Large-area and adaptable electrospun silicon-based thermoelectric nanomaterials with high energy conversion efficiencies

Abstract

Large amounts of waste heat generated in our fossil-fuel based economy can be converted into useful electric power by using thermoelectric generators. However, the low-efficiency, scarcity, high-cost and poor production scalability of conventional thermoelectric materials are hindering their mass deployment. Nanoengineering has proven to be an excellent approach for enhancing thermoelectric properties of abundant and cheap materials such as silicon. Nevertheless, the implementation of these nanostructures is still a major challenge especially for covering the large areas required for massive waste heat recovery. Here we present a family of nano-enabled materials in the form of large-area paper-like fabrics made of nanotubes as a cost-effective and scalable solution for thermoelectric generation. A case study of a fabric of p-type silicon nanotubes was developed showing a five-fold improvement of the thermoelectric figure of merit. Outstanding power densities above 100 W/m2 at 700 °C are therefore demonstrated opening a market for waste heat recovery.

Enhanced thermoelectric figure of merit of individual Si nanowires with ultralow contact resistances

“…These results are in a good position when comparing with similarly doped Si bottom-up NWs [43] and Si thin [20,55], possibly because of the low contact resistance and the high surface roughness of the present NWs, compared to smoother structures [44]. While other works reported more complex Si nanomaterials with higher doping and higher / (nano-bulk from [50,56] and nano-holes from [20,57]), to our knowledge, the present one is the first to report on the characterization of a nanomaterial which can be directly grown and integrated within MEMS using mature and scalable techniques. Other structures with remarkable performance also obtained by MEMScompatible procedures, like holey membranes, lack from a straightforward fabrication technique that allows to obtain them in suspended platforms [20], as is the case of the bottom-up NW arrays obtained in the present and related works [14][15][16][17]25,33].…”

“…Other structures with remarkable performance also obtained by MEMScompatible procedures, like holey membranes, lack from a straightforward fabrication technique that allows to obtain them in suspended platforms [20], as is the case of the bottom-up NW arrays obtained in the present and related works [14][15][16][17]25,33]. References from other works reporting ZT vs T values for bulk (solid line [3]) and nanostructures (dashed lines [50,56]) are included. The labels indicate the first author and the doping level in that work, in units of 10 19 B atoms/cm 3 .…”

Textile‐Based Thermoelectric Generators and Their Applications

“…a) The electrospun carbon nanofiber, b) poly‐silicon layer on the carbon nanofiber, c) silicon oxide nanotube after annealing of the carbon nanofiber, d) poly‐silicon layer coating the silicon oxide nanotube. Scale bars are 200 nm . Reproduced with permission from Ref .…”

“…[41] Unlike commonly used coating methods, Morata et al presented an industrially scalable manufacturing method for fabrication of large-area and cost-effective TE fabrics. [51] A case of TE fabric made up of p-type silicon nanotubes was fabricated by depositing silicon layers onto sacrificial substrates of electrospun carbon nanofibers. In a typical procedure, carbon nanofiber fabric was obtained from annealing as-electrospun PAN fabric ( Figure 4a).…”

“…The state-of-the-art TE materials with excellent thermoelectric properties at room temperature are bismuth telluride-based alloys. These inorganic [51] Reproduced with permission from Ref. [51] Copyright 2018 Nature Publishing Group.…”