CN115264964B

CN115264964B - Photo-thermal power conversion system and seawater desalination waste heat utilization system

Info

Publication number: CN115264964B
Application number: CN202210946238.8A
Authority: CN
Inventors: 石刚; 吴垚; 李赢; 王利魁
Original assignee: Jiangnan University
Current assignee: Jiangnan University
Priority date: 2022-08-08
Filing date: 2022-08-08
Publication date: 2023-11-10
Anticipated expiration: 2042-08-08
Also published as: CN115264964A

Abstract

The application discloses a photo-thermal electric conversion system and a seawater desalination waste heat utilization system, which comprise a thermal motor; the photo-thermal layer is in physical contact with the hot end of the thermoelectric machine and consists of a substrate, a photo-thermal material and an energy storage material, wherein the photo-thermal material and the energy storage material are formed on the substrate; and a waste energy collection layer in physical contact with the cold end of the thermoelectric machine. The photo-thermal electric conversion system has photo-thermal conversion, energy storage and heat transfer capabilities; due to the energy storage function, the system can continuously discharge in darkness, and meanwhile, the waste energy collecting layer in the system has excellent capability of utilizing waste energy by water evaporation due to the carbon foam with single-sided hydrophobicity.

Description

Photo-thermal power conversion system and seawater desalination waste heat utilization system

Technical Field

The application belongs to the technical field of waste energy utilization, and particularly relates to a photo-thermal electric conversion system and a seawater desalination waste heat utilization system.

Background

Currently, there are two main ways of converting solar energy into electrical energy. The first is a photovoltaic technology based on photo-generated electron-hole, which can efficiently convert solar energy into electric energy, but the conversion efficiency thereof decreases with the increase of the temperature of the photovoltaic panel. The other is based on photo-thermal technology that converts solar generated heat into electrical potential, which can produce both efficient electrical and thermal energy. The thermoelectric technology produces more stable electrical energy under a certain intensity of illumination relative to the PV.

The photo-thermal-electrical conversion process of solar thermoelectric generators (STEGs) is mainly based on the seebeck effect. And heating one end of the STEG by utilizing heat generated by sunlight, so that carriers diffuse from the hot end of the STEG to the cold end, accumulate at the cold end and further generate a potential difference. At present, STEGs can be roughly classified into two types from a material point of view. The first class of STEG is based on flexible organic thermoelectric materials, and the material has the characteristics of wide spectrum and high-intensity absorption of sunlight, and does not need to additionally add a solar energy absorber. It is noted that the organic thermoelectric material is applied in a thin film state, which cannot generate a significant temperature difference in the thickness direction, and thus thermoelectric conversion is achieved by a transverse temperature gradient of the thin film. The second category of STEGs is based on rigid inorganic thermoelectric materials, which need to be used in conjunction with solar absorbers and thermal management systems. The solar absorber converts incident solar radiation into heat, the thermoelectric generator converts the heat into a voltage differential, and the thermal management system removes waste heat from the thermoelectric generator. Common inorganic thermoelectric materials are bismuth telluride, silicon nanowires, oxide based materials, siGe alloys, respectively.

However, the waste heat transmitted by the first-type generator or the second-type generator is lost to the environment and is not fully utilized, so that the utilization efficiency of solar energy is only within 5%, and how to reuse the waste heat to improve the energy utilization efficiency is worth thinking. And the integration of the photo-thermal conversion system and the waste energy collection system is the key for solving the problem.

Disclosure of Invention

This section is intended to outline some aspects of embodiments of the application and to briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section as well as in the description of the application and in the title of the application, which may not be used to limit the scope of the application.

The present application has been made in view of the above and/or problems occurring in the prior art.

One of the purposes of the application is to provide a photo-thermal conversion system with excellent photo-thermal conversion performance.

In order to solve the technical problems, the application provides the following technical scheme: a photo-thermal electric conversion system is a hierarchical structure from top to bottom, which sequentially comprises a photo-thermal conversion system with energy storage capability, a thermoelectric conversion system with power generation capability and a waste energy collection layer with waste heat collection capability,

a heat motor;

the photo-thermal layer is in physical contact with the hot end of the thermoelectric machine and consists of a substrate, a photo-thermal material and an energy storage material, wherein the photo-thermal material and the energy storage material are formed on the substrate; the method comprises the steps of,

and the waste energy collecting layer is in physical contact with the cold end of the thermoelectric machine.

As a preferred embodiment of the photothermal conversion system of the present application, wherein: the substrate material comprises one or more of an intrinsic heat conducting polymer, a filled heat conducting polymer, heat conducting ceramic, heat conducting pure metal, heat conducting alloy, graphite, diamond, carbon nano tube, graphene, porous amorphous carbon, heat conducting silicone grease, heat conducting gel and heat conducting mica.

As a preferred embodiment of the photothermal conversion system of the present application, wherein: the substrate is porous and comprises a carbon component.

The substrate is porous, the porous substrate can provide a large surface area, and the light-heat conversion efficiency is improved by multiple scattering of light within the pores. The substrate may have at least 15% porosity, or at least 25% porosity, or at least 35% porosity, or at least 45% porosity. With the above-described number of holes, the solar energy absorption rate can be improved with a large surface area, and the generated steam can be easily discharged.

The substrate may include a carbon component, and when the substrate includes carbon, the photothermal conversion capability is excellent. The carbon-containing substrate comprises one or more of carbon foam, polyvinyl alcohol foam, polypyrrole foam, expanded graphite foam, and graphite flakes.

