Thermoelectric materials allow to directly convert waste heat into electricity without requiring any moving parts. Abundant and non-toxic organic materials present an opportunity towards cheaper renewable energy generation because they can be solution-processed at low temperatures.
One example of a sustainable thermoelectric material is described in the work published in ENERGY & ENVIRONMENTAL SCIENCE, where we use bacteria to grow thermoelectric paper. In solution, some bacteria produce pure cellulose, similar to what happens during the preparation of the fermented drink Kombucha or the dessert “nata de coco”. Adding dispersed carbon nanotubes to their usual glucose-rich nutrient mixture results in a finely intermixed cellulose-nanotube nanocomposite film.
Compared to buckypaper (films made of solely carbon nanotubes), these composites contain 90 % fewer carbon nanotubes without degraded thermoelectric performance. While they do have lower electrical conductivity due to the insulating cellulose, they more than makeup for it by their lower thermal conductivity. As a bonus, these composites exhibit novel and interesting properties. For example, they can be “digested” using enzymes, leaving behind a carbon nanotube aerogel that can be recycled. Furthermore, cellulose can be molded to conformally attach to irregular or rough surfaces, ensuring optimal thermal contact. Importantly, compared to other thermoelectric polymers, both carbon nanotubes and cellulose have relatively high thermal stability, which is of particular importance for thermoelectric applications. This work has been highlighted in media devoted to both academics (e.g. Nature Nanotechology, Royal Society of Chemistry, CSIC, etc.) and all-public (La Vanguardia, Muy Interesante, etc.).
Traditionally, thermoelectric materials were envisaged to harvest waste heat from high-temperature industrial sources. In the work presented in ADVANCED ENERGY MATERIALS, we investigated if organic thermoelectrics can use sunlight as the heat source, without any further requirements such as e.g. vacuum insulation. Due to their low thermal conductivity, and broadband optical absorption, cellulose-nanotube composites turned out to be a particularly suited material for solar thermoelectric generators, be it stand-alone, or added on to regular solar cells to harness the otherwise wasted infrared radiation.
Farming thermoelectric paper
Deyaa Abol-Fotouh, Bernhard Dörling, Osnat Zapata-Arteaga, Xabier Rodríguez-Martínez, Andrés Gómez, J. Sebastian Reparaz, Anna Laromaine, Anna Roig, Mariano Campoy-Quiles
Energy & Environmental Science 12, 716-719, 2019
Solar Harvesting: a Unique Opportunity for Organic Thermoelectrics?
José P. Jurado, Bernhard Dörling, Osnat Zapata-Arteaga, Anna Roig, Agustín Mihi, Mariano Campoy-Quiles
Advanced Energy Materials 9, 1902385, 2019
Figure: Bacterials enable the concept of farming thermoelectric materials by growing free standing films of carbon nanotubes embedded within a bacterial cellulose matrix.