Quantum computing helps discover materials that turn waste heat into electricity

The need for a transition to clean energy is obvious, urgent and unavoidable. We must limit the rise in Earth’s temperature to less than 1.5 ° C to avoid the worst effects of climate change, a particularly daunting challenge in the face of ever-increasing global demand for energy.

Part of the answer lies in the more efficient use of energy. Over 72% of all energy produced in the world is lost as heat. For example, a car’s engine only uses about 30% of the gasoline it burns to power the car. The rest is dissipated as heat.

Recovering even a tiny fraction of this wasted energy would have a huge impact on climate change. Thermoelectric materials, which convert waste heat into useful electricity, can help.

Until recently, the identification of these materials had been slow. My colleagues and I used quantum calculations – a computer modeling approach to predict the properties of materials – to speed up this process and identify more than 500 thermoelectric materials that could convert excess heat into electricity and help improve efficiency. energetic.

Make great strides towards broad applications

The transformation of heat into electrical energy by thermoelectric materials is based on the “Seebeck effect”. In 1826 the German physicist Thomas Johann Seebeck observed that exposing the ends of dissimilar metal attachments to different temperatures generated a magnetic field, which was later recognized to be caused by an electric current.

Shortly after its discovery, metal thermoelectric generators were made to convert heat from gas burners into electric current. But, as it turned out, metals show only a weak Seebeck effect – they are not very efficient at converting heat into electricity.

The kerosene radio was designed for rural areas and was powered by the kerosene lamp suspended above. The flame created a temperature difference between the metals to generate the electric current. Image via ‘Popular Science’, Issue 6, 1956

In 1929, the Russian scientist Abraham Ioffe revolutionized the field of thermoelectricity. He observed that semiconductors – materials whose ability to conduct electricity lies between that of metals (like copper) and insulators (like glass) – exhibit a significantly higher Seebeck effect than metals, multiplying by 40 the thermoelectric efficiency, 0.1 percent to four percent.

This discovery led to the development of the first widely used thermoelectric generator, the russian lamp – a kerosene lamp that heated a thermoelectric material to power a radio.

Are we there already?

Today, thermoelectric applications range from power generation in space probes at cooling devices in portable refrigerators. For example, space exploration is powered by radioisotope thermoelectric generators, converting the heat of naturally decomposing plutonium into electricity. In the movie The Martian, for example, a box of plutonium saved the life of the character played by Matt Damon, keeping him warm on Mars.

In the 2015 film, The Martian, astronaut Mark Watney (Matt Damon) digs up a buried thermoelectric generator to use the power source as heating.

Despite this great diversity of applications, the large-scale commercialization of thermoelectric materials is still limited by their low efficiency.

What is holding them back? Two key factors must be considered: the conductive properties of materials, and their ability to maintain a temperature difference, which allows electricity to be generated.

The best thermoelectric material would have the electronic properties of semiconductors and the poor thermal conduction of glass. But this unique combination of properties is not found in natural materials. We have to design them.

Looking for a needle in a haystack

Over the past decade, new strategies for designing thermoelectric materials have emerged due to a better understanding of their underlying physics. In one recent study in Natural materials, researchers from Seoul National University, Aachen University and Northwestern University said they designed a material called tin selenide with the highest thermoelectric performance to date, almost double those of 20 years ago. But it took them almost a decade to optimize it.

To speed up the discovery process, my colleagues and I used quantum calculations to search for new high efficiency thermoelectric candidates. We searched a database of thousands of materials to find those that would have high electronic qualities and low levels of thermal conduction, based on their chemical and physical properties. This information helped us find the best materials to synthesize and test, and calculate their thermoelectric efficiency.

We are almost at the point where thermoelectric materials can be widely applied, but first we need to develop materials that are much more efficient. With so many possibilities and variables, finding a way forward is like looking for a small needle in a huge haystack.

Just as a metal detector can focus on a needle in a haystack, quantum calculations can accelerate the discovery of efficient thermoelectric materials. Such calculations can accurately predict electronic and thermal conduction (including the Seebeck effect) for thousands of materials and reveal the previously hidden and very complex interactions between these properties, which can influence the efficiency of a material.

Large-scale applications will require inexpensive, non-toxic, and abundant thermoelectric materials. Lead and tellurium are present in thermoelectric materials today, but their cost and negative environmental impact make them good replacement targets.

Quantum calculations can be applied in a way that searches for specific sets of materials using parameters such as scarcity, cost, and efficiency. While these calculations can reveal optimal thermoelectric materials, synthesizing materials with the desired properties remains a challenge.

A multi-institutional effort involving government laboratories and universities in the United States, Canada and Europe revealed more than 500 previously unexplored materials with high predicted thermoelectric efficiency. My colleagues and I are currently investigating the thermoelectric performance of these materials in experiments and have already discovered new sources of high thermoelectric efficiency.

These early results strongly suggest that further quantum calculations can identify the most efficient combinations of materials to generate clean energy from wasted heat and avert the catastrophe that threatens our planet.The conversation

This article from Jan-Hendrik Pohls, McCall MacBain Postdoctoral Fellow, Department of Chemistry and Chemical Biology, McMaster University, is reissued from The conversation under a Creative Commons license. Read it original article.

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