As a preferred embodiment of the photothermal conversion system of the present application, wherein: the photo-thermal material comprises one or more of conjugated polymer, carbon-based material, metal material based on local thermal effect formed by plasma resonance, semiconductor material based on non-radiative relaxation, black titanium compound, transition metal sulfide, transition metal oxide and biological photo-thermal molecule.

As a preferred embodiment of the photothermal conversion system of the present application, wherein: the energy storage material comprises one or more of higher aliphatic hydrocarbon compounds, fatty acid compounds, amide compounds, polyhydroxy carbonic acid compounds, polyolefin compounds, polycarboxylic aldehyde compounds, polyalcohol compounds, cellulose graft copolymers and derivatives, silane graft copolymers and derivatives, polyalcohols, paraffin, metal hydroxide, metal hydride, crystalline hydrated salts, metal carbonate, metal salt ammoniums, perovskite compounds, graphene, carbon nanotubes, carbon black and MXenes.

In some embodiments of the present application, the substrate, the photo-thermal material and the energy storage material are independent materials, and at this time, the optimal photo-thermal conversion efficiency can be obtained when the mass percentage of the photo-thermal material to the energy storage material is 1:20-10:1.

In other embodiments of the present application, some photothermal materials have both photothermal conversion and energy storage capabilities, and thus, the photothermal materials are used as photothermal materials and energy storage materials, such as carbon nanotubes, graphene, and the like.

As a preferred embodiment of the photothermal conversion system of the present application, wherein: the waste energy collecting layer is made of a single-side hydrophobic material, the hydrophobic side of the waste energy collecting layer is connected with the water supply assembly, and the non-hydrophobic side of the waste energy collecting layer is in physical contact with the cold end of the thermoelectric machine.

As a preferred embodiment of the photothermal conversion system of the present application, wherein: the waste energy collecting layer comprises a substrate and a hydrophobic layer, wherein the hydrophobic layer is physically coated or chemically modified on one side of the substrate.

As a preferred embodiment of the photothermal conversion system of the present application, wherein: the substrate is a porous material and comprises one or more of an intrinsic heat conducting polymer, a filled heat conducting polymer, heat conducting ceramic, heat conducting pure metal, heat conducting alloy, graphite, diamond, carbon nano tube, graphene, porous amorphous carbon, heat conducting silicone grease, heat conducting gel and heat conducting mica.

In one embodiment, the substrate of the waste energy collection layer is the same material as the substrate of the photo-thermal layer, such as carbon foam obtained from melamine foam by a two-step process.

As a preferred embodiment of the photothermal conversion system of the present application, wherein: the hydrophobic side of the waste energy collecting layer is connected with a water supply assembly, the water supply assembly can be cotton threads in a laboratory environment, and when the laboratory environment is specifically constructed, the hydrophobic side of the waste energy collecting layer is fully contacted with the water guide cotton threads, the waste energy collecting layer is placed on polyurethane foam with a hole in the center, and the water guide cotton threads penetrate through the polyurethane foam holes to be contacted with water in a beaker below.

As a preferred embodiment of the photothermal conversion system of the present application, wherein: the physical contact includes direct physical contact or bonding by a thermally conductive adhesive.

It is another object of the present application to provide a method for preparing a material for a photothermal layer in a photothermal conversion system according to any of the above-mentioned aspects, comprising,

providing a substrate;

assembling conductive polymer particles on a substrate by in situ oxidative polymerization;

the heat storage material is assembled to the surface of the conductive polymer particles by physical immersion deposition.

As a preferable scheme of the preparation method of the photo-thermal layer material in the photo-thermal electric conversion system, the application comprises the following steps: the provision of a substrate, in one embodiment using carbon foam as the substrate, the carbon foam being obtained from melamine foam by a two-step process; one specific method is as follows:

placing the flexible block melamine foam in a muffle furnace, stabilizing for 1-3 h in an air atmosphere at 250-300 ℃, then placing the treated melamine foam in a tubular furnace, and carbonizing for 10-60 min at 300-500 ℃ in a nitrogen atmosphere to prepare the carbon foam.

As a preferable scheme of the preparation method of the photo-thermal layer material in the photo-thermal electric conversion system, the application comprises the following steps: the assembly of conductive polymer particles on a substrate by in situ oxidative polymerization, in one embodiment the conductive polymer is polypyrrole, one specific method being:

the polypyrrole monomer and the carbon foam obtained by the method are combined in FeCl ₃ Stirring the mixture in the solution for 2 to 5 hours to obtain polypyrrole@carbon foam.

As a preferable scheme of the preparation method of the photo-thermal layer material in the photo-thermal electric conversion system, the application comprises the following steps: the heat storage material is assembled on the surface of the conductive polymer particles by physical impregnation deposition, and in one specific embodiment, the heat storage material adopts polyethylene glycol, specifically PEG 10000 with relative molecular weight of 10000, wherein one specific method is as follows:

heating polyethylene glycol to be completely melted, immersing the polypyrrole@carbon foam obtained by the method into polyethylene glycol melt, placing a sample in a vacuum oven for drying for 0.5-3 h, taking out the sample, and cooling to room temperature.

The application further aims to provide a sea water desalination waste heat utilization system, wherein a photo-thermal layer in the photo-thermal electric conversion system can convert solar energy into heat and then transfer the heat to the hot end of a TEG, an energy storage material in the photo-thermal layer can continuously provide heat for the TEG in darkness, and waste heat transferred by the TEG layer can be used for evaporating water for desalination, so that the solar energy utilization efficiency is improved, and the solar energy utilization system can also utilize the temperature difference of the cold side and the hot side of the TEG layer for power generation for electrochemical redox desalination; in particular to the preparation method of the composite material,

a photothermal conversion system as recited in any preceding claim; the method comprises the steps of,

and the electrodes at two ends of the electrochemical redox desalination device are respectively connected with the positive electrode and the negative electrode of a thermoelectric machine in the photo-thermal electric conversion system.

