EXCLUSIVE INTERVIEW WITH ETH/EMPA "Finding sustainable electrical conductors to substitute conventional ones is of vital importance for green electronics"

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The use of sustainable electronic components is becoming increasingly relevant due to procurement difficulties. Thanks to a new process, wood can be made electrically conductive very efficiently, which leads to fast processing times. In this exclusive interview with Power & Beyond, Christopher Dreimol, doctorate at ETH Zürich, explains how it is possible to make wood electrically conductive and in which areas the new process can be applied.

The fact that industry needs to rethink their production methods towards increased sustainability has been known for years. With increasing awareness of climate change, pressure from customers and politicians on companies has risen, and with it the need to invest in appropriate research. One of the main areas of research within power electronics is new sustainable materials.
For example, we recently reported on a paper battery with water switch and wood-based batteries that Northvolt and StoraEnso are developing in cooperation. And last but not least, we reported that a research team at Empa and at ETH's Institute for Building Materials has developed a practical and versatile method for making wooden surfaces electrically conductive. An exciting approach that we would like to explore in this exclusive interview with Christopher Dreimol, doctorate at ETH Zurich.

About Christopher Dreimol

After completing an apprenticeship in the field of mechanical engineering at Kathrein SE in Rosenheim, Christopher Dreimol studied Biomimetics (B.Sc.) in the HS Bremen. He continued with a Master in Production Engineering with a focus of material science at the University of Bremen that he finished with a master thesis in ETH Zürich working on bio-inspired materials. Today as a Ph.D. student, Christopher Dreimol works on sustainable wood-based electronics for smart buildings together with Prof. Dr. Ingo Burgert and Dr. Guido Panzarasa in the Wood Material Science Group at ETH Zürich and EMPA.

Mr. Dreimol, recently we have reported that Stora Enso and Northvolt are working on producing wood-based batteries and now you have also found a way to use wood for the production of electronic components. Can you briefly summarize what exactly you have accomplished?

We made wood electrical conductive via a novel process called iron-catalyzed laser-induced graphitization (IC-LIG). The process combines the catalytic effect of an iron-containing ink together with a CO₂-laser process. By catalysing the graphitization process, it is now possible to engrave patterns in thin wood veneers even from different wood species, resulting in very good conductivity and fast processing times.

Unlike the battery project of Stora Enso and Northwolt, we are using directly wood (veneers) instead of chemically extracted lignin. In addition, our focus for this project was not on generating energy using wood, but rather to make its surface electrically conductive, a challenging task given the natural complexity and inhomogeneity of wood. By producing sensors and electroluminescent devices directly on wood veneers, we demonstrated the enabling power of IC-LIG for making homogeneous and uniform graphitized surfaces.

What were your motives for carrying out this research project?

First, it is necessary to understand that working with wood can be a very challenging task, considering its inhomogeneous surface structure and density variations. Making wood and wood-derived materials electrically conductive was possible before, but former laser-based processes often required long processing times and the use of fire retardants and inert atmospheres. Furthermore, issues like high ablation of the wood surface, thermal damages and need for multiple lasing steps to achieve reasonable electrical properties posed limitations to applicability and scalability of these processes.

With IC-LIG, we tried to meet these challenges and address various fields of applications for wood-based electronics by using only sustainable chemicals in combination with wood as a carbon precursor and substrate.

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You stated that you wanted to refine and further develop the process for large-scale use. But isn't it questionable, in view of deforestation, to use even more wood for industry purposes?

Deforestation is certainly a critical issue of the last centuries. The increase in the demand of forest-based products, with further developments in the building sector and the rise of products like biofuels and wood-derived chemicals, makes it even more relevant. However, wood is a renewable resource with great potential to be used as CO₂-storing material and for substituting non-renewable materials. Therefore, to enable a sustainable forest-based circular bio-economy it is necessary to base timber provision on sustainable forest management of healthy forests with a high biodiversity. This also means avoiding to focus on single wood species from monocultures, but rather focus on diversity, especially in times of climate change.
With our IC-LIG we demonstrated that we can process conductive structures using a large variety of wood species and turn wood into a product of high value.

What role do you think wood will play in the production of electronic components in the future?

As mentioned before, the use of wood especially in the building sector is increasing. The reasons are manifold: awareness of people to use more sustainable building materials, or the unique aesthetic of the wood material. Wood can be used for structural components even in high-rise multi-story buildings. Therefore, sensors may be directly integrated as “wooden electronics” in future smart homes (touch sensors) as well as for health monitoring of structural timber components (e.g. strain sensors).

Sustainable wood-based circuit boards can be interesting alternatives to current printed circuit boards (PCB). State-of-art PCBs are highly problematic to recycle since they contain a multitude of different metals that are very difficult to separate. Moreover, current processes to “urban mine” and recycle the metals are time consuming, and due to thermodynamic incompatibilities, there are always trade-offs and inevitable losses of specific metal fractions. Finding suitable alternative materials to rare metals is thus of vital importance. In this regard, carbon-based electronics is of special interest. However, some challenges have yet to be met using wood as a substrate, since the required electrical conductivity and resolution to engrave conductive paths for PCBs has not been achieved yet. We aim at developing further our processes and optimize wood surfaces as well as sustainable plastics as substrates and precursors for future sustainable electronic materials.

Do you have any other sustainable materials in mind besides wood that could revolutionize power electronics in a few years' time?

We are working currently on different substrates to establish IC-LIG for a variety of applications. Since we envision a trend towards flexible, transparent and transient electronics, especially for consumer devices, it is feasible to explore materials that meet such requirements for example flexible, but transparent, wood composites.

Nowadays, material development is still mainly driven by economic requirements. However, other aspects such as resource depletion and availability may become more prominent in the next years and decades. Future materials need to be as sustainable as possible. This requires considering properties beyond the targeted performance (e.g. the electrical conductivity), including the entire live cycle and ensuring their reusability and/or recyclability.

Thank you for the interview, Mr. Dreimol!

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