The authors acknowledge constructive discussion with Prof. D.Y.C. Leung and Dr. Y. Chen (The University of Hong Kong), Prof. M.H.K. Leung (City University of Hong Kong), Dr. W. S. Liu (Southern University of Science and Technology), and Mr. Frank H.T. Leung (Techskill [Asia] Limited). The authors acknowledge the financial support of General Research Fund of the Research Grants Council of Hong Kong Special Administrative Region, China, under Award Number 17204516 and 17206518, and Innovation and Technology Fund (Ref: ITS/171/16FX).

1. Preparation of the graphene oxide electrode
<ol>
	<li>Synthesis of graphene oxide via the modified Hummer&#39;s method
	<ol>
		<li>Steps 1.1.2 and 1.1.3 occur at a low temperature (&#60;0 &#176;C). Circulate ice water flowing through the external layer of a double wall glass beaker placed on a magnetic stirrer to create low temperature conditions for the reactants inside.</li>
		<li>Mix 1 g of sodium nitrate (NaNO3) with 100 mL of sulfuric acid (H2SO4, reagent grade, 95-98%) using slow stirring in the beaker.</li>
		<li>Add 1 g of flake graphite into the sulfuric acid and stir for 1 h in the cold bath. Add 6 g of potassium permanganate (KMnO4) gradually to the solution and stir the mixture for another 2 h.</li>
		<li>The next step of the reaction takes place at a middle temperature (~35 &#176;C). Change the ice water to 35 &#176;C water and continue the oxidation of the graphite by stirring for &#189; h.</li>
		<li>The last step of the reaction takes place at a TH (80-90 &#176;C). Add 46 mL of deionized (DI) water (70 &#176;C) into the reaction tank drop by drop. Note that that the reaction is strong. Add 140 mL of DI water and 20 mL of hydrogen peroxide (30% H2O2) in the reaction tank as the last step of the reaction. Make sure that golden particles of GO appear as a result.</li>
		<li>Wash the product thoroughly with dilute hydrochloric acid (HCl) and DI water several times until the GO suspension reaches pH = 7.</li>
		<li>Freeze the washed GO suspension overnight and dry it in a freeze dryer until water evaporates completely.</li>
	</ol>
	</li>
	<li>Preparation of the graphene oxide electrode
	<ol>
		<li>Mix the graphene oxide, carbon black, and PVDF in a mass ratio of 75:15:10 and put them in a glass bottle. Drip the solvent N-methyl-2-pyrrolidone (NMP) into the solid mixture and ensure the weight ratio of solvent and solid mixture is 4:1.</li>
		<li>Prepare the paste by mixing at 2,000 rpm for 13 min and defoaming in 1,200 rpm for 2 min with a mixer.</li>
		<li>Brush coat the paste on carbon paper until the coat is ~8-15 mg/cm2 and dry it for 4 h at 40 &#176;C.</li>
	</ol>
	</li>
</ol>
2. Preparation of the polyaniline (PANI) electrode
<ol>
	<li>Prepare 1 wt% carboxymethyl cellulose (CMC) aqueous solution by dissolving CMC powder in DI water by stirring for 10 h.</li>
	<li>Mix 50 mg of leucoemeraldine-base PANI and 10 mg of carbon black in a beaker. Add 150 &#956;L of 1 wt% CMC solution into the beaker and mix with a magnetic stirrer for 12 h.</li>
	<li>Add 6 &#956;L of 40% styrene-butadiene (SBR) solution into the mixture and stir for another 15 min.</li>
	<li>Place a piece of carbon paper on the doctor blade coater and drop the mixed PANI slurry at the leading edge of the carbon paper.</li>
	<li>Blade coat the slurry to produce a film 400 &#956;m thick on the carbon paper. Dry the coating for 4 h at 50 &#176;C.</li>
</ol>
3. Assembling the pouch cell
<ol>
	<li>Cut titanium foil into the approproate size and then connect each piece to a nickel tab with a 20 kHz ultrasonic spot welding machine.</li>
	<li>Place the porous hydrophilic polypropylene-based separator between the GO electrode and the PANI electrode to avoid short circuits. Each electrode is paired with one current collector.</li>
	<li>Package the electrodes using aluminum laminated film. Seal the sides of the aluminum laminated film with a compact vacuum sealer for 4 s. Set the temperature of the top and bottom sealing parts as 180 &#176;C and 160 &#176;C separately.</li>
	<li>Inject 500 &#956;L of the 1 M KCl electrolyte into the pouch cell and allow to equilibrate for 10 min.</li>
	<li>Extrude the excess electrolyte and seal the last side of the pouch cell in a -80 kPa vacuum chamber.</li>
</ol>
4. Setting up the temperature controlling system
<ol>
	<li>Stack the pouch cell between two thermoelectric modules. Place thermocouples on the top and bottom sides of the cell. Apply thermal paste to all the interfaces to ensure good thermal contact. 
	NOTE: The temperature is controlled with LabVIEW code. Temperatures measured from the thermocouples are compared with the setting temperatures and the output voltage is determined by the difference between the real time temperature and setting temperature via a PID control. The voltage signals are transmitted to the power supply and are connected to the thermoelectric module. The closed-loop control guarantees a temperature measurement accuracy within &#177; 0.5 &#176;C.</li>
</ol>
5. Electrochemical characterization
<ol>
	<li>Perform the electrochemical tests of the cell using a potentiostat. Conduct the thermal charging in open circuit mode while carrying out the electrical discharging process at a constant current.</li>
</ol>

