Project Portugal 2030

Summary

Currently much worldwide research is focused on clean and sustainable energy sources and efficient industrial processes that can respond to the rising energy demands of the world. The efficiency of energy use can be enhanced by thermoelectric (TE) harvesting of unused heat and by application of alternative methods in the industrial processes. TE materials directly convert temperature difference into electrical power via the Seebeck effect [1]. Dimensionless figure of merit (proportional to absolute temperature (T), electrical conductivity, square of Seebeck coefficient and inverse thermal conductivity) ZT, reaching 1, is an indicator of high-performance TE material for commercial applications [2]. Most of the current materials with ZT =1 such as chalcogenide and skutterudite compounds suffer from toxicity, mineral scarcity, and high cost, which are problems for universal application [3]. Their limitation to harvest electricity from solar, automotive, and industrial waste heat, due to decomposition and volatilization at elevated T [3] requires development of new, nontoxic, stable, naturally abundant, lightweight and low-cost materials based on oxides. While cobaltate-based oxide semiconductors of p-type, where holes serve as the main charge carriers, with ZT ~1 in high-T range have been found as very promising [4], n-type oxides with high electronic conductivity and equivalent ZT have yet to be discovered to produce effective p-n TE modules [2]. Conferring figure of merit ZT ~1 to n-type semiconductor oxides will enable their use in such low-cost, stable, and sustainable energy sources as thermoelectric (TE) generators, addressing the rising energy demands of the mankind at low CO2 emission. SUM EPOCH main goal is to prepare the oxides with enhanced TE performance, using fast and energy-efficient alternative sintering methods, and recognise the physical mechanisms of this enhancement with particular emphasis on the preparation conditions. Thus, the SUM EPOCH is an interdisciplinary project within fast-moving applied research fields of TE materials engineering and energy-efficient alternative sintering technology development together with the fundamental field of solid state physics. The SUM EPOCH concept is to use a multiscale approach that consists of: i) grain size engineering by Flash sintering and ultrafast high-temperature sintering at (sub-)micrometre level together with ii) reduced graphene oxide (rGO) addition at nanometre level and iii) Sr deficiency induced in Bi-, Gd- or Dy-doped and co-doped SrTiO3 (ST) materials at atomic level. The specific aims of the project are: 1. To develop ST-based n-type semiconductors by conventional and sol-gel methods 2. To hybridize donor-doped ST with reduced graphene oxide into novel composites 3. To define protocols for the sustainable fabrication of controlled-grain-size TE ceramics and composites using alternative sintering 4. To understand the preparation conditions-structure-microstructure-property relationships using advanced characterization of TE materials 5. To refine strategies for achievement of high-performance TE materials with further fabrication of a demonstrator device. If valid for ST, this concept together with synergetic development of energy-effective alternative sintering techniques can serve as a strategic platform to address the efficiency in other TE materials with further possible economic and social impacts, besides the scientific one.