# Flexible Active Peltier Coolers Based on Interconnected Magnetic Nanowire Networks

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Results and Discussion

## 3. Conclusions

## 4. Experimental Section

#### 4.1. Fabrication of Flexible Nanowire-Based TE Devices

#### 4.2. Electrical and Thermoelectric Measurements

## Supplementary Materials

## Author Contributions

## Funding

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## References

- Fan, Z.; Zhang, Y.; Pan, L.; Ouyang, J.; Zhang, Q. Recent developments in flexible thermoelectrics: From materials to devices. Renew. Sustain. Energy Rev.
**2021**, 137, 110448. [Google Scholar] [CrossRef] - Zhang, L.; Shi, X.L.; Yang, Y.L.; Chen, Z.G. Flexible thermoelectric materials and devices: From materials to applications. Mater. Today
**2021**, 46, 62–108. [Google Scholar] [CrossRef] - Wang, Y.; Yang, L.; Shi, X.L.; Shi, X.; Chen, L.; Dargusch, M.S.; Zou, J.; Chen, Z.G. Flexible Thermoelectric Materials and Generators: Challenges and Innovations. Adv. Mater.
**2019**, 31, 1807916. [Google Scholar] [CrossRef] [PubMed] - Cao, T.; Shi, X.L.; Chen, Z.G. Advances in the design and assembly of flexible thermoelectric device. Prog. Mater. Sci.
**2023**, 131, 101003. [Google Scholar] [CrossRef] - Bahk, J.H.; Fang, H.; Yazawa, K.; Shakouri, A. Flexible thermoelectric materials and device optimization for wearable energy harvesting. J. Mater. Chem. C
**2015**, 3, 10362–10374. [Google Scholar] [CrossRef] - Du, Y.; Xu, J.; Paul, B.; Eklund, P. Flexible thermoelectric materials and devices. Appl. Mater. Today
**2018**, 12, 366–388. [Google Scholar] [CrossRef] - Lin, S.; Zhang, L.; Zeng, W.; Shi, D.; Liu, S.; Ding, X.; Yang, B.; Liu, J.; Lam, K.h.; Huang, B.; et al. Flexible thermoelectric generator with high Seebeck coefficients made from polymer composites and heat-sink fabrics. Commun. Mater.
**2022**, 3, 44. [Google Scholar] [CrossRef] - Masoumi, S.; O’Shaughnessy, S.; Pakdel, A. Organic-based flexible thermoelectric generators: From materials to devices. Nano Energy
**2022**, 92, 106774. [Google Scholar] [CrossRef] - Li, Y.; Lou, Q.; Yang, J.; Cai, K.; Liu, Y.; Lu, Y.; Qiu, Y.; Lu, Y.; Wang, Z.; Wu, M.; et al. Exceptionally High Power Factor Ag2Se/Se/Polypyrrole Composite Films for Flexible Thermoelectric Generators. Adv. Funct. Mater.
**2022**, 32, 2106902. [Google Scholar] [CrossRef] - Scholdt, M.; Do, H.; Lang, J.; Gall, A.; Colsmann, A.; Lemmer, U.; Koenig, J.D.; Winkler, M.; Boettner, H. Organic Semiconductors for Thermoelectric Applications. J. Electron. Mater.
**2010**, 39, 1589–1592. [Google Scholar] [CrossRef] - Kim, G.H.; Shao, L.; Zhang, K.; Pipe, K.P. Engineered doping of organic semiconductors for enhanced thermoelectric efficiency. Nat. Mater.
**2013**, 12, 719–723. [Google Scholar] [CrossRef] [PubMed] - Bubnova, O.; Khan, Z.U.; Malti, A.; Braun, S.; Fahlman, M.; Berggren, M.; Crispin, X. Optimization of the thermoelectric figure of merit in the conducting polymer poly(3,4-ethylenedioxythiophene). Nat. Mater.