<ol>
	<li>Chu, S., Majumdar, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Opportunities+and+Challenges+for+A+Sustainable+Energy+Future.">Opportunities and Challenges for A Sustainable Energy Future.</a> Nature. 488, 294 (2012).</li><li>Forman, C., Muritala, I. K., Pardemann, R., Meyer, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Estimating+the+Global+Waste+Heat+Potential.">Estimating the Global Waste Heat Potential.</a> Renewable and Sustainable Energy Reviews. 57, 1568-1579 (2016).</li><li>Gur, I., Sawyer, K., Prasher, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Searching+for+A+Better+Thermal+Battery.">Searching for A Better Thermal Battery.</a> Science. 335 (6075), 1454-1455 (2012).</li><li>He, R., Schierning, G., Nielsch, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thermoelectric+Devices:+A+Review+of+Devices,+Architectures,+and+Contact+Optimization.">Thermoelectric Devices: A Review of Devices, Architectures, and Contact Optimization.</a> Advanced Materials Technologies. 3 (4), 1700256 (2018).</li><li>Abraham, T. J., MacFarlane, D. R., Pringle, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+Seebeck+Coefficient+Redox+Ionic+Liquid+Electrolytes+for+Thermal+Energy+Harvesting.">High Seebeck Coefficient Redox Ionic Liquid Electrolytes for Thermal Energy Harvesting.</a> Energy &amp; Environmental Science. 6 (9), 2639-2645 (2013).</li><li>Zhang, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+Power+Density+Electrochemical+Thermocells+for+Inexpensively+Harvesting+Low-Grade+Thermal+Energy.">High Power Density Electrochemical Thermocells for Inexpensively Harvesting Low-Grade Thermal Energy.</a> Advanced Materials. 29 (12), 1605652 (2017).</li><li>Duan, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aqueous+Thermogalvanic+Cells+with+A+High+Seebeck+Coefficient+for+Low-Grade+Heat+Harvest.">Aqueous Thermogalvanic Cells with A High Seebeck Coefficient for Low-Grade Heat Harvest.</a> Nature Communications. 9 (1), 5146 (2018).</li><li>Im, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-Efficiency+Electrochemical+Thermal+Energy+Harvester+Using+Carbon+Nanotube+Aerogel+Sheet+Electrodes.">High-Efficiency Electrochemical Thermal Energy Harvester Using Carbon Nanotube Aerogel Sheet Electrodes.</a> Nature Communications. 7, 10600 (2016).</li><li>Hu, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Harvesting+Waste+Thermal+Energy+Using+A+Carbon-Nanotube-Based+Thermo-Electrochemical+Cell.">Harvesting Waste Thermal Energy Using A Carbon-Nanotube-Based Thermo-Electrochemical Cell.</a> Nano Letters. 10 (3), 838-846 (2010).</li><li>Poletayev, A. D., McKay, I. S., Chueh, W. C., Majumdar, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Continuous+Electrochemical+Heat+Engines.">Continuous Electrochemical Heat Engines.</a> Energy and Environmental Science. 11 (10), 2964-2971 (2018).</li><li>Qian, W., Li, M., Chen, L., Zhang, J., Dong, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Improving+Thermo-Electrochemical+Cell+Performance+by+Constructing+Ag-MgO-CNTs+Nanocomposite+Electrodes.">Improving Thermo-Electrochemical Cell Performance by Constructing Ag-MgO-CNTs Nanocomposite Electrodes.</a> RSC Advances. 