As a preferable scheme of the seawater desalination waste heat utilization system, the application comprises the following steps: the electrochemical redox desalination device adopts the prior art, can be disclosed in literature (ACS Sustainable chem. Eng.2019,7, 16182-16189), and specifically consists of carbon cloth, an electrolyte battery, an Anion Exchange Membrane (AEM), a Cation Exchange Membrane (CEM) and a salt circulation tank;

the positive pole and the negative pole of the thermal motor are respectively connected with the carbon cloth at the two ends of the desalination device through crocodile clamps.

Compared with the prior art, the application has the following beneficial effects:

the photo-thermal electric system obtained by the application has photo-thermal conversion, energy storage and heat transfer capability. Due to the energy storage function, the system can continuously discharge in darkness, and meanwhile, the waste energy collecting layer in the system has excellent capability of utilizing waste energy by water evaporation due to the carbon foam with single-sided hydrophobicity. When the photo-thermal electric system is applied to sea water desalination, the solar energy utilization efficiency is up to 86%, and if the evaporation energy of dark water is removed, the solar energy utilization efficiency is up to 59%, and sustainable work under intermittent illumination conditions is realized.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the description of the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art. Wherein:

FIG. 1 is a macroscopic photograph of each material in example 1 of the present application.

Fig. 2 is an SEM image of each material in example 1 of the present application.

FIG. 3 shows the ultraviolet absorption spectrum of each material in example 1 of the present application.

FIG. 4 is a thermal imaging temperature map of the PEG@PPy@CF material of example 1 of the present application at different illumination times.

Fig. 5 is an SEM image and EDS image of the waste energy collection layer material of example 2 of the present application.

Fig. 6 shows contact angles of both sides of the waste energy collecting layer material in example 2 of the present application.

FIG. 7 is a thermal image temperature map of the waste energy collecting layer material of example 2 of the present application at different illumination times.

Fig. 8 is a schematic structural diagram of the photo-thermal electric conversion system and the test thereof in embodiment 3 of the present application.

FIG. 9 is a graph showing the temperature of the light-to-heat conversion system at various locations in steady state in example 3 of the present application.

Fig. 10 is a schematic structural diagram of a seawater desalination waste heat utilization system in embodiment 4 of the present application.

FIG. 11 shows salt concentration before and after thermoelectric desalination of the seawater desalination waste heat utilization system in example 4 of the present application.

FIG. 12 shows the overall change in salt concentration of the concentrate and desalinate tanks recorded in example 4 of the present application.

Fig. 13 is a graph showing the results of a multiple cycle discharge test of the seawater desalination waste heat utilization system in embodiment 4 of the present application.

Fig. 14 shows the results of power generation performance test of TEG in the photo-thermal electric system prepared in examples 5, 6, and 7 of the present application.

FIG. 15 shows the results of water evaporation performance test of the photo-thermal electric systems prepared in examples 8, 9 and 10 of the present application.

FIG. 16 is a comparison of the performance of the photo-thermal electric system of comparative example 1 and that of example 3.

FIG. 17 is a comparison of the performance of the photo-thermal electric systems of comparative examples 2, 3, and 4 with that of example 3.

Detailed Description

In order that the above-recited objects, features and advantages of the present application will become more apparent, a more particular description of the application will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application, but the present application may be practiced in other ways other than those described herein, and persons skilled in the art will readily appreciate that the present application is not limited to the specific embodiments disclosed below.

Further, reference herein to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic can be included in at least one implementation of the application. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments.

Unless otherwise indicated, all starting materials used in the examples were commercially available.

Example 1

(1) Placing flexible block melamine foam (represented by MF) in a muffle furnace, stabilizing for 2 hours in an air atmosphere at 275 ℃, then placing the treated melamine foam in a tubular furnace, carbonizing for 30 minutes at 400 ℃ in a nitrogen atmosphere, and preparing a carbon foam named CF; the carbon foam was cut into cubes of 3cm by 4 cm.

(2) 0.746g FeCl was taken ₃ Dissolving in 50mL of water, stirring, standing and balancing for 1h, adding 0.1342g of polypyrrole (PPy) monomer under ice water bath, stirring together with the Carbon Foam (CF) obtained after cutting in the step (1), and controlling the stirring time to be 4h to obtain the carbon foam attached with polypyrrole particles, which is named as PPy@CF.

(3) Heating 1.0g of polyethylene glycol (PEG 10000) to 90 ℃ until the PEG is completely melted, immersing the PPy@CF obtained in the step (2) into the PEG melt at 90 ℃, placing the sample in a vacuum oven for drying for 1h, taking out the sample and cooling to room temperature to obtain the photo-thermal conversion material, which is named as PEG@PPy@CF.

Macroscopic photographs of MF, CF, ppy@cf and peg@ppy@cf materials are shown in fig. 1. Observing MF, CF, PPy@CF and PEG@PPy@CF materials through a field emission scanning electron microscope (SEM, hitachi S4800), wherein the microscopic morphology is shown in figure 2, and (a-1) and (a-2) are SEM images of MF; (b-1) and (b-2) are SEM images of CF; (c-1) and (c-2) are SEM images of PPy@CF; (d-1) and (d-2) are SEM images of PEG@PPy@CF.

