Thermovoltaic material

Abstract

The invention relates to a thermovoltaic material: Thermovoltaic or thermoelectric materials are complex and rare, and therefore there was a need for a less costly thermovoltaic material; this aim is achieved by a silver colloid-treated amorphous anatase that builds up a voltage to carbon under the effect of heat.

Description

[0001] Description

[0002] TECHNICAL FIELD

[0003] The invention relates to a thermovoltaic material having an infrared radiation-induced electrical effect.

[0004] GENERAL STATE OF THE ART

[0005] Titanium dioxide, for example, can be coated with silver using physical vapor deposition (PVD) techniques - see INTERNATIONAL JOURNAL OF ADVANCED ELECTRONICS & COMMUNICATION SYSTEMS Approved by CSIR-NISCAIR ISSN NO: 2277-7318; ISSUE 5 VOL 3, OCT-NOV, 2014 PAPER ID 185-437-1-RV. It can then be used as a solar cell material, as the large band gap is reduced by this silver coating.

[0006] It was also shown in : TiO2 thin film coated with Silver (Ag) nano-particles for Solar cell application by Sandeep Kumar Singhl, Amlan Deep Borah, Janmoni Borah, Computer Science and Engineering, National Institute of Technology, Arunachal Pradesh, Itanagar, India, that titanium dioxide treated in this way exhibits a modified absorption spectrum in the visible (400 - 800 nm).

[0007] TiO2, which, unlike photoactive silicon, does not require complex crystallization or at least requires high purity and is available in large quantities as a white dye, is then suitable for use in low-cost photovoltaic solar cells.

[0008] In J. Mater. Chem. A, 2014, 2, Band gap engineered TiO2 nanoparticles for visible light induced photoelectrochemical and photocatalytic studies as well as Solar Energy Materials & Solar Cells 141 (2015) 162-170 “Silver nanoparticles and defect-induced visible light photocatalytic and photoelectrochemical performance of Ag@m-TiO2 nanocomposite” it is described that by electron beam treatment of titanium dioxide the otherwise large distance between the conduction bands can be reduced so that it absorbs in the visible range and can then decompose dyes. Otherwise the large band gap of (3.2 eV) of the anatase can only absorb relatively high-energy radiation and then use it to produce electrons. This band gap can be changed by complex doping, as shown by M. Khan et al. for photocatalytic studies, but also by electron beam (EB) assisted nanofabrication: J. Mater. Chem.A, 2014, 2, 637 “Band gap engineered TiO2 nanoparticles for visible light induced photoelectrochemical and photocatalytic studies”.

[0009] The processes previously used for doping or purely physical influence (electron beam) were complex. They resulted in TiO2 composites that were photoelectrically active in the visible range. While this complex treatment improved or enabled the absorption of solar radiation by narrowing the band gap, a large portion of the incident radiation spectrum was still not absorbed and remained ineffective when using these titanium dioxide cells.

[0010] It is clear that the sun provides a broader spectrum of radiation, of which only the UV portion up to a wavelength of 800 nm has been used to generate electrical energy. The near- and far-infrared portion remains completely unused.

[0011] It is therefore an object of the invention to improve the radiation absorption capacity of titanium dioxide so that a larger proportion of the incident electromagnetic radiation is absorbed and leads to the release of electrons.

[0012] According to the invention, the object is achieved by a titanium dioxide (anatase) mixed with colloidal silver.

[0013] Surprisingly, it was discovered that a cell made of dried, silver-treated titanium dioxide layered on graphite emitted electrons when exposed to infrared radiation, producing a voltage of around 3 V, which can be tapped in the usual way using conventional solar cell conductors. The material was largely electrically passive in direct sunlight, but in the dark at warm temperatures of around 30-40°C, it produced electricity from a cell structure as described below. It also turned out that the presence of water—also ensured by humectants—is essential for this thermoelectric effect. Dried-out titanium dioxide mixture layers did not produce any electricity, but could be induced to release electrons again by spraying them with water.

[0014] This cell arrangement—a graphite layer and a silver-treated anatase layer—showed little to no electrochemical activity in the visible range, but significantly more in the thermal radiation range. This means that a thermovoltaic cell was produced.

[0015] So far, such thermophotovoltaic cells are only available in expensive materials, e.g. GaAs, InP etc. (see https: / / www.ise.fraunhofer.de / de / geschaeftsfelder / photovoltaik / iii-v-und-konzentrator- photovoltaik / thermo-photovoltaik.html ):

[0016] Similar to solar energy generation using solar cells, thermophotovoltaics (TPV) converts radiant energy into electricity using photovoltaic cells. Unlike conventional solar cells, however, the radiant energy for electron production does not come from the visible spectrum, but is absorbed in the form of thermal radiation (long-wave photons). Special, complex-to-manufacture thermophotovoltaic cells made of absorber materials with band gaps in the infrared range can efficiently convert thermal radiation into electrical power.