5 (119), 97982-97987 (2015).</li><li>Lee, S. W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+Electrochemical+System+for+Efficiently+Harvesting+Low-Grade+Heat+Energy.">An Electrochemical System for Efficiently Harvesting Low-Grade Heat Energy.</a> Nature Communications. 5, 3942 (2014).</li><li>Yang, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Charging-Free+Electrochemical+System+for+Harvesting+Low-Grade+Thermal+Energy.">Charging-Free Electrochemical System for Harvesting Low-Grade Thermal Energy.</a> Proceedings of the National Academy of Sciences. 111 (48), 17011-17016 (2014).</li><li>Yang, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Membrane-Free+Battery+for+Harvesting+Low-Grade+Thermal+Energy.">Membrane-Free Battery for Harvesting Low-Grade Thermal Energy.</a> Nano Letters. 14 (11), 6578-6583 (2014).</li><li>Fukuzumi, Y., Amaha, K., Kobayashi, W., Niwa, H., Mortitomo, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prussian+Blue+Analogues+as+Promising+Thermal+Power+Generation+Materials.">Prussian Blue Analogues as Promising Thermal Power Generation Materials.</a> Energy Technology. 6 (10), 1865-1870 (2018).</li><li>Shibata, T., Fukuzumi, Y., Kobayashi, W., Moritomo, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thermal+Power+Generation+During+Heat+Cycle+Near+Room+Temperature.">Thermal Power Generation During Heat Cycle Near Room Temperature.</a> Applied Physics Express. 11 (1), 017101 (2018).</li><li>Shibata, T., Fukuzumi, Y., Moritomo, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thermal+Efficiency+of+A+Thermocell+Made+of+Prussian+Blue+Analogues.">Thermal Efficiency of A Thermocell Made of Prussian Blue Analogues.</a> Scientific Reports. 8 (1), 14784 (2018).</li><li>Takahara, I., Shibata, T., Fukuzumi, Y., Moritomo, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Improved+Thermal+Cyclability+of+Tertiary+Battery+Made+of+Prussian+Blue+Analogues.">Improved Thermal Cyclability of Tertiary Battery Made of Prussian Blue Analogues.</a> ChemistrySelect. 4 (29), 8558-8563 (2019).</li><li>Zhang, F., Liu, J., Yang, W., Logan, B. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Thermally+Regenerative+Ammonia-Based+Battery+for+Efficient+Harvesting+of+Low-Grade+Thermal+Energy+as+Electrical+Power.">A Thermally Regenerative Ammonia-Based Battery for Efficient Harvesting of Low-Grade Thermal Energy as Electrical Power.</a> Energy and Environmental Science. 8 (1), 343-349 (2015).</li><li>Zhu, X., Rahimi, M., Gorski, C. A., Logan, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Thermally-Regenerative+Ammonia-Based+Flow+Battery+for+Electrical+Energy+Recovery+from+Waste+Heat.">A Thermally-Regenerative Ammonia-Based Flow Battery for Electrical Energy Recovery from Waste Heat.</a> ChemSusChem. 9 (8), 873-879 (2016).</li><li>Zhang, F., LaBarge, N., Yang, W., Liu, J., Logan, B. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enhancing+Low-Grade+Thermal+Energy+Recovery+in+a+Thermally+Regenerative+Ammonia+Battery+Using+Elevated+Temperatures.">Enhancing Low-Grade Thermal Energy Recovery in a Thermally Regenerative Ammonia Battery Using Elevated Temperatures.</a> ChemSusChem. 8 (6), 1043-1048 (2015).</li></ol>

