Periodic Reporting for period 3 - UncorrelaTEd (Solid-liquid thermoelectric systems with uncorrelated properties)
Período documentado: 2022-07-01 hasta 2024-06-30
More than 60% of the global power is lost as waste heat. Thermoelectric (TE) materials can convert heat into electricity and significantly contribute to the current energy challenge. Despite large efforts to identify better TE materials, the TE technology is limited by low efficiency. One of the two performance improvement routes, thermal conductivity reduction, has already reached its limit, which makes the other route, power factor (PF) improvements, crucial.
Current strategies targeting PF enhancements have only reached modest improvements, mainly due to the adverse interdependence of the Seebeck coefficient (S) and the electrical conductivity (σ), which produces a decrease in one of these properties if the other is increased. This is a serious obstacle to achieve the widespread application of the TE technology, since PF=σS^2.
UncorrelaTEd pursues the dream of breaking the S-σ correlation by introducing a new paradigm that comes from the connection of TEs and electrochemistry, using a properly designed hybrid system, formed by a porous TE solid permeated by a liquid electrolyte (ions in a liquid), as shown in Fig. 1. The porous solid and the liquid provide a low thermal conductivity, whereas the electrolyte tactically interacts with the solid to enlarge the PF. Unprecedented PF improvements have already been observed by UncorrelaTEd members in this system using a material with modest TE properties (Sb-doped SnO2). UncorrelaTEd aims at extending these improvements to different materials (bismuth telluride alloys, oxides, and polymers) with state-of-the-art TE properties, potentially leading to a powerful technology able to provide more than 4 times larger PFs than state-of-the-art low-mid temperature (<150 ºC) materials and ZTs>3.
Current strategies targeting PF enhancements have only reached modest improvements, mainly due to the adverse interdependence of the Seebeck coefficient (S) and the electrical conductivity (σ), which produces a decrease in one of these properties if the other is increased. This is a serious obstacle to achieve the widespread application of the TE technology, since PF=σS^2.
UncorrelaTEd pursues the dream of breaking the S-σ correlation by introducing a new paradigm that comes from the connection of TEs and electrochemistry, using a properly designed hybrid system, formed by a porous TE solid permeated by a liquid electrolyte (ions in a liquid), as shown in Fig. 1. The porous solid and the liquid provide a low thermal conductivity, whereas the electrolyte tactically interacts with the solid to enlarge the PF. Unprecedented PF improvements have already been observed by UncorrelaTEd members in this system using a material with modest TE properties (Sb-doped SnO2). UncorrelaTEd aims at extending these improvements to different materials (bismuth telluride alloys, oxides, and polymers) with state-of-the-art TE properties, potentially leading to a powerful technology able to provide more than 4 times larger PFs than state-of-the-art low-mid temperature (<150 ºC) materials and ZTs>3.
The main results of the project have been: (1) fabrication of solid-liquid systems with large PF improvements, (2) fabrication of porous films with good TE properties, (3) creation of an advanced simulator and (4) a new device concept potentially leading to ultra-high PFs.
1. Large PF improvements: They have been achieved with Sb:SnO2 combined with different electrolytes: (i) the Cr(acetylacetonate)3 complex dissolved in 3-methoxipropionitrile (3-MPN) provided x3.4 improvement, (ii) the polyelectrolyte poly(diallyl dimethylammonium chloride) provided x2.6 enhancement being a gel electrolyte, and (iii) the functionalization of the oxide with the viologen molecule [1,1’-bis(2-phosphonoethyl)-4,4´ bipyridinium dichloride] produced x2.5 improvements in an all-solid-state system.
Also, x2 PF improvements were achieved for n-type Ag-doped ZnO when contacted by the ionic liquid 1-butyl-3-methylimidazolium iodide (BMII), due to an increase of around 50% in the electrical conductivity without a change in the Seebeck coefficient. Moreover, the PF of p-type PEDOT:PSS was improved above x4 when treated with 0.1 M 4,4ʹ bipyridine in 1-ethyl-3-methylimidazolium bis(fluoromethylsulfonyl)imide (EMIMTFSI).
