Thermoelectric Performance Enhancement of n-type Chitosan-Bi2Te2.7Se0.3 Composite Films Using Heterogeneous Grains and Mechanical Pressure

Abstract

A cost-effective and sustainable approach was used to enhance the thermoelectric performance of printable thermoelectric composite films. Using this approach, we are trying to get rid of the highly energy-intensive (high temperature and long duration) and time-consuming process of manufacturing thermoelectric generators. This study presents a unique approach of using an environmental-friendly and naturally occurring binder, a heterogeneous particle size distribution and applied mechanical pressure to fabricate n-type thermoelectric composite films. Recently spotlighted biomaterial, chitosan, was employed as a binder and it provided enough binding strength to the composite thermoelectric films. Bi 2 Te 2.7 Se 0.3 is an attractive n-type thermoelectric material because of its high thermoelectric performance. In this work, we are using two different (100-mesh and 325-mesh) n-type Bi 2 Te 2.7 Se 0.3 thermoelectric conductive particles for thermoelectric composite films to understand the role of wide-range particle distribution on thermoelectric composite films. In addition, two different weight ratios (1:2000 and 1:5000) of binders to Bi 2 Te 2.7 Se 0.3 particle and two different applied pressures (150 MPa and 200 MPa) were used for this study. The application of pressure and the use of a heterogenous particle distribution improves the packing density which leads to well-aggregated and coalesced polycrystal bulk-like structure in chitosan 100-mesh (heterogeneous particle distribution) Bi 2 Te 2.7 Se 0.3 thermoelectric composite films and hence improves the overall electrical conductivity and power factor. The best performing composite film was made with an ink of a 1:2000 weight ratio of binder to100-mesh Bi 2 Te 2.7 Se 0.3 and the applied pressure was 200 MPa. The electrical conductivity was 200 ± 7 S cm À1 , the Seebeck coefficient was À201 ± 6 lV K À1 , the power factor was 808 ± 69.7 lW m À1 K À2 , the thermal conductivity was 0.6 W m À1 K À1 , and the figure of merit was 0.4 at room temperature. Using energy efficient, sustainable, and cost effective method we achieved ZT of 0.40 for n-type thermoelectric composite films which is comparable to other printed n-type TE composite films. A 2-leg n-type Bi 2 Te 2.7 Se 0.3 device was fabricated with a power output of 0.48 lW at a closed circuit voltage of 2.1 mV and DT of 12 K.

Stencil-Printed Scalable Radial Thermoelectric Device Using Sustainable Manufacturing Methods

“…Commercially available 100 mesh (a combination of micro-and nanometer-sized TE particles) n-type BTS and p-type BST TE powders were used to fabricate and characterize TE films [36][37][38][39]. An ink was synthesized by combining the TE powder with 0.5 wt.…”

“…These inks were then stencil printed onto Kevlar substrates using a customized stencil-printing mask (10 mm × 10 mm) and cured at 120 • C for 5 min until the solvent was evaporated. The resulting films were then hot-pressed for 30 min at 200 MPa and 200 • C using a Rosin Hot-press (TEGRIDY-3×10, Cannabis Hardware, Boynton Beach, FL, USA) [36][37][38][39]. The difference between the thickness of the substrate and the whole thickness was calculated using a Vernier caliper (293-340-30, Mitutoyo, Tokyo, Japan).…”

“…A Hall Effect measurement system (HMS-5500, ECOPIA, Neveda, Chandler Heights, Chandler, AZ, USA) was used to measure the in-plane, high-temperature electrical conductivity of the films. Both the high-temperature Seebeck setup and the accompanying Hall effect measurement system were described in our previous publications [37][38][39]. The measurements were performed at 25-100 • C. The Angstrom method was utilized to measure the in-plane directions for the thermal conductivity of the films.…”

“…Moreover, limited research has been performed on the varied shapes of flexible TEGs, e.g., circular or radial TEG devices, which can be used around waste heat pipes [25]. Therefore, to achieve widespread adoption of cost-effective and high-performance printed radial TEGs, it is important to implement a low thermal budget (low-temperature and short-curing duration) using additive manufacturing techniques [30][31][32][33][34][35][36][37][38][39].…”

“…In our previous work, we developed an energy-efficient curing method to stencil print a planar TEG device using [36][37][38]. The objective is to eliminate the high temperature and long-duration curing of the thermoelectric composites and TEGs and fabricate a highperformance radial TEG using a low thermal budget method, potentially used near waste heat pipes.…”