The authors declare no competing financial interests.

The aTEC converts thermal energy into electricity via a thermal charging process when heating from RT to TH and a successive electrical discharging process at TH. Getting rid of the dependence on a temperature gradient or a temperature cycle like the TGC and TREC, aTEC allows isothermal heating operation during the entire charging and discharging processes. Thermal induced voltage is based on the pseudocapacitive effect of GO because heating facilitates the chemisorption of protons on the oxygen fun...

Ubiquitous low-grade heat energy (&#60;100 &#176;C) could be recycled and converted into electricity1,2 but is instead wasted. Unfortunately, heat recovery is still a great challenge, because converting low-grade heat to electricity is usually inefficient due to the low temperature differential and the distributed nature of the heat sources3. Intensive research has been conducted in solid-state thermoelectric (TE) materials and devices for the past decades, but the scalable application of TE devices in a low-grade heat regime is limited by the low energy conversion efficiency (&#951;E) of &#60;2%4.
Alternative approaches based on the effect of temperature on electrochemical cells have been suggested as a solution to this problem, because the ionic Seebeck coefficient (&#945;) of thermoelectrochemical cells (TECs) is much higher than that of TE semiconductors5,6. Thermogalvanic cells (TGC) utilize redox active electrolytes sandwiched between two identical electrodes to generate a voltage across the cell when a thermal gradient is applied. The commonly used aqueous Fe(CN)63-/Fe(CN)64- electrolyte in TGCs was reported to have an &#945; of -1.4 mV/K and yield an &#951;E of &#60;1%7,8,9,10,11. However, TGCs suffer the drawback of the poor ionic conductivity of the liquid electrolyte, which is around three orders of magnitude smaller than the electronic conductivity in TE materials. The electric conductivity could be improved, but this improvement is always accompanied by a higher thermal conductivity, which leads to a lower temperature gradient. Therefore, the &#951;E of TGCs is inherently limited due to the trade-off between the liquid electrolyte conductance and the temperature requirement for the desired redox reactions in each side of the electrode.
A thermally regenerative electrochemical cycle (TREC)12,13,14 based on a battery system using a solid copper hexacyanoferrate (CuHCF) cathode and a Cu/Cu+ anode was recently reported. TREC is configured as a pouch cell to improve the electrolyte conductance, showing an &#945; of &#8722;1.2 mV/K and reaching a high &#951;E of 3.7% (21% of &#951;carnot) when operated at 60 &#176;C and 10 &#176;C. Nevertheless, one limit of TREC is that external electricity is required at the start of the process to charge the electrodes in each thermal cycle, leading to complicated system designs14. A TREC without this limitation can be achieved, but it suffers from a poor conversion efficiency of &#60;1%13. The TREC system demonstrates that a sodium-ion secondary battery (SIB)-type thermocell consisting of two types of Prussian blue analogues (PBA) with different &#945; values can harvest waste heat. The thermal efficiency (&#951;) increases proportionally with &#916;T. Moreover, &#951; reaches 1.08%, 3.19% at &#916;T = 30 K, 56 K separately. The thermal cyclability is improved using Ni-substituted PBA15,16,17,18.
Alternatively, a thermally regenerative ammonia battery (TRAB) employs copper-based redox couples [Cu(NH3)42+/Cu and Cu(II)/Cu] that operate with the reverse temperature gradient by switching the temperature of electrolyte co-operated with positive and negative electrodes, which produces a &#951;E of 0.53% (13% of &#951;carnot). However, this system is configured with two tanks full of liquid electrolyte, causing sluggish heating and cooling. Also, the ammonia stream in the system creates concerns regarding safety, leakage, and stability19,20,21.
Here we present an asymmetric thermoelectrochemical cell (aTEC) for heat-to-electricity conversion that can be thermally charged and electrically discharged by continuous isothermal heating without maintaining a temperature gradient in a geometric configuration or switching temperatures in a thermal cycle. The aTEC uses asymmetric electrodes, including a graphene oxide (GO) cathode and a polyaniline (PANI) anode, and KCl as the electrolyte. It is thermally charged via the thermo-pseudocapacitive effect of GO and then discharged with the oxidation reaction of PANI. Notably, the aTEC exhibits a high &#945; of 4.1 mV/K and attains a &#951;E of 3.32%, the highest ever achieved at 70 &#176;C (25.3% of &#951;Carnot).

<table><tbody><tr><td>Alumina laminated film</td><td>Showa Denko</td><td>SPALF C4</td><td></td></tr><tr><td>Carbon black</td><td>Alfa Aesar</td><td>H30253.22</td><td></td></tr><tr><td>Carbon paper</td><td>CeTech Co. Ltd</td><td>W0S1009</td><td></td></tr><tr><td>Carboxymethyl cellulose (CMC)</td><td>Guidechem company</td><td></td><td></td></tr><tr><td>DC Power supply</td><td>B&amp;amp;K Precision</td><td>Model 913-B</td><td></td></tr><tr><td>Doctor blade coater</td><td>Shining Energy Co. Ltd</td><td></td><td></td></tr><tr><td>Gamry</td><td>Gamry Instruments</td><td>Reference 3000</td><td></td></tr><tr><td>Graphite</td><td>Sigma-Aldrich</td><td>332461-2.5KG</td><td></td></tr><tr><td>Mixer</td><td>Thinky</td><td>ARE-250</td><td></td></tr><tr><td>Nickel tab</td><td>Tianjin Iversonchem company</td><td></td><td>4 mm width</td></tr><tr><td>N-Methyl-2-pyrrolidone (NMP)</td><td>Sigma-Aldrich</td><td>443778-1L</td><td></td></tr><tr><td>Polyaniline (leucoemeraldine base)</td><td>Sigma-Aldrich</td><td>530670-5G</td><td></td></tr><tr><td>potassium permanganate (KMnO4)</td><td>Sigma-Aldrich</td><td>223468-500G</td><td></td></tr><tr><td>Separator</td><td>CLDP</td><td></td><td>25 um thickness</td></tr><tr><td>Sodium nitrate (NaNO3)</td><td>Sigma-Aldrich</td><td>S5506-250G</td><td></td></tr><tr><td>Styrene butadiene</td><td>Tianjin Iversonchem company</td><td>BM400</td><td></td></tr><tr><td>Sulfuric acid</td><td>Sigma-Aldrich</td><td>320501-2.5L</td><td></td></tr><tr><td>Thermoelectric modules</td><td>CUI Inc.</td><td>CP455535H</td><td></td></tr><tr><td>Titanum foil</td><td>Qingyuan metal</td><td></td><td>0.03 mm thickness</td></tr></tbody></table>

asymmetric thermoelectrochemical cell for harvesting low-grade heat under isothermal operation