**2011**, 10, 429–433. [Google Scholar] [CrossRef] [PubMed] - Bubnova, O.; Crispin, X. Towards polymer-based organic thermoelectric generators. Energy Environ. Sci.
**2012**, 5, 9345–9362. [Google Scholar] [CrossRef] - Yakuphanoglu, F.; Şenkal, B.F.; Saraç, A. Electrical Conductivity, Thermoelectric Power, and Optical Properties of Organo-Soluble Polyaniline Organic Semiconductor. J. Electron. Mater.
**2008**, 37, 930–934. [Google Scholar] [CrossRef] - Tang, X.; Liu, T.; Li, H.; Yang, D.; Chen, L.; Tang, X. Notably enhanced thermoelectric properties of lamellar polypyrrole by doping with β-naphthalene sulfonic acid. RSC Adv.
**2017**, 7, 20192–20200. [Google Scholar] [CrossRef] - Du, Y.; Shen, S.Z.; Cai, K.; Casey, P.S. Research progress on polymer–inorganic thermoelectric nanocomposite materials. Prog. Polym. Sci.
**2012**, 37, 820–841. [Google Scholar] [CrossRef] - Yao, Q.; Chen, L.; Zhang, W.; Liufu, S.; Chen, X. Enhanced Thermoelectric Performance of Single-Walled Carbon Nanotubes/Polyaniline Hybrid Nanocomposites. ACS Nano
**2010**, 4, 2445–2451. [Google Scholar] [CrossRef] - Meng, C.; Liu, C.; Fan, S. A Promising Approach to Enhanced Thermoelectric Properties Using Carbon Nanotube Networks. Adv. Mater.
**2010**, 22, 535–539. [Google Scholar] [CrossRef] - Du, Y.; Cai, K.F.; Chen, S.; Cizek, P.; Lin, T. Facile Preparation and Thermoelectric Properties of Bi2Te3 Based Alloy Nanosheet/PEDOT:PSS Composite Films. ACS Appl. Mater. Interfaces
**2014**, 6, 5735–5743. [Google Scholar] [CrossRef] - Wan, C.; Gu, X.; Dang, F.; Itoh, T.; Wang, Y.; Sasaki, H.; Kondo, M.; Koga, K.; Yabuki, K.; Snyder, G.J.; et al. Flexible n-type thermoelectric materials by organic intercalation of layered transition metal dichalcogenide TiS2. Nat. Mater.
**2015**, 14, 622–627. [Google Scholar] [CrossRef] - Tian, R.; Wan, C.; Wang, Y.; Wei, Q.; Ishida, T.; Yamamoto, A.; Tsuruta, A.; Shin, W.; Li, S.; Koumoto, K. A solution-processed TiS
_{2}/organic hybrid superlattice film towards flexible thermoelectric devices. J. Mater. Chem.**2017**, 5, 564–570. [Google Scholar] [CrossRef] - He, R.; Schierning, G.; Nielsch, K. Thermoelectric Devices: A Review of Devices, Architectures, and Contact Optimization. Adv. Mater. Technol.
**2018**, 3, 1700256. [Google Scholar] [CrossRef] - Hong, S.; Gu, Y.; Seo, J.K.; Wang, J.; Liu, P.; Meng, Y.S.; Xu, S.; Chen, R. Wearable thermoelectrics for personalized thermoregulation. Sci. Adv.
**2019**, 5, eaaw0536. [Google Scholar] [CrossRef] [PubMed] - Xu, S.; Li, M.; Dai, Y.; Hong, M.; Sun, Q.; Lyu, W.; Liu, T.; Wang, Y.; Zou, J.; Chen, Z.G.; et al. Realizing a 10 °C Cooling Effect in a Flexible Thermoelectric Cooler Using a Vortex Generator. Adv. Mater.
