing the work has been published in the Journal of Materials Chemistry A.

Dr. Matsushita’s team has previously reported the use of STCs as a new method for converting heat directly into electric power using dye-sensitized solar cells. They also replaced the dye with a semiconductor to allow the system to operate using heat instead of light.

The STC, a battery consists of three layers sandwiched between electrodes: an electron transport layer (ETM), a semiconductor layer (germanium), and a solid electrolyte layer (copper ions). In short, electrons go from a low-energy state to a high-energy state in the semiconductor by becoming thermally excited and then get transferred naturally to the ETM.

Afterwards, they leave through the electrode, go through an external circuit, pass through the counter electrode, and then reach the electrolyte. Oxidation and reduction reactions involving copper ions take place at both interfaces of the electrolyte, resulting in low-energy electrons being transferred to the semiconductor layer so that the process can begin anew, thus completing an electric circuit.

However, it was not clear at that time whether such a battery could be used as a perpetual engine or if the current would stop at some point. After testing, the team observed that electricity indeed stopped flowing after a certain time and proposed a mechanism explaining this phenomenon.

Basically, current stops because the redox reactions at the electrolyte layer stop owing to the relocation of the different types of copper ions. Most importantly, and also surprisingly, they found out that the battery can revert this situation itself in the presence of heat by simply opening the external circuit for some time; in other words, by using a simple switch. “With such a design, heat, usually regarded as low-quality energy, would become a great renewable energy source,” stated Matsushita.

The team is very excited about their discovery because of its applicability, eco-friendliness, and potential for helping solve the global energy crisis. “There is no fear of radiation, no fear of expensive oil, no instability of power generation like when relying on the sun or the wind,” remarked Matsushita.

Further refinements to this type of battery will be the aim of future research, with the hope of one day solving humanity’s energy needs without harming our planet.

Its always a moral boost when a new technology comes into view. While still in its infancy the bold idea of a sensitized thermal cell that functions is full of hope as Matsushita noted. Where this technology might lead to is anyone’s guess as there is a huge array of heat harvesting opportunities right now.

The real stimulant though is the suggestion of operation at 100° C or even less. At or below the mere boiling point water for heat harvesting is definitely a heads up technology.