Low-grade heat is abundantly available in the environment as waste heat. The efficient conversion of low-grade heat into electricity is very difficult. We developed an asymmetric thermoelectrochemical cell (aTEC) for heat-to-electricity conversion under isothermal operation in the charging and discharging processes without exploiting the thermal gradient or the thermal cycle. The aTEC is composed of a graphene oxide (GO) cathode, a polyaniline (PANI) anode, and 1M KCl as the electrolyte. The cell generates a voltage due to the pseudocapacitive reaction of GO when heating from room temperature (RT) to a high temperature (TH, ~40-90 &#176;C), and then current is successively produced by oxidizing PANI when an external electrical load is connected. The aTEC demonstrates a remarkable temperature coefficient of 4.1 mV/K and a high heat-to-electricity conversion efficiency of 3.32%, working at a TH = 70 &#176;C with a Carnot efficiency of 25.3%, unveiling a new promising thermoelectrochemical technology for low-grade heat recovery.

The aTEC pouch cell was configured with asymmetric electrodes consisting of a GO cathode, a PANI anode, and filled with the KCl electrolyte. The thickness of the pouch cell shown in Figure 1A is 1 mm, which facilitates isothermal conditions between the two electrodes as well as efficient heat conduction. The scanning electron microscopy (SEM) images of the GO cathode and the PANI anode coated on carbon paper are shown in ...

Watch this Scientific Journal Video about Asymmetric Thermoelectrochemical Cell for Harvesting Low-grade Heat under Isothermal Operation at JoVE.com

Asymmetric Thermoelectrochemical Cell for Harvesting Low-grade Heat under Isothermal Operation

Low-grade heat is abundant, but its efficient recovery is still a great challenge. We report an asymmetric thermoelectrochemical cell using graphene oxide as a cathode and polyaniline as an anode with KCl as the electrolyte. This cell works under isothermal heating, exhibiting a high heat-to-electricity conversion efficiency in low-temperature regions.

Low-grade heat is abundantly available in the environment as waste heat. The efficient conversion of low-grade heat into electricity is very difficult. We ...

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6.8K Views.  University of Hong Kong. Lage kwaliteit warmte is overvloedig, maar efficiënte low-grade warmteterugwinning is nog steeds een grote uitdaging. Hier stellen we een asymmetrische thermische cel voor met een hoge energie-efficiëntie van meer dan 3%De asymmetrische thermische cel wordt thermisch geladen en elektrisch ontladen onder isothermale werking, dus het heeft potentieel voor verschillende toepassingen, vanwege zijn flexibiliteit, lage kosten en licht gewicht. De prestaties van asymmetrische thermische cel zijn s...

Video: Asymmetric Thermoelectrochemical Cell for Harvesting Low-grade Heat under Isothermal Operation

Synthesis of Non-uniformly Pr-doped SrTiO3 Ceramics and Their Thermoelectric Properties

We demonstrate a novel synthesis strategy for the preparation of Pr-doped SrTiO3 ceramics via a combination of solid state reaction and spark plasma sintering techniques. Polycrystalline ceramics possessing a unique morphology can be achieved by optimizing the process parameters, particularly spark plasma sintering heating rate. The phase and morphology of the synthesized ceramics were investigated in detail using X-ray diffraction, scanning electron microcopy and energy-dispersive X-ray spectroscopy. It was observed that the grains of these bulk Pr-doped SrTiO3 ceramics were enhanced with Pr-rich grain boundaries. Electronic and thermal transport properties were also investigated as a function of temperature and doping concentration. Such a microstructure was found to give rise to improved thermoelectric properties. Specifically, it resulted in a significant improvement in carrier mobility and the thermoelectric power factor. Simultaneously, it also led to a marked reduction in the thermal conductivity. As a result, a significant improvement (> 30%) in the thermoelectric figure of merit was achieved for the whole temperature range over all previously reported maximum values for SrTiO3-based ceramics. This synthesis demonstrates the steps for the preparation of bulk polycrystalline ceramics of non-uniformly Pr-doped SrTiO3.

Synthesis of Non-uniformly Pr-doped SrTiO3 Ceramics and Their Thermoelectric Properties

A protocol for the synthesis and processing of polycrystalline SrTiO3 ceramics doped non-uniformly with Pr is presented along with the investigation of their thermoelectric properties.

We demonstrate a novel synthesis strategy for the preparation of Pr-doped SrTiO3 ceramics via a combination of solid state reaction and spark plasma ...

