3 Questions: Howard Katz on the Power of Plastics

Winter 2023

Plastics are known forHoward Katz black and white photo of him smiling in front of trees with plaid shirt. being robust and flexible, but most aren’t particularly good conductors of electricity; in fact, they are often used to insulate power cables. A team of Johns Hopkins engineers led by Howard Katz, professor and chair of the Department of Materials Science and Engineering, used a new polymer (plastic) material combination to create a conducting material blend that has the superior ability to remain stable at a variety of temperatures and is more capable of generating electrical power from waste heat than are previous plastic blends. Their results recently appeared in Advanced Materials.

1. What were you trying to do?

We wanted to create a material that is flexible and printable and that can be used to conduct electrons. Flexibility allows use on nonrigid surfaces like skin and paper. Printability allows deposition of the materials without using expensive vacuum processes or high temperatures. The most successful commercial electrically conducting polymer-based material primarily conducts positive charges. We created a material with a highly analogous structure that primarily conducts electrons, which are negatively charged.

2. How did you give plastic the ability to conduct electricity?

We used a polymer of a positive salt ion to alter the composition and characteristics of another polymer to enhance its ability to conduct electrons—a process called “n-doping.” N-doping has been used in creating organic transistors, solar cells, photocatalysts, and light-emitting diodes (LEDs). Using such salts as dopants is relatively new. We were simply the first to think of combining the salt and polymer dopant concept for electrons, and it worked. We were inspired by polymers that primarily conduct positive charges, called “holes.” The most commercially successful of these materials uses a second polymer to form the holes, and my team thought this approach could work for us too.

3. How might this new material be used?

We think that it could be particularly useful in thermoelectrics, in which heat is used to generate electrical power. Thermoelectric devices are made with subsections that
each conduct positive and negative charges exclusively. The material could be used as a conductive layer on the side of solar cells or LEDs where electron conduction is needed.
There are many design changes that we could make in the polymers to improve performance further; this work is in progress.

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