Zinc Oxide Used to Convert ‘Waste’ Heat to Electricity

By James Wellstead – Exclusive to Zinc Investing News

Recent techniques developed in nanoengineering have made zinc oxide (ZnO) an ideal material for the growing market of ‘energy harvesting’ technologies. These devices convert ambient or ‘waste’ energy—derived from sources as diverse as human power, body fluids, heat differences, vibration, or visible light—into electricity and are a central technology in the future of ‘smart’ electronics.

Researchers at Rensselaer Polytechnic Institute in Troy, New York announced that they have successfully developed a new method of converting waste heat into electricity by altering zinc oxide’s material properties. The research team led by Ganpati Ramanath, in collaboration with researchers at the University of Wollongong in Australia, increased ZnO’s electrical conductivity (its ability to transfer an electric current) while reducing its ability to transfer heat by baking the metal with aluminum in a common household microwave oven.

Unlike many nanomaterials that are fabricated directly onto a surface, the new microwave method produces marble-sized pellets that can be applied to different surfaces making them adaptable for a wide range of energy harvesting applications.

Ramanath said that his team is “the first to demonstrate such favourable thermoelectric properties in bulk-sized high-temperature materials, and we feel that our discovery will pave the way to new power harvesting devices from waste heat.”

Current commonplace energy harvesting applications have included the application of photovoltaic cells on calculators and roadside electronic signs or bicycle dynamos to power lights or radios. However a number of advances in nanotechnology have expanded the variety and complexity of applications and can now be found powering pacemakers from contractions of the heart to controlling lighting and heating of buildings through temperature sensitive sensors.

ZnO and energy harvesting

The development of these new aluminum-doped zinc oxide pellets offer new opportunities to expand heat to electricity conversion in a number of commonplace electronics such as laptops, cell phones and televisions. These advancements will allow the respective technologies to reduce the devices’ energy consumption and enable them to become increasingly self-sufficient – often for years.

But because of the malleability of the pellet forms, opportunities for larger applications also exist in cars, aircraft, and even power plants. Ramanath says that “our process is amenable to scaling for large-scale production”, which “would lead to greater efficiency in nearly everything we do and, ultimately, reduce our dependence on fossil fuels.”

While ZnO’s suitability for energy harvesting applications is limited by the specific type of available ambient energy, other thermo-electric materials (those which conduct electricity through temperature difference) have already evolved into a number of prototypes, such as Volkswagen’s 2009 concept car which in 2008 was able to increase fuel efficiency by 5 percent.

Expanding ZnO’s Uses

This is not the first use of ZnO as an energy harvesting material. Researchers at Georgia Institute of Technology have successfully developed zinc oxide nano-wires which can be inserted onto the human heart to power other nano-sized devices that detect blood pressure, glucose levels or hypoglycaemia. Expansion of ZnO into larger-scale energy harvesting applications, however, could lead to wider changes in the ZnO market which currently accounts for about 9 percent of the total zinc consumption and is focused primarily in the production of tires, ceramic tiles, medicines and household paints.

ZnO is a prime candidate for a variety of energy harvesting applications because of its high electrical conductivity and melting point, as well as being non-toxic and inexpensive. High material prices have been a persistent challenge for the energy harvesting industry in recent years, limiting the use of several materials.

Zinc prices have been sliding over the past three months, as three-month forward prices for zinc have fallen from around US $2,500 per tonne at the end of July to just below $1,900 in late October. Further, the persistently high surplus levels of zinc in the world markets make the material a relatively safe and accessible source for expanded applications.

While commercial application of the ZnO pellets are still a ways off, these recent developments offer a promising opportunity for the pellets application in a number of markets. While not the only oxide capable of converting heat to electricity, ZnO is positioned to become a competitive and low-cost material in a world which will see nanomaterials play an increasingly important role.