As can be seen from FIG. 2, CF is obtained by calcining melamine foam MF under nitrogen atmosphere, and the 3D porous structure of the carbon foam is very close to that of melamine foam, as shown in FIGS. 2 (a-1), (a-2), (b-1) and (b-2), indicating that the calcination process does not destroy the material skeleton. Then, polypyrrole (ppy@cf) is assembled on the carbon foam skeleton by in-situ oxidative polymerization, and as can be seen from fig. 2 (c-1) and (c-2), the polypyrrole is in a granular shape, uniformly distributed on the surface of the carbon skeleton, and does not cause blocking of the skeleton and does not hinder heat transfer. Next, PEG was assembled to the polypyrrole surface (peg@ppy@cf) by physical immersion deposition, and as can be seen from fig. 2 (d-1) and (d-2), the carbon foam skeleton with polypyrrole particles attached to the surface was uniformly coated with PEG, and no significant accumulation in the pores was observed.

Diffuse reflectance UV-vis-IR absorption was measured on an ultraviolet-visible spectrophotometer (UV-3600 plus) for MF, CF, PPy@CF and PEG@PPy@CF materials, the ultraviolet absorption spectra of each material being shown in FIG. 3. As can be seen in fig. 3, carbonization of the foam and modification of PPy will increase the absorption of incident light, and introduction of PEG will slightly decrease the absorption of incident light.

The temperature of the sample under different illumination time is measured for the PEG@PPy@CF material by a thermal imaging instrument, the thermal imaging temperature is shown as a graph in fig. 4, the change of the surface temperature of the photo-thermal layer in the illumination process is recorded, and the photo-thermal layer reaches the equilibrium temperature of 87.6 ℃ after illumination for 10min, so that the photo-thermal layer has excellent heat storage performance and heat conduction performance.

Example 2

(2) Dissolving 2.0 mu L of fluoro silylation agent in 5mL of ethyl acetate, uniformly coating the solution on one side surface of the carbon foam CF obtained in the step (1) by using a suspension coater, controlling the suspension coating speed to be 1500rpm, soaking the treated foam in acetone and chloroform, ultrasonically cleaning and drying to form foam with hydrophobicity, and obtaining a waste energy collecting layer material named CF (-F).

SEM images of the waste energy collecting layer materials CF (-F) are shown in FIGS. 5 (a-1), (a-2). The waste energy collecting layer material consists of CF with single-sided hydrophobic modification, and EDS analysis of F element distribution is carried out on two sides of the CF (-F) material as shown in (b-1) and (b-2) of FIG. 5, wherein (b-1) is the non-hydrophobic surface of the CF (-F) material; (b-2) is a hydrophobic surface of CF (-F) material, and it can be seen that there is a distinct F element distribution at one end of the hydrophobic modification and no F element distribution at the other end, which further demonstrates that the foam is a single-sided hydrophobic structure.

The contact angle of both sides of the CF (-F) material was measured by an optical contact angle measuring instrument (OCA 40), and as shown in fig. 6, the contact angle of one end subjected to the fluorosilylation modification was 117.6 °, and the contact angle of the other end not subjected to any modification was 0 °. When the water droplets are at the hydrophobic end of the foam, the water is absorbed into the hydrophilic layer as the water droplets are subjected to an upward capillary force greater than the downward gravitational and hydrophobic forces. And when water is at the hydrophilic end of the foam, water is stored in the foam due to being subjected to an upward capillary force greater than the downward gravitational force. The single-sided hydrophobic structure can cool the heat motor by utilizing water stored in the foam on one hand, so that the power generation efficiency of the heat motor is improved, and on the other hand, the heat convection loss caused by water backflow at the top end of the foam can be reduced, so that the evaporation efficiency of the water is improved.

The temperature of the sample under different illumination time was measured for the CF (-F) material by a thermal imager, the thermal imaging temperature is shown in FIG. 7, the change of the side temperature of the waste energy collecting layer in the illumination process is recorded, and the waste energy collecting layer reaches the equilibrium temperature of 33 ℃ after illumination for 10 min.

Example 3

As shown in fig. 8 (a), embodiment 3 provides a photo-thermal conversion system, which comprises a photo-thermal layer 100, a thermoelectric machine 200 and a waste energy collecting layer 300 from top to bottom, wherein the lower surface of the photo-thermal layer 100 and the upper surface (hot end) of the thermoelectric machine 200 are bonded by a heat-conducting silica gel 101 to obtain peg@ppy@cf/TEG, and then the lower surface (cold end) of the thermoelectric machine 200 and the upper surface of the waste energy collecting layer 300 are in physical contact to obtain peg@ppy@cf/TEG/CF (-F).

The thermoelectric machine (TEG) is a commercial thermoelectric machine, and the model number of the thermoelectric machine is TEP1-142T300.

The specific construction method of the photo-thermal electric conversion system is as follows:

(1) The photothermal conversion material PEG@PPy@CF obtained in example 1 was cut into cubes of 3cm×3cm, and the thickness was controlled to be 0.2cm;

(2) Bonding the lower surface of the PEG@PPy@CF with the upper surface (hot end) of a thermal motor (TEG) through heat-conducting silica gel to obtain the PEG@PPy@CF/TEG;

(3) The waste energy collecting layer material CF (-F) obtained in example 2 was cut into cubes of 3cm X3 cm and the thickness was controlled to be 1.5cm;

(4) The lower surface (cold end) of the thermo-motor is brought into physical contact with the upper surface of CF (-F) to obtain PEG@PPy@CF/TEG/CF (-F).