**2022**, 34, 2204508. [Google Scholar] [CrossRef] [PubMed] - Sivarenjini, T.M.; Panbude, A.; Sathiyamoorthy, S.; Kumar, R.; Maaza, M.; Kaliappan, J.; Veluswamy, P. Design and Optimization of Flexible Thermoelectric Coolers for Wearable Applications. ECS J. Solid State Sci. Technol.
**2021**, 10, 081006. [Google Scholar] [CrossRef] - Dabrowska, A.; Kobus, M.; Starzak, L.; Pekoslawski, B. Analysis of Efficiency of Thermoelectric Personal Cooling System Based on Utility Tests. Materials
**2022**, 15, 1115. [Google Scholar] [CrossRef] [PubMed] - Pop, E.; Sinha, S.; Goodson, K. Heat Generation and Transport in Nanometer-Scale Transistors. Proc. IEEE
**2006**, 94, 1587–1601. [Google Scholar] [CrossRef] - Cai, Y.; Wang, Y.; Liu, D.; Zhao, F.Y. Thermoelectric cooling technology applied in the field of electronic devices: Updated review on the parametric investigations and model developments. Appl. Therm. Eng.
**2019**, 148, 238–255. [Google Scholar] [CrossRef] - Sharp, J.; Bierschenk, J.; Lyon, H. Overview of Solid-State Thermoelectric Refrigerators and Possible Applications to On-Chip Thermal Management. Proc. IEEE
**2006**, 94, 1602–1612. [Google Scholar] [CrossRef] - Adams, M.; Verosky, M.; Zebarjadi, M.; Heremans, J. Active Peltier Coolers Based on Correlated and Magnon-Drag Metals. Phys. Rev. Applied
**2019**, 11, 054008. [Google Scholar] [CrossRef] - Parker, M. Going with the flow (of heat). Nat. Electron.
**2019**, 2, 211. [Google Scholar] [CrossRef] - Mao, J.; Chen, G.; Ren, Z. Thermoelectric cooling materials. Nat. Mater.
**2021**, 20, 454–461. [Google Scholar] [CrossRef] [PubMed] - Zebarjadi, M. Electronic cooling using thermoelectric devices. Appl. Phys. Lett.
**2015**, 106, 203506. [Google Scholar] [CrossRef] - Rowe, D.M.; Kuznetsov, V.L.; Kuznetsova, L.A.; Min, G. Electrical and thermal transport properties of intermediate-valence YbAl3. J. Phys. Appl. Phys.
**2002**, 35, 2183–2186. [Google Scholar] [CrossRef] - Vandaele, K.; Watzman, S.J.; Flebus, B.; Prakash, A.; Zheng, Y.; Boona, S.R.; Heremans, J.P. Thermal spin transport and energy conversion. Mater. Today Phys.
**2017**, 1, 39–49. [Google Scholar] [CrossRef] - Fert, A.; Piraux, L. Magnetic nanowires. J. Magn. Magn. Mater.
**1999**, 200, 338–358. [Google Scholar] [CrossRef] - Staňo, M.; Fruchart, O.; Brück, E. Magnetic Nanowires and Nanotubes. In Handbook of Magnetic Materials; Elsevier: Amsterdam, The Netherlands, 2018; Volume 27, Chapter 3; pp. 155–267. [Google Scholar] [CrossRef]
- He, H.; Tao, N.J. Electrochemical fabrication of metal nanowires. Encycl. Nanosci. Nanotechnol.
**2003**, 2, 755–772. [Google Scholar] - Caballero-Calero, O.; Martín-González, M. Thermoelectric nanowires: A brief prospective. Scr. Mater.
**2016**, 111, 54–57. [Google Scholar] [CrossRef] - Domínguez-Adame, F.; Martín-González, M.; Sánchez, D.; Cantarero, A. Nanowires: A route to efficient thermoelectric devices. Phys. Low-Dimens. Syst. Nanostruct.