Unfortunately, no PF improvements were found for systems using bismuth telluride alloys as the TE material.
2. Fabrication of porous films with good TE properties: Different nanostructured TE materials were prepared in porous form with good TE properties. (i) Bismuth telluride alloys (both n- and p-type) were fabricated by electrophoretic deposition and solution-based routes. In addition, they were also prepared optimising cold press conditions (Fig. 2). (ii) Oxides, p-type V-doped Ca3Co4O9 and n-type Ag-doped ZnO were also obtained via hot press at reduced pressures (Fig. 3). (iii) P-type PEDOT:PSS films were also prepared by ice-templating method (Fig. 4).
3. Advanced simulator: An advanced Monte Carlo electronic transport simulator, which can take into consideration the complexities of the nanostructured and porous media were developed. The advanced simulator is available at the project website in open access.
4. A new concept, potentially leading to ultra-high PFs was identified from theoretical simulations. A patent application is in progress for its possible future exploitation. This system combines a porous TE solid with an electrolyte with certain composition.
All the project results were disseminated in a total of 35 contributions to conferences, 3 invited seminars and 12 scientific publications (at least 6 more in progress). Also, 3 PhD thesis were completed reporting project's results.
1. Large PF improvements: They have been achieved with Sb:SnO2 combined with different electrolytes: (i) the Cr(acetylacetonate)3 complex dissolved in 3-methoxipropionitrile (3-MPN) provided x3.4 improvement, (ii) the polyelectrolyte poly(diallyl dimethylammonium chloride) provided x2.6 enhancement being a gel electrolyte, and (iii) the functionalization of the oxide with the viologen molecule [1,1’-bis(2-phosphonoethyl)-4,4´ bipyridinium dichloride] produced x2.5 improvements in an all-solid-state system.
Also, x2 PF improvements were achieved for n-type Ag-doped ZnO when contacted by the ionic liquid 1-butyl-3-methylimidazolium iodide (BMII), due to an increase of around 50% in the electrical conductivity without a change in the Seebeck coefficient. Moreover, the PF of p-type PEDOT:PSS was improved above x4 when treated with 0.1 M 4,4ʹ bipyridine in 1-ethyl-3-methylimidazolium bis(fluoromethylsulfonyl)imide (EMIMTFSI).
Unfortunately, no PF improvements were found for systems using bismuth telluride alloys as the TE material.
2. Fabrication of porous films with good TE properties: Different nanostructured TE materials were prepared in porous form with good TE properties. (i) Bismuth telluride alloys (both n- and p-type) were fabricated by electrophoretic deposition and solution-based routes. In addition, they were also prepared optimising cold press conditions (Fig. 2). (ii) Oxides, p-type V-doped Ca3Co4O9 and n-type Ag-doped ZnO were also obtained via hot press at reduced pressures (Fig. 3). (iii) P-type PEDOT:PSS films were also prepared by ice-templating method (Fig. 4).
3. Advanced simulator: An advanced Monte Carlo electronic transport simulator, which can take into consideration the complexities of the nanostructured and porous media were developed. The advanced simulator is available at the project website in open access.
4. A new concept, potentially leading to ultra-high PFs was identified from theoretical simulations. A patent application is in progress for its possible future exploitation. This system combines a porous TE solid with an electrolyte with certain composition.
All the project results were disseminated in a total of 35 contributions to conferences, 3 invited seminars and 12 scientific publications (at least 6 more in progress). Also, 3 PhD thesis were completed reporting project's results.
The results achieved have demonstrated the possibility to significantly improve the PF of certain TE materials using electrolytes and also by surface functionalization. Unfortunately, these improvements did not take place in bismuth telluride materials and hence the expected high ZTs were not achieved, reducing the initially expected impact of the project. However, a significant amount of new knowledge has been achieved in this completely new area that aims at achieving improved TE performance by means of electrochemical strategies. This knowledge might serve in the future as the starting point for new research projects or innovations, being very promising the new concept identified by the theoretical simulations.