Abstract
Waste heat to electricity conversion using thermoelectric generators is emerging as a key technology in the forthcoming energy scenario. Carbon-based composites could unleash the as yet untapped potential of thermoelectricity by combining the low cost, easy processability, and low thermal conductivity of biopolymers with the mechanical strength and good electrical properties of carbon nanotubes (CNTs). Here we use bacteria in environmentally friendly aqueous media to grow large area bacterial nanocellulose (BC) films with an embedded highly dispersed CNT network. The thick films (≈10 μm) exhibit tuneable transparency and colour, as well as low thermal and high electrical conductivity. Moreover, they are fully bendable, can conformally wrap around heat sources and are stable above 500 K, which expands the range of potential uses compared to typical conducting polymers and composites. The high porosity of the material facilitates effective n-type doping, enabling the fabrication of a thermoelectric module from farmed thermoelectric paper. Because of vertical phase separation of the CNTs in the BC composite, the grown films at the same time serve as both the active layer and separating layer, insulating each thermoelectric leg from the adjacent ones. Last but not least, the BC can be enzymatically decomposed, completely reclaiming the embedded CNTs.
Highlights
Distributed sources of heat are ubiquitous, and about two thirds of all generated energy is lost in the form of heat
Bacterial cellulose is unique, as the composite film can be readily grown by culturing the bacteria in media that contain carbon nanotubes (CNTs), in situ forming composites that are intertwined at the nanoscale
We present a thermoelectric paper made of finely intermixed bacterial nanocellulose and carbon nanotube fibers
Summary
Distributed sources of heat are ubiquitous, and about two thirds of all generated energy is lost in the form of heat. Despite the magnitude of these numbers, this source of energy is not capitalized on because low-grade, distributed heat is unsuited for conventional heat engines. While some niche applications exist, the main reason preventing widespread adoption of thermoelectric generators is that they are commonly based on scarce and high-priced, often toxic, and brittle inorganic materials. Flexible and sustainable carbon based materials, which are less problematic concerning toxicity, could potentially become a viable alternative. Thermoelectric materials are rated using the dimensionless figure of merit, ZT = S2sT/k, where S is the Seebeck coefficient describing the voltage difference that builds up between the two sides of a material held at different temperatures, s is the electrical conductivity, k is the thermal conductivity and T is 716 | Energy Environ.
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