In the test, as shown in fig. 8 (b), the bottom end of the waste energy collecting layer 300 was sufficiently contacted with the water guide cotton thread 301, and placed on the polyurethane foam 302 having a hole of 3mm in diameter in the center, and the water guide cotton thread 301 was contacted with water in the lower beaker 303 through the hole of the polyurethane foam 302.

The temperatures of different positions in the photo-thermal-electric conversion system under the steady state recorded by the thermal imager are respectively the surface temperature (a) of the photo-thermal layer, the top temperature (b) of the thermoelectric machine, the temperature (c) of the thermoelectric machine, the bottom temperature (d) of the thermoelectric machine, the temperature (e) of the waste energy collecting layer and the temperature (f) of the water body, which correspond to 60.4 ℃, 51.4 ℃, 38.4 ℃, 33.4 ℃, 32.5 ℃ and 22.6 ℃ respectively, and the temperatures decrease from top to bottom in sequence as shown in fig. 9.

From this phenomenon, the mechanism of heat transfer down the entire device was analyzed.

Assuming that the energy of the incident light is E and the heat reaching the photo-thermal layer is Q, a part of the heat Q is transferred to the TEG by heat conduction (Q1), a part of the heat Q is transferred to the air and dissipated by heat radiation and heat convection (QL 1), and the other part is PEG (E) ₁ ) Absorbing and storing. Part of the heat Q1 is transferred to the waste energy collection layer by heat conduction (Q2), part of the heat is transferred to the air by heat radiation and heat convection (QL 2) and dissipated, and the other part is used for power generation (E ₂ ). A part of the heat Q2 is used for evaporation of water (E ₃ ) One part of the heat is transferred to the air for dissipation by heat radiation and heat convection (QL 3), and the other part is transferred to the water loss convection (QL 4) in the body by heat conduction and heat transfer.

The important parameter in the whole conversion process is the solar energy utilization efficiencyThe calculation of (2) is shown in formulas (1) to (5).

E ₁ ＝M ₁ H ₁ (2)

E ₂ ＝VIt (3)

E ₃ ＝M ₂ H ₂ (4)

E＝Pt (5)

Wherein E is ₁ Is the energy stored by PEG; e (E) ₂ Is the electric energy for TEG desalination; e (E) ₃ Is the heat energy utilized by water evaporation; e refers to the total input energy of solar energy; m is M ₁ Is the mass of PEG 10000; h ₁ Is the phase transition enthalpy of PEG 10000; v refers to the operating voltage (redox desalination system); i refers to the operating current (redox desalination system); m is M ₂ Is the mass of the evaporated water; h ₂ Is the evaporation enthalpy of water; p refers to solar energy input power; t refers to the device on time. The relevant values for the energy efficiency calculations are shown in table 1.

Table 1 correlation values for energy efficiency calculations

The solar energy utilization efficiency is 86% through calculation, and if the evaporation energy of the dark environment water is removed in the calculation process, the solar energy utilization efficiency is 59%.

Example 4

As shown in fig. 10, the photothermal conversion system assembled in example 3 was used for redox desalination power supply, and a seawater desalination waste heat utilization system was constructed.

An electrochemical redox desalination device shown in fig. 10 consists of carbon cloth, electrolyte cells, anion Exchange Membranes (AEMs), cation Exchange Membranes (CEMs) and salt flow cells, specifically referred to (ACS sustaiable chem. Eng.2019,7, 16182-16189).

Two pieces of graphite paper are used as current collectors, [ Fe (CN) ₆ ] ^3-/4- As an anolyte and a catholyte, a salt stream is located between the AEM and CEM membranes. 4mL of 4mM/40mM [ Fe (CN) respectively ₆ ] ^3-/4- The electrolyte solution was flowed at a rate of 17.28mL/min in the anode and cathode chambers connected to each other using a hose, and then circulated back to the container; salt feed containing 1.5mL NaCl solution was circulated separately at 3000ppm per channel, [ Fe (CN) ₆ ] ^3-/4- The electrolyte and the two salt streams are driven by peristaltic pumps. Each compartment of the electrolyte or salt feed has a rectangular parallelepiped size with a thickness of 0.3cm and a thickness of 1.5x1.5 cm ² The sectional area, namely the effective area in the desalting process, is the silica gel material except that the two outermost acrylic plates.

The bottom end of the waste energy collecting layer CF (-F) of the photo-thermal electric system is fully contacted with a water guiding cotton thread which passes through the polyurethane foam hole and is contacted with water in a beaker below, and the water guiding cotton thread is placed on the polyurethane foam with a hole with the diameter of 3mm in the center. Finally, the positive and negative poles of the heat motor are respectively linked with the graphite paper poles at both ends of the desalination device by crocodile clips, as shown in fig. 10.

The salt concentration before and after the thermoelectric desalination was measured by a low-precision salinity meter, and as a result, as shown in FIG. 11, FIG. 11 (a) corresponds to the salt concentration before the thermoelectric desalination (3000 ppm), and FIGS. 11 (b) and 11 (c) correspond to the salt concentration in the concentration tank (3000 ppm) and the salt concentration in the desalination tank (3000 ppm), respectively, after 600 minutes of thermoelectric desalination; fig. 12 shows the overall change in concentration and desalination cell salt concentration recorded by a high-precision conductivity meter. The results indicated that after 600 minutes the concentration tank had a salt concentration of 428ppm and the desalination tank had a salt concentration of 5571ppm, the former being almost twice that of the latter, the salt concentration of the desalination tank being below the baseline of fresh water.

