If you’ve ever looked at yourself with a thermal imaging camera, you know that your body produces a lot of heat. It is actually a waste product of our metabolism. Each square meter of the human body produces heat equivalent to approximately 19 matches per hour.

Unfortunately, a significant part of this heat escapes into the atmosphere. Wouldn’t it be great if we could use this to generate energy? My research has shown that this is indeed possible. My colleagues and I are looking for ways to capture and store body heat for energy production using environmentally friendly materials.

The goal is to create a device that can both generate and store energy, serving as an integrated power source for wearable devices. This could allow devices such as smartwatches, fitness trackers, or GPS trackers to operate for much longer, or even indefinitely, using our body heat.

It’s not just our body that produces waste heat. In our technologically advanced world, a significant amount of waste heat is generated every day, from the engines of our vehicles to the machines that produce goods.

Typically this heat is also released into the atmosphere, meaning a significant loss of opportunity for energy recovery. The new “waste heat recovery” concept aims to solve this inefficiency. By utilizing this energy that would otherwise be wasted, the industry can increase its operational efficiency and contribute to a more sustainable environment.

The thermoelectric effect is a phenomenon that can help convert heat into electricity. The way it works is that as electrons flow from the hot side to the cold side, the temperature difference creates an electrical potential and produces useful electrical energy.

But traditional thermoelectric materials are usually made of cadmium, lead or mercury. They are associated with environmental and health risks that limit their practical use.

The strength of wood

But we discovered that you can also create thermoelectric materials from wood, which offers a safer and more durable alternative.

Wood has been an integral part of human civilizations for centuries, serving as building materials and a source of fuel. We uncover the potential of wood materials to convert waste heat often lost in industrial processes into valuable electricity. This approach not only improves energy efficiency, but also redefines the way we view everyday materials as important components of sustainable energy solutions.

Our team at the University of Limerick, in collaboration with the University of Valencia, has developed an environmentally friendly method of converting waste heat into electricity using Irish wood products, specifically lignin, a by-product of the paper industry.

Our research shows that lignin-based membranes immersed in brine solution can efficiently convert low-temperature waste heat (below 200 °C) into electricity. The temperature difference between the lignin membrane causes the ions (charged atoms) in the salt solution to move.

Positive ions move to the cold side and negative ions move to the hot side. This separation of charges creates an electrical potential difference across the membrane that can be used as electrical energy.

Since approximately 66 percent of industrial waste heat falls within this temperature range, this innovation opens up significant opportunities for environmentally friendly energy solutions. This new technology can make a big difference in many areas. Industries such as manufacturing that generate large amounts of waste heat can benefit greatly from converting this waste heat into electricity. This will help them save energy and reduce their impact on the environment.

This technology can find applications in a variety of situations, from providing power in remote areas to powering sensors and devices in everyday applications. Its environmental friendliness also makes it a promising solution for sustainable energy production in buildings and infrastructures.

storage problem

Generating energy from waste heat is only the first step; Its effective storage is no less important. Supercapacitors are energy storage devices that quickly charge and discharge electricity. This makes them indispensable for applications requiring fast power.

However, their dependence on fossil fuel-derived carbon materials raises sustainability concerns and underscores the need for renewable alternatives in their production. Our research group discovered that lignin-based porous carbon can serve as electrodes in supercapacitors to store energy obtained from harvesting waste heat using lignin membrane.

This process enables the lignin membrane to capture waste heat and convert it into electrical energy, while the porous structure of carbon facilitates the rapid movement and accumulation of ions. Providing an environmentally friendly alternative that avoids the use of harmful chemicals and fossil fuels, this approach offers a sustainable solution for storing energy from waste heat.

This innovation in energy storage technology could power everything from consumer electronics to portable devices and electric cars.