A Gusseted Thermogradient Table to Control Soil Temperatures for Evaluating Plant Growth and Monitoring Soil Processes

Thermogradient tables were first developed in the 1950s primarily to test seed germination over a range of temperatures simultaneously without using a series of incubators. A temperature gradient is passively established across the surface of the table between the heated and cooled ends and is lost quickly at distances above the surface. Since temperature is only controlled on the table surface, experiments are restricted to shallow containers, such as Petri dishes, placed on the table. Welding continuous aluminum vertical strips or gussets perpendicular to the surface of a table enables temperature control in depth via convective heat flow. Soil in the channels between gussets was maintained across a gradient of temperatures allowing a greater diversity of experimentation. The gusseted design was evaluated by germinating oat, lettuce, tomato, and melon seeds. Soil temperatures were monitored using individual, battery-powered dataloggers positioned across the table. LED lights installed in the lids or along the sides of the gradient table create a controlled temperature chamber where seedlings can be grown over a range of temperatures. The gusseted design enabled accurate determination of optimum temperatures for fastest germination rate and the highest percentage germination for each species. Germination information from gradient table experiments can help predict seed germination and seedling growth under the adverse soil conditions often encountered during field crop production. Temperature effects on seed germination, seedling growth, and soil ecology can be tested under controlled conditions in a laboratory using a gusseted thermogradient table.

Traditional thermogradient tables create a range of temperatures across the surface. Welding gussets perpendicular to the surface of a thermogradient table will control temperature in depth increasing possible research applications.

Thermogradient tables were first developed in the 1950s primarily to test seed germination over a range of temperatures simultaneously without using a ...

Environment

Making Record-efficiency SnS Solar Cells by Thermal Evaporation and Atomic Layer Deposition

Tin sulfide (SnS) is a candidate absorber material for Earth-abundant, non-toxic solar cells. SnS offers easy phase control and rapid growth by congruent thermal evaporation, and it absorbs visible light strongly. However, for a long time the record power conversion efficiency of SnS solar cells remained below 2%. Recently we demonstrated new certified record efficiencies of 4.36% using SnS deposited by atomic layer deposition, and 3.88% using thermal evaporation. Here the fabrication procedure for these record solar cells is described, and the statistical distribution of the fabrication process is reported. The standard deviation of efficiency measured on a single substrate is typically over 0.5%. All steps including substrate selection and cleaning, Mo sputtering for the rear contact (cathode), SnS deposition, annealing, surface passivation, Zn(O,S) buffer layer selection and deposition, transparent conductor (anode) deposition, and metallization are described. On each substrate we fabricate 11 individual devices, each with active area 0.25 cm2. Further, a system for high throughput measurements of current-voltage curves under simulated solar light, and external quantum efficiency measurement with variable light bias is described. With this system we are able to measure full data sets on all 11 devices in an automated manner and in minimal time. These results illustrate the value of studying large sample sets, rather than focusing narrowly on the highest performing devices. Large data sets help us to distinguish and remedy individual loss mechanisms affecting our devices.

Tin sulfide (SnS) is a candidate material for Earth-abundant, non-toxic solar cells. Here, we demonstrate the fabrication procedure of the SnS solar cells employing atomic layer deposition, which yields 4.36% certified power conversion efficiency, and thermal evaporation which yields 3.88%.

Tin sulfide (SnS) is a candidate absorber material for Earth-abundant, non-toxic solar cells. SnS offers easy phase control and rapid growth by congruent ...

Engineering

Experimental System of Solar Adsorption Refrigeration with Concentrated Collector

To improve the performance of solar adsorption refrigeration, an experimental system with a solar concentration collector was set up and investigated. The main components of the system were the adsorbent bed, the condenser, the evaporator, the cooling sub-system, and the solar collector. In the first step of the experiment, the vapor-saturated bed was heated by the solar radiation under closed conditions, which caused the bed temperature and pressure to increase. When the bed pressure became high enough, the bed was switched to connect to the condenser, thus water vapor flowed continually from the bed to the condenser to be liquefied. Next, the bed needed to cool down after the desorption. In the solar-shielded condition, achieved by aluminum foil, the circulating water loop was opened to the bed. With the water continually circulating in the bed, the stored heat in the bed was took out and the bed pressure decreased accordingly. When the bed pressure dropped below the saturation pressure at the evaporation temperature, the valve to the evaporator was opened. A mass of water vapor rushed into the bed and was adsorbed by the zeolite material. With the massive vaporization of the water in the evaporator, the refrigeration effect was generated finally. The experimental result has revealed that both the COP (coefficient of the performance of the system) and the SCP (specific cooling power of the system) of the SAPO-34 zeolite was greater than that of the ZSM-5 zeolite, no matter whether the adsorption time was longer or shorter. The system of the SAPO-34 zeolite generated a maximum COP of 0.169.

With solar energy as the driving force, a novel adsorption refrigeration system has been developed and experimentally investigated. Water vapor and zeolite formed the working pair of the adsorption system. This manuscript describes the setup of the experimental rig, the operation procedure, and the important results.

To improve the performance of solar adsorption refrigeration, an experimental system with a solar concentration collector was set up and investigated. The ...