[0017] In an energy system based on fluctuating renewable energy sources, thermophotovoltaic systems can make an important contribution to converting excess heat into electrical power. Such cells can also be combined with solar cells and then achieve significantly higher efficiency than conventional solar cells. TPV cells with high conversion efficiency are crucial for the overall efficiency (electrical-to-electrical). Furthermore, intelligent photon management is particularly essential – this is already being extensively investigated in the well-known, expensive indium or gallium thermovoltaic cells. For example, by integrating mirror layers into the TPV cell, photons that cannot be used for photovoltaic purposes can be reflected back onto the thermal emitter and thus recycled. This achieves high system efficiencies.Unfortunately, the research carried out so far is not yet economically viable due to the expensive and rare materials used, which also require high radiation temperatures.

[0018] It is therefore an object of the invention to provide a more readily available thermoelectric material.

[0019] This task is solved by the utility model.

[0020] Since anatase is industrially produced in large quantities as an amorphous white pigment, significant savings can be achieved compared to conventional materials. Furthermore, processing is simple and does not require toxic materials that require protective equipment and cause waste problems.

[0021] The thermovoltaic material used according to the invention comprises silver colloid-treated amorphous anatase. The advantage of this material, which is available in large quantities, is obvious. It is necessary that it contains water. For longer usability of the material, it is advantageous if it contains an electrically conductive humectant and / or is protected against drying out / evaporation.

[0022] It can be advantageous if it also contains glucose or other sugars. This acts as a humectant, but since it can be catalytically oxidized to gluconic acid in an electrochemical cell, it could actively participate in the processes in the thermovoltaic cell. In any case, its presence is advantageous.

[0023] The invention is explained below using exemplary embodiments and the following figure, to which it is in no way limited. The sole figure shows a schematic perspective view of a simple thermoelectric cell produced with the thermovoltaic material according to the invention.

[0024] DETAILED DESCRIPTION

[0025] The material according to the invention is prepared by initially mixing an aqueous silver colloid solution with deionized water; adding powdered anatase to this solution and thoroughly mixing the colloid solution with the powdered anatase. The resulting silver colloid-containing material is then air-dried—that is, it retains a low water content.

[0026] If necessary, a humectant, such as glucose, can be added to extend the functionality of a cell made with it. The photovoltaic material can also be resuspended or mixed with water as needed to restore its photovoltaic properties, which require some water.

[0027] The single figure schematically shows an arrangement that represents a typical application of the material in a thermoelectric cell. It comprises a flat graphite electrode 10, on which a coating of the thermoelectric material, silver colloid-treated anatase 12, with a humectant is applied, as well as a conventional solar electrode 14 for collecting the thermally generated electrons.

[0028] These measured cells were fabricated by suspending amorphous anatase in an aqueous silver colloid solution containing glucose as a humectant. This suspension was applied to a graphite foil and allowed to dry. The open-circuit voltage against the graphite layer could be measured on the air-dried anatase composite layer (i.e., with a water content secured by the glucose). Series connection of such cells was possible and yielded correspondingly higher voltage values.

[0029] A low zirconium oxide content of the anatase used showed no significant effect.

[0030] The open circuit voltage of this cell was very low at temperatures around zero - already at 22°C it was already active and delivered an open circuit voltage of around 0.37V - after warming up to about 80°C a greatly improved open circuit voltage was shown, which was dependent on the heating.

[0031] The measured voltage also depended on the silver concentration – with increasing silver colloid content of the dried anatase slurry, the measured open-circuit voltage increased. When measuring the open-circuit voltage of this simple thermovoltaic cell, in which one electrode is a graphite layer and the thermoelectric material dried on it releases electrons via a counter electrode, values ​​between 0.37 V for a single cell and 1.1 V for three series-connected cells were measured – depending on the cell area – at temperatures around 22°C. This means that even at these moderate temperatures, voltage can be produced from thermal radiation. A measurement in the dark in warm conditions yielded essentially the same values, while a measurement in the cold (around 0°C) yielded only unmeasurable voltage values.

[0032] Accordingly, the invention is a novel, inexpensively produced thermophotovoltaic material that can be used as a generator even at moderate temperatures.

[0033] Although only simple embodiments of the present utility model have been described in detail, a variety of alternative designs, applications and embodiments for implementing the utility model as defined by the scope of the claims will be apparent to a person skilled in the art.

Claims

Claims 1. Thermovoltaic material, characterized in that it comprises silver colloid-treated amorphous anatase.

2. Thermovoltaic material according to claim 1, further characterized by a water content.

3. Thermovoltaic material according to claim 1 or 2, characterized by an electrically conductive humectant.

4. Thermovoltaic material according to one of the preceding claims, characterized in that it comprises a sugar, in particular glucose.

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