The cycle stability is an important index for evaluating the performance of photothermal and electric desalination, and a plurality of cycle discharge tests were performed in laboratory scale test, and the results are shown in fig. 13. Fig. 13 (a) and 13 (b) are graphs of the open circuit voltage and the short circuit current of the system over time during the cycling process, respectively, and only negligible fluctuation of each graph can be seen from the graph, which proves the circulability and stability of the system in laboratory scale testing.

Example 5

In this example, compared with example 3, when ppy@cf in the photovoltaic layer was prepared, the stirring time was controlled to be 2, 3, 4, 5 hours, respectively, and the other preparation process conditions were the same as in example 3.

The power generation performance of TEG in the photo-thermal electric system obtained in example 5 was tested, and the result is shown in fig. 14 (a).

Referring to fig. 14 (a), the effect of the synthesis time of PPy of different conductive polymers on the power generation performance of TEG is shown, while the effect of the synthesis time of PPy is the content of PPy of the conductive polymer, it can be seen from the graph that the lower content of PPy of the conductive polymer can weaken the absorption of near infrared light by peg@ppy@cf, thereby reducing the photo-thermal conversion efficiency of solar energy and reducing the output power of TEG; the polypyrrole with higher content can generate regional accumulation, poor contact with the carbon foam skeleton and obstruct heat transfer from PEG@PPy@CF to the hot surface of the thermoelectric machine, so that the output power of the thermoelectric machine is reduced, and when the polymerization time is 4 hours, the open circuit voltage reaches a peak value.

Example 6

In this example, compared with example 3, the thicknesses of the carbon foam in the photoelectric layer were controlled to be 0.1, 0.2, 0.5, 1.0, and 1.5cm, respectively, and the other production process conditions were the same as in example 3.

The power generation performance of TEG in the photo-thermal electric system obtained in example 6 was tested, and the result is shown in fig. 14 (b).

Referring to fig. 14 (b), the effect of photo-thermal layer thickness on TEG power generation performance is demonstrated, and as the carbon foam thickness increases, the open circuit voltage of TEG exhibits a law of increasing and then decreasing. When the thickness of the carbon foam is thicker, the longer heat transfer path can cause serious energy loss, so that the output power of the TEG is reduced; when the thickness of the carbon foam is relatively thin, the contents of the light absorbing material and the light-heat conversion material are insufficient, the light-heat conversion efficiency of solar energy is not good, and the output power of the heat motor is further reduced. The open circuit voltage peaks when the carbon foam thickness is 0.2 cm.

Example 7

In this example, compared with example 3, the addition amounts of PEG at the time of preparing PEG@PPy@CF were controlled to be 0.5 g, 1.0g, 1.5 g and 2.0g, respectively, and the other preparation process conditions were the same as in example 3.

The power generation performance of TEG in the photo-thermal electric system obtained in example 7 was tested, and the result is shown in fig. 14 (c).

Referring to fig. 14 (c), it can be seen that the open circuit voltage of TEG increases and then decreases with increasing PEG content. Because the phase change energy storage material PEG has the capability of storing energy and heat conductivity, the heat transfer channel can be enlarged by increasing the dosage of PEG, so that more heat can be transferred to the hot end of the TEG more quickly, and the stability and peak value of open-circuit voltage are improved; however, during the photo-thermal conversion of peg@ppy@cf, excessive PEG may leak, and more heat must be absorbed to reach energy storage saturation, delaying the open circuit voltage of the TEG to reach a steady state. Therefore, when the PEG content is as high as 1.5 and 2.0g, the open circuit voltage of TEG does not reach a peak value within 900s, and thus, the optimum PEG content is 1.0g, and the corresponding open circuit voltage reaches a peak value of 41mV within 900s, exhibiting excellent stability.

Example 8

In this example, compared with example 3, the thickness of the waste energy collecting layer was controlled to be 0.5, 1.0, 1.5, 2.0 and 2.5cm when constructing the photo-thermal electric system, and the other preparation process conditions were the same as in example 3.

The photo-thermal electric system obtained in example 8 was subjected to water evaporation performance test, and the results are shown in FIG. 15 (a).

Referring to fig. 15 (a), the effect of waste heat utilization rate of water evaporation by waste energy collecting layer thickness is demonstrated, and as the waste energy collecting layer CF (-F) thickness increases, the water evaporation rate exhibits a law of increasing and then decreasing. This is because the addition of CF (-F) thickness can expand its side area, which is beneficial to the escape of moisture, thereby increasing the moisture evaporation rate. However, when the CF thickness is too thick, insufficient water reaches the interface of CF (-F) and the TEG cold side, a part of the waste heat from the TEG cold side is used for ineffective heating, resulting in a decrease in the moisture evaporation rate.

Example 9

In this example, compared with example 3, when preparing the single-sided hydrophobically modified carbon foam in the waste energy collecting layer, the dipping amounts of the fluoro silylating agent were controlled to be 0.5, 1.0, 1.5, 2.0, 2.5 μl, respectively, and the other preparation process conditions were the same as those of example 3.

The photo-thermal electric system obtained in example 9 was subjected to water evaporation performance test, and the result is shown in FIG. 15 (b).

Referring to fig. 15 (b), as the amount of fluorine-containing agent increases, the water evaporation rate exhibits a law of increasing and then decreasing. The high concentration of fluorine (F) containing reagent can improve the hydrophobicity of the bottom of CF (-F), and the high hydrophobicity can prevent the heat convection loss caused by the water backflow heated by the waste heat of TEG, thereby improving the utilization efficiency of the waste heat evaporating water. However, too high hydrophobicity makes it difficult to transfer water from the bottom to the top of CF (-F), resulting in insufficient water supply, low waste heat utilization efficiency, and unfavorable acceleration of evaporation rate of water.