High-resolution Thermal Micro-imaging Using Europium Chelate Luminescent Coatings

Micro-electronic devices often undergo significant self-heating when biased to their typical operating conditions. This paper describes a convenient optical micro-imaging technique which can be used to map and quantify such behavior. Europium thenoyltrifluoroacetonate (EuTFC) has a 612 nm luminescence line whose activation efficiency drops strongly with increasing temperature, due to T-dependent interactions between the Eu3+ ion and the organic chelating compound. This material may be readily coated on to a sample surface by thermal sublimation in vacuum. When the coating is excited with ultraviolet light (337 nm) an optical micro-image of the 612 nm luminescent response can be converted directly into a map of the sample surface temperature. This technique offers spatial resolution limited only by the microscope optics (about 1 micron) and time resolution limited by the speed of the camera employed. It offers the additional advantages of only requiring comparatively simple and non-specialized equipment, and giving a quantitative probe of sample temperature.

Europium thenoyltrifluoroacetonate (EuTFC) has an optical luminescence line at 612 nm, whose activation efficiency decreases strongly with temperature. If a sample coated with a thin film of this material is micro-imaged, the 612 nm luminescent response intensity may be converted into a direct map of sample surface temperature.

Micro-electronic devices often undergo significant self-heating when biased to their typical operating conditions. This paper describes a convenient ...

Pool-Boiling Heat-Transfer Enhancement on Cylindrical Surfaces with Hybrid Wettable Patterns

In this study, pool-boiling heat-transfer experiments were performed to investigate the effect of the number of interlines and the orientation of the hybrid wettable pattern. Hybrid wettable patterns were produced by coating superhydrophilic SiO2 on a masked, hydrophobic, cylindrical copper surface. Using de-ionized (DI) water as the working fluid, pool-boiling heat-transfer studies were conducted on the different surface-treated copper cylinders of a 25-mm diameter and a 40-mm length. The experimental results showed that the number of interlines and the orientation of the hybrid wettable pattern influenced the wall superheat and the HTC. By increasing the number of interlines, the HTC was enhanced when compared to the plain surface. Images obtained from the charge-coupled device (CCD) camera indicated that more bubbles formed on the interlines as compared to other parts. The hybrid wettable pattern with the lowermost section being hydrophobic gave the best heat-transfer coefficient (HTC). The experimental results indicated that the bubble dynamics of the surface is an important factor that determines the nucleate boiling.

Pool-boiling heat-transfer experiments were carried out to observe the effects of hybrid wettable patterns on the heat-transfer coefficient (HTC). The parameters of investigation are the number of interlines and the pattern orientation of the modified wettable surface.

In this study, pool-boiling heat-transfer experiments were performed to investigate the effect of the number of interlines and the orientation of the ...

In Situ Surface Temperature Measurement in a Conveyor Belt Furnace via Inline Infrared Thermography

Measuring the surface temperature of objects that are processed in conveyor belt furnaces is an important tool in process control and quality assurance. Currently, the surface temperature of objects processed in conveyor belt furnaces is typically measured via thermocouples. However, infrared (IR) thermography presents multiple advantages compared to thermocouple measurements, as it is a contactless, real-time, and spatially resolved method. Here, as a representative proof-of-concept example, an inline thermography system is successfully installed into an IR lamp powered solar firing furnace, which is used for the contact firing process of industrial Si solar cells. This protocol describes how to install an IR camera into a conveyor belt furnace, conduct a customer correction of a factory calibrated IR camera, and perform the evaluation of spatial surface temperature distribution on a target object.

This protocol describes how to install an infrared camera into a conveyor belt furnace, conduct a customer correction of a factory calibrated IR camera, and evaluate the spatial surface temperature distribution of an object of interest. The example objects are industrial silicon solar cells.

Measuring the surface temperature of objects that are processed in conveyor belt furnaces is an important tool in process control and quality assurance. ...

Deposition of Bi2Te3 and Sb2Te3 Thin Films on Glass Substrates via RF Sputtering

Fabrication of Bi2Te3 and Sb2Te3 Thermoelectric Thin Films using Radio Frequency Magnetron Sputtering Technique

Through various studies on thermoelectric (TE) materials, thin film configuration gives superior advantages over conventional bulk TEs, including adaptability to curved and flexible substrates. Several different thin film deposition methods have been explored, yet magnetron sputtering is still favorable due to its high deposition efficiency and scalability. Therefore, this study aims to fabricate a bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3) thin film via the radio frequency (RF) magnetron sputtering method. The thin films were deposited on soda lime glass substrates at ambient temperature. The substrates were first washed using water and soap, ultrasonically cleaned with methanol, acetone, ethanol, and deionized water for 10 min, dried with nitrogen gas and hot plate, and finally treated under UV ozone for 10 min to remove residues before the coating process. A sputter target of Bi2Te3 and Sb2Te3 with Argon gas was used, and pre-sputtering was done to clean the target&#39;s surface. Then, a few clean substrates were loaded into the sputtering chamber, and the chamber was vacuumed until the pressure reached 2 x 10-5 Torr. The thin films were deposited for 60 min with Argon flow of 4 sccm and RF power at 75 W and 30 W for Bi2Te3 and Sb2Te3, respectively. This method resulted in highly uniform n-type Bi2Te3 and p-type Sb2Te3 thin films.

