TiO_2−X based thermoelectric generators enabled by additive and layered manufacturing

Highlights: • Design and fabrication of TEGs for waste heat application. • Scalable and additive manufacturing demonstrated using thermal spray. • Multi-layer deposits composed of distinct functionality. • TEG produces 2.43 mW electrical power with a max efficiency of 0.85% (1.52 V). - Abstract: Traditional thermoelectric modules are acquired as separate components and then integrated by mechanical attachment into the engineering systems. There is, however, an interest and opportunity to manufacture thermoelectric device and basic electronics directly onto engineering structures. Recent studies have shown that plasma spray synthesized sub-stoichiometric titanium oxide (TiO_2−x) deposits show reasonable thermoelectric figure-of-merit, are capable of operating at relatively high temperatures (∼500 °C), and can be easily and cost effectively deposited onto both planar and cylindrical substrates over large areas with the capability to produce patterned and multilayer assemblies to optimize the power harvesting. This study demonstrates the fabrication and performance of such thermoelectric generators based on n-type TiO_2−x and Ni as the surrogate p-type and interconnect structures embedded within ceramic deposits. Up to 72 thermocouple modules were prepared incorporating both series and parallel connections to augment the performance resulting in a max efficiency of 0.85% for the couple and electric power of 2.43 mW at temperature of 723 K. Preliminary experiments were conducted with Li:Co₃O₄ as the p-type material with significant performance improvement. The methodologies described in this paper represents a potential pathway for large scale synthesis and fabrication of thermoelectric system directly in waste heat systems over large areas.