Example 10

In this example, compared with example 3, when preparing the single-sided hydrophobically modified carbon foam in the waste energy collection layer, the fluorine suspension coating speeds were controlled to be 500, 1000, 1500, 2000, 2500rpm, respectively, and the remaining preparation process conditions were the same as in example 3.

The photo-thermal electric system obtained in example 10 was subjected to water evaporation performance test, and the results are shown in FIG. 15 (c).

Referring to fig. 15 (c), as the spin coating rate decreases, the water evaporation rate exhibits a law of increasing and then decreasing. The low spin coating rate can improve the hydrophobicity of the bottom of the CF (-F), and the high hydrophobicity can prevent heat convection loss caused by water backflow heated by waste heat of the TEG, so that the utilization efficiency of waste heat evaporation water is improved. However, too high hydrophobicity makes it difficult to transfer water from the bottom to the top of CF (-F), resulting in insufficient water supply, low waste heat utilization efficiency, and unfavorable acceleration of evaporation rate of water.

Comparative example 1

Comparative example 1 in comparison with example 3, the non-hydrophobically modified carbon foam was used as waste energy collection layer material, and the remaining preparation process conditions were the same as example 3.

Referring to the test method of the above example, comparing the thermoelectric system prepared in the above comparative example with that of example 3, the results are shown in fig. 16, and fig. 16 (a) shows the open circuit voltage comparison of thermoelectric systems before and after modification by single-sided fluorine; FIG. 16 (b) is a TEG cold face temperature after optimization of the waste energy collection layer; FIG. 16 (c) is the TEG cold face temperature before optimization of the waste energy collection layer.

As can be seen from fig. 16, after the single-sided hydrophobically modified carbon foam is used as the waste energy collecting layer material, the temperature of the cold end of the TEG can be further reduced, thereby increasing the output power of the TEG.

Comparative example 2

In order to verify the contribution of the conductive polymer PPy to the photo-thermal electric system, the photo-thermal electric system does not contain the conductive polymer PPy as compared with example 3, and the other preparation process conditions are the same as in example 3.

Comparative example 3

In order to verify the contribution of the phase-change energy storage material PEG to the photo-thermal electric system, compared with example 3, the photo-thermal electric system does not contain the phase-change energy storage material PEG, and the rest of preparation process conditions are the same as those of example 3.

Comparative example 4

In order to verify the contribution of the waste energy collecting layer composed of the carbon foam with single-sided hydrophobic modification to the photo-thermal electric system, the photo-thermal electric system does not contain the waste energy collecting layer compared with example 3, and the rest of the preparation process conditions are the same as example 3.

Referring to the test method of the above example, the photo-thermal electric system prepared in the above comparative example was compared with that of example 3, and the results are shown in fig. 17.

FIG. 17 shows a PEG@PPy@CF/TEG/CF (-F), PEG@CF/TEG/CThe thermoelectric conversion system of F (-F), PPy@CF/TEG/CF (-F), PEG@PPy@CF is 1 KW.m ^-2 Performance under sunlight; wherein (a) is the mass change within 1 hour; (b) An open circuit voltage, (c) a short circuit current, and (e) a temperature difference between a photo-thermal layer and a thermoelectric machine; (d) Thermal imaging images of the temperature of each layer of the optoelectronic system, PEG@PPy@CF/TEG/CF (-F) (d-1), PEG@CF/TEG/CF (-F) (d-2), PPy@CF/TEG/CF (-F) (d-3), PEG@PPy@CF/TEG (d-4); (f) an ultraviolet visible spectrum of PEG@CF, PEG@PPy@CF; (g) The influence of PEG load on the continuous discharge performance of the thermoelectric machine under dark conditions is shown; (h) System stability for a chopper light photo-thermoelectric system; (i) Solar energy utilization efficiency of four light-heat-electricity systems.

As shown by curves A1 and A3 in fig. 17 (a), curves B1 and B3 in fig. 17 (B), and curves C1 and C3 in fig. 17 (C), the water volatilization rate, open circuit voltage, and short circuit current were all higher for the system with the conductive polymer PPy than for the system without PPy. Since PPy can absorb more incident light to convert more heat, the surface temperature of peg@ppy@cf/TEG/CF (-F) is significantly higher than peg@cf/TEG/CF (-F), as shown in fig. 17 (e), 17 (d-1), 17 (d-2), and 17 (F). Therefore, the PEG@PPy@CF/TEG/CF (-F) has higher photo-thermal layer temperature, and can transfer more heat to the TEG, thereby improving the water evaporation rate and the TEG output power.

As shown by curves A1 and A2 in fig. 17 (a), curves B1 and B2 in fig. 17 (B), and curves C1 and C2 in fig. 17 (C), the water volatilization rate, open circuit voltage, and short circuit current of the system with the phase change energy storage material PEG are all higher than those of the system without PEG, and the electrochemical stability is more excellent. This is because PEG has the ability to conduct heat, resulting in more heat transfer channels. Therefore, the temperature of the upper surface layer of the thermal motor in the PEG@PPy@CF/TEG/CF (-F) system is obviously higher than that of the upper surface layer of the thermal motor in the PPy@CF/TEG/CF (-F) system, so that the thermal energy is more beneficial to downwards transfer, and the power generation and water evaporation performances of the system are improved. The former thus transfers more heat to the hot side of the TEG than the latter, see fig. 17 (d-1) and 17 (d-3). Meanwhile, after the photo-thermal transition reaches equilibrium, the continuous discharge time of the thermoelectric machine in the PEG system is up to 250s under the shading condition compared with the continuous discharge time of the PEG system and the PEG system without the PEG system in the dark state, the continuous discharge time of the thermoelectric machine in the PEG system is far longer than the discharge time of the thermoelectric machine in the PEG system without the PEG system, and the voltage is quickly restored to the peak value after the illumination is restored, as shown in (g) of fig. 17. This is because PEG undergoes an enthalpy change and absorbs energy under illumination, whereas upon loss of illumination, PEG releases stored heat to power the thermoelectric machine. FIG. 17 (h) is a graph of the open circuit voltage versus time for PEG@PPy@CF/TEG/CF (-F) under chopped light, further demonstrating the excellent repeatable heat storage capacity of PEG.