Author Spotlight: Advancements in High-Performance Thermoelectric Thin Films Through Radio Frequency Magnetron Sputtering

The manuscript describes a protocol for radio frequency magnetron sputtering of Bi2Te3 and Sb2Te3 thermoelectric thin films on glass substrates, which represents a reliable deposition method that provides a wide range of applications with the potential for further development.

Through various studies on thermoelectric (TE) materials, thin film configuration gives superior advantages over conventional bulk TEs, including ...

Production of CdSe&#45;SnSe Nanocomposites from Consolidated SnSe Particles

Solution&#45;Processed, Surface&#45;Engineered, Polycrystalline CdSe&#45;SnSe Exhibiting Low Thermal Conductivity

In recent years, solution processes have gained considerable traction as a cost-effective and scalable method to produce high-performance thermoelectric materials. The process entails a series of critical steps: synthesis, purification, thermal treatments, and consolidation, each playing a pivotal role in determining performance, stability, and reproducibility. We have noticed a need for more comprehensive details for each of the described steps in most published works. Recognizing the significance of detailed synthetic protocols, we describe here the approach used to synthesize and characterize one of the highest-performing polycrystalline p-type SnSe. In particular, we report the synthesis of SnSe particles in water and the subsequent surface treatment with CdSe molecular complexes that yields CdSe-SnSe nanocomposites upon consolidation. Moreover, the surface treatment inhibits grain growth through Zenner pinning of secondary phase CdSe nanoparticles and enhances defect formation at different length scales. The enhanced complexity in the CdSe-SnSe nanocomposite microstructure with respect to SnSe promotes phonon scattering and thereby significantly reduces the thermal conductivity. Such surface engineering provides opportunities in solution processing for introducing and controlling defects, making it possible to optimize the transport properties and attain a high thermoelectric figure of merit.

Author Spotlight: Advancing Energy Solutions Using Nanocomposites as Processed Thermoelectric Materials

CdSe-SnSe nanocomposites are produced by consolidating surface-engineered SnSe particles. A simple aqueous synthesis is employed to produce SnSe particles. Coating SnSe particles with CdSe molecular complexes allows for controlling grain size and increasing the number of defects present in the nanocomposite, thus lowering the thermal conductivity.

In recent years, solution processes have gained considerable traction as a cost-effective and scalable method to produce high-performance thermoelectric ...

Synthesis of High-ZT Thermoelectric Materials via Mechanochemical Methods

Demonstrating the Simplicity and In Situ Temperature Monitoring of the Mechanochemical Synthesis of Metal Chalcogenides Suitable for Thermoelectrics

Mechanochemical synthesis is an extremely useful strategy to reach thermoelectric materials due to its solvent-free one-step character, as the targeted thermoelectricity (TE) materials in a nanocrystalline format can be prepared by mere high-energy milling of elemental precursors. Nevertheless, the subsequent densification method (e.g., spark plasma sintering or hot pressing) is required afterward, similarly to other synthetic methodologies. In this study, the simplicity of mechanochemical synthesis is&#160;presented for two selected metal chalcogenides, namely copper sulfide (Cu1.8S, digenite) and tin selenide (SnSe, svetlanaite), which are known for high ZT values. These compounds can be prepared via a mechanically induced self-propagating reaction (MSR), which is a combustion-like process instantly yielding the products in a very short timeframe (within 1 min). The occurrence of MSR can be well-tracked by in situ temperature monitoring since an abrupt temperature increase occurs at the moment of MSR. We have developed a device which is capable of monitoring the temperature inside the milling jar every 80 ms during planetary ball milling, and it is therefore possible to very precisely track the moment of MSR ignition. The developed device presents an improvement in the monitoring capabilities in comparison with commercially available analogs. This contribution aims to provide a visual insight into all steps, with simple high-energy ball milling of elements to reach TE materials and in situ temperature monitoring being the central points.

Here, we present a protocol to synthesize two metal chalcogenides (Cu1.8S and SnSe) suitable for thermoelectrics via an ultrafast (second-range), solvent-free, and one-step mechanochemical synthesis using elemental precursors. Simultaneously, we demonstrate the monitoring of the temperature in the jar during planetary ball milling in situ by the newly developed device.

Mechanochemical synthesis is an extremely useful strategy to reach thermoelectric materials due to its solvent-free one-step character, as the targeted ...

Asymmetric Thermoelectrochemical Cell for Harvesting Low-grade Heat under Isothermal Operation

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