**2019**, 113, 213–225. [Google Scholar] [CrossRef] - da Câmara Santa Clara Gomes, T.; Abreu Araujo, F.; Piraux, L. Making flexible spin caloritronic devices with interconnected nanowire networks. Sci. Adv.
**2019**, 5, eaav2782. [Google Scholar] [CrossRef] - Abreu Araujo, F.; da Câmara Santa Clara Gomes, T.; Piraux, L. Magnetic Control of Flexible Thermoelectric Devices Based on Macroscopic 3D Interconnected Nanowire Networks. Adv. Electron. Mater.
**2019**, 5, 1800819. [Google Scholar] [CrossRef] - da Câmara Santa Clara Gomes, T.; Marchal, N.; Abreu Araujo, F.; Piraux, L. Spin Caloritronics in 3D Interconnected Nanowire Networks. Nanomaterials
**2020**, 10, 2092. [Google Scholar] [CrossRef] [PubMed] - Piraux, L.; da Câmara Santa Clara Gomes, T.; Abreu Araujo, F.; De La Torre Medina, J. 3D magnetic nanowire networks. In Magnetic Nano- and Microwires, 2nd ed.; Vázquez, M., Ed.; Elsevier: Amsterdam, The Netherlands, 2020; Chapter 27. [Google Scholar]
- da Câmara Santa Clara Gomes, T.; Marchal, N.; Araujo, F.A.; Piraux, L. Flexible thermoelectric films based on interconnected magnetic nanowire networks. J. Phys. Appl. Phys.
**2022**, 55, 223001. [Google Scholar] [CrossRef] - da Câmara Santa Clara Gomes, T.; Marchal, N.; Abreu Araujo, F.; Piraux, L. Magnetically Activated Flexible Thermoelectric Switches Based on Interconnected Nanowire Networks. Adv. Mater. Technol.
**2022**, 7, 2101043. [Google Scholar] [CrossRef] - Ashcroft, N.W.; Mermin, N.D. Solid State Physics; Holt, Rinehart and Winston: New York, NY, USA, 1976. [Google Scholar]
- Tian, M.; Wang, J.; Kurtz, J.; Mallouk, T.E.; Chan, M.H.W. Electrochemical Growth of Single-Crystal Metal Nanowires via a Two-Dimensional Nucleation and Growth Mechanism. Nano Lett.
**2003**, 3, 919–923. [Google Scholar] [CrossRef] [PubMed] - Durkan, C.; Welland, M.E. Size effects in the electrical resistivity of polycrystalline nanowires. Phys. Rev. B
**2000**, 61, 14215–14218. [Google Scholar] [CrossRef] - Ye, S.; Rathmell, A.R.; Chen, Z.; Stewart, I.E.; Wiley, B.J. Metal Nanowire Networks: The Next Generation of Transparent Conductors. Adv. Mater.
**2014**, 26, 6670–6687. [Google Scholar] [CrossRef] [PubMed] - Yoo, E.; Moon, J.H.; Jeon, Y.S.; Kim, Y.; Ahn, J.P.; Kim, Y.K. Electrical resistivity and microstructural evolution of electrodeposited Co and Co-W nanowires. Mater. Charact.
**2020**, 166, 110451. [Google Scholar] [CrossRef] - Meaden, G.T. Electrical Resistance of Metals; Springer: New York, NY, USA, 1965. [Google Scholar]
- Rowe, D.M. CRC Handbook of Thermoelectrics; CRC Press: Boca Raton, FL, USA, 1995. [Google Scholar]
- Heremans, J.P.; Wiendlocha, B. Tetradymites: Bi2Te3-Related Materials. In Materials Aspect of Thermoelectricity; CRC Press: Boca Raton, FL, USA, 2016; pp. 53–108. [Google Scholar]
- Heikes, R.R.; Ure, R.W. Thermoelectricity: Science and Engineering; Interscience Publishers: New York, NY, USA, 1961. [Google Scholar]
- Zhang, Z.; Chen, J. Thermal conductivity of nanowires. Chin. Phys. B
**2018**, 27, 035101. [Google Scholar] [CrossRef] - Yang, X.; Wang, C.; Lu, R.; Shen, Y.; Zhao, H.; Li, J.; Li, R.; Zhang, L.; Chen, H.; Zhang, T.; et al. Progress in measurement of thermoelectric properties of micro/nano thermoelectric materials: A critical review. Nano Energy
**2022**, 101, 107553. [Google Scholar] [CrossRef] - Lu, R.; Yang, X.; Wang, C.; Shen, Y.; Zhang, T.; Zheng, X.; Chen, H. Integrated measurement of thermoelectric properties for filamentary materials using a modified hot wire method. Rev. Sci. Instruments
**2022**, 93, 125107. [Google Scholar] [CrossRef] - Rojo, M.M.; Calero, O.C.; Lopeandia, A.F.; Rodriguez-Viejo, J.; Martín-Gonzalez, M. Review on measurement techniques of transport properties of nanowires. Nanoscale
**2013**, 5, 11526–11544. [Google Scholar] [CrossRef] [PubMed] - Ou, M.N.; Yang, T.J.; Harutyunyan, S.R.; Chen, Y.Y.; Chen, C.D.; Lai, S.J. Electrical and thermal transport in single nickel nanowire. Appl. Phys. Lett.
**2008**, 92, 063101. [Google Scholar] [CrossRef] - Kojda, D.; Mitdank, R.; Handwerg, M.; Mogilatenko, A.; Albrecht, M.; Wang, Z.; Ruhhammer, J.; Kroener, M.; Woias, P.; Fischer, S.F. Temperature-dependent thermoelectric properties of individual silver nanowires. Phys. Rev. B
**2015**, 91, 024302. [Google Scholar] [CrossRef] - Wang, J.; Wu, Z.; Mao, C.; Zhao, Y.; Yang, J.; Chen, Y. Effect of Electrical Contact Resistance on Measurement of Thermal Conductivity and Wiedemann-Franz Law for Individual Metallic Nanowires. Sci. Rep.
**2018**, 8, 4862. [Google Scholar] [CrossRef] - Petsagkourakis, I.; Tybrandt, K.; Crispin, X.; Ohkubo, I.; Satoh, N.; Mori, T. Thermoelectric materials and applications for energy harvesting power generation. Sci. Technol. Adv. Mater.
**2018**, 19, 836–862. [Google Scholar] [CrossRef] [PubMed] - Macia, E. Thermoelectric Materials: Advances and Applications; CRC Press: Boca Raton, FL, USA, 2015. [Google Scholar]
- Yamashita, O.; Tomiyoshi, S.; Makita, K. Bismuth telluride compounds with high thermoelectric figures of merit. J. Appl. Phys.
**2002**, 93, 368–374. [Google Scholar] [CrossRef] - Heremans, J.P.; Cava, R.J.; Samarth, N. Tetradymites as thermoelectrics and topological insulators. Nat. Rev. Mater.
**2017**, 2, 17049. [Google Scholar] [CrossRef] - Chung, D.Y.; Hogan, T.; Brazis, P.; Rocci-Lane, M.; Kannewurf, C.; Bastea, M.; Uher, C.; Kanatzidis, M.G. CsBi
_{4}Te_{6}: A High-Performance Thermoelectric Material for Low-Temperature Applications. Science**2000**, 287, 1024–1027. [Google Scholar] [CrossRef] - Mao, J.; Zhu, H.; Ding, Z.; Liu, Z.; Gamage, G.A.; Chen, G.; Ren, Z. High thermoelectric cooling performance of n-type Mg
_{3}B_{2}-based materials. Science**2019**, 365, 495–498. [Google Scholar] [CrossRef] - Pan, Y.; Yao, M.; Hong, X.; Zhu, Y.; Fan, F.; Imasato, K.; He, Y.; Hess, C.; Fink, J.; Yang, J.; et al. Mg
_{3}(Bi,Sb)_{2}single crystals towards high thermoelectric performance. Energy Environ. Sci.**2020**, 13, 1717–1724. [Google Scholar] [CrossRef] - Sun, P.; Ikeno, T.; Mizushima, T.; Isikawa, Y. Simultaneously optimizing the interdependent thermoelectric parameters in Ce(
_{Ni1-x}Cu_{x})_{2}Al_{3}. Phys. Rev. B**2009**, 80, 193105. [Google Scholar] [CrossRef] - Boona, S.R.; Morelli, D.T. Enhanced thermoelectric properties of CePd
_{3-x}Pt_{x}. Appl. Phys. Lett.**2012**, 101, 101909. [Google Scholar] [CrossRef] - Issi, J.P. Low Temperature Transport Properties of the Group V Semimetals. Aust. J. Phys.
**1979**, 32, 585–628. [Google Scholar] [CrossRef] - Blatt, F.J. Magnetic Field Dependence of the Thermoelectric Power of Iron. Can. J. Phys.
**1972**, 50, 2836–2839. [Google Scholar] [CrossRef] - Arajs, S.; Anderson, E.E.; Ebert, E.E. Absolute thermoelectric power of chromium-silicon alloys. Il Nuovo C. B 1971–1996
**1971**, 4, 40–50. [Google Scholar] [CrossRef] - Ho, C.Y.; Bogaard, R.H.; Chi, T.C.; Havill, T.N.; James, H.M. Thermoelectric power of selected metals and binary alloy systems. Thermochimica Acta
**1993**, 218, 29–56. [Google Scholar] [CrossRef] - Wehmeyer, G.; Yabuki, T.; Monachon, C.; Wu, J.; Dames, C. Thermal diodes, regulators, and switches: Physical mechanisms and potential applications. Appl. Phys. Rev.
**2017**, 4, 041304. [Google Scholar] [CrossRef] - Klinar, K.; Kitanovski, A. Thermal control elements for caloric energy conversion. Renew. Sustain. Energy Rev.
**2020**, 118, 109571. [Google Scholar] [CrossRef] - da Câmara Santa Clara Gomes, T.; de la Torre Medina, J.; Velázquez-Galván, Y.G.; Martínez-Huerta, J.M.; Encinas, A.; Piraux, L. Interplay between the magnetic and magneto-transport properties of 3D interconnected nanowire networks. J. Appl. Phys.
**2016**, 120, 043904. [Google Scholar] [CrossRef] - da Câmara Santa Clara Gomes, T.; De La Torre Medina, J.; Lemaitre, M.; Piraux, L. Magnetic and Magnetoresistive Properties of 3D Interconnected NiCo Nanowire Networks. Nanoscale Res. Lett.
**2016**, 11, 466. [Google Scholar] [CrossRef] [PubMed] - Ferain, E.; Legras, R. Track-etch templates designed for micro- and nanofabrication. Nucl. Instrum. Methods Phys. Res. Sect. Beam Interact. Mater. Atoms
**2003**, 208, 115–122. [Google Scholar] [CrossRef] - Kamalakar, M.V.; Raychaudhuri, A.K. Low temperature electrical transport in ferromagnetic Ni nanowires. Phys. Rev. B
**2009**, 79, 205417. [Google Scholar] [CrossRef] - Marchal, N.; da Câmara Santa Clara Gomes, T.; Abreu Araujo, F.; Piraux, L. Large spin-dependent thermoelectric effects in NiFe-based interconnected nanowire networks. Nanoscale Res. Lett.
**2020**, 15, 137. [Google Scholar] [CrossRef] [PubMed] - Laubitz, M.J.; Matsumura, T. Transport properties of the ferromagnetic metals. I. Cobalt. Can. J. Phys.