As shown by curves A1 and A4 in fig. 17 (a), curves B1 and B4 in fig. 17 (B), and curves C1 and C4 in fig. 17 (C), the water volatilization speed, open circuit voltage, and short circuit current of the system with the waste energy collecting layer are all higher than those of the system without the waste energy collecting layer. This is because the waste energy collection layer CF contains a large number of holes for steam to escape, and the escape of steam takes away a large amount of heat. Thus, the temperature of the cold face of the thermoelectric machine with the waste energy collecting layer is obviously lower than that of the thermoelectric machine without the waste energy collecting layer, so that the temperature difference of the cold face and the hot face of the thermoelectric machine is improved, and the power generation performance of the thermoelectric machine is improved, as shown in fig. 17 (d-1) and 17 (d-4).

From the above discussion, it is clear that the synergy of the various parts in PEG@PPy@CF/TEG/CF (-F) fully utilizes solar energy, resulting in solar energy utilization efficiency as high as 86%, much higher than other samples, as shown in FIG. 17 (i). The system is combined with effective waste energy, and the solar energy utilization efficiency is higher than that of other work reports in the field of light-heat-electric field.

In conclusion, the photo-thermal electric system prepared by the application has photo-thermal conversion, energy storage and heat transfer capabilities. Because of the energy storage function, the system can continuously discharge in darkness, meanwhile, all parts in the phase change energy storage material PEG@PPy@CF/TEG/CF (-F) in the system can perform synergistic effect, the system is combined with effective waste energy, the solar energy utilization efficiency is up to 86 percent when the photo-thermal electric system is applied to sea water desalination, and if the dark state water evaporation energy is removed, the solar energy utilization efficiency is up to 59 percent, and sustainable work under intermittent illumination conditions is realized.

It should be noted that the above embodiments are only for illustrating the technical solution of the present application and not for limiting the same, and although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solution of the present application may be modified or substituted without departing from the spirit and scope of the technical solution of the present application, which is intended to be covered in the scope of the claims of the present application.

Claims

1. A photothermal electrical conversion system, characterized by: comprising the steps of (a) a step of,

a heat motor;

the waste energy collecting layer is in physical contact with the cold end of the thermoelectric machine; the waste energy collecting layer is made of a single-side hydrophobic material, the hydrophobic side of the waste energy collecting layer is connected with the water supply assembly, and the non-hydrophobic side of the waste energy collecting layer is in physical contact with the cold end of the thermoelectric machine.

2. The photothermal conversion system of claim 1, wherein: the substrate material comprises one or more of an intrinsic heat conducting polymer, a filled heat conducting polymer, heat conducting ceramic, heat conducting pure metal, heat conducting alloy, graphite, diamond, carbon nano tube, graphene, porous amorphous carbon, heat conducting silicone grease, heat conducting gel and heat conducting mica.

3. The photothermal conversion system according to claim 1 or 2, wherein: the photo-thermal material comprises one or more of conjugated polymer, carbon-based material, metal material based on local thermal effect formed by plasma resonance, semiconductor material based on non-radiative relaxation, black titanium compound, transition metal sulfide, transition metal oxide and biological photo-thermal molecule.

4. The optical to thermal conversion system according to claim 3, wherein: the energy storage material comprises one or more of higher aliphatic hydrocarbon compounds, fatty acid compounds, polyhydroxy carbonic acid compounds, polyolefin compounds, polycarboxylic aldehyde compounds, polyalcohol compounds, cellulose graft copolymers and derivatives, silane graft copolymers and derivatives, polyalcohol, paraffin, metal hydroxide, metal hydride, crystalline hydrated salt, metal carbonate, metal salt ammonia, graphene, carbon nano tube, carbon black, MXenes, azobenzene and ruthenium fulvalene.

5. The photothermal conversion system of any one of claims 1, 2, 4, wherein: the mass percentage of the photo-thermal material to the energy storage material is 1:20-10:1.

6. The photothermal conversion system of claim 5, wherein: the waste energy collecting layer comprises a substrate and a hydrophobic layer, wherein the hydrophobic layer is physically coated or chemically modified on one side of the substrate.

7. The photothermal conversion system of claim 6 wherein: the substrate is a porous material and comprises one or more of an intrinsic heat conducting polymer, a filled heat conducting polymer, heat conducting ceramic, heat conducting pure metal, heat conducting alloy, graphite, diamond, carbon nano tube, graphene, porous amorphous carbon, heat conducting silicone grease, heat conducting gel and heat conducting mica.

8. The photothermal conversion system of any one of claims 1, 2, 4, 6, 7, wherein: the physical contact includes direct physical contact or bonding by a thermally conductive adhesive.

9. A sea water desalination waste heat utilization system which is characterized in that: comprising the steps of (a) a step of,

the photothermal conversion system according to any one of claims 1 to 8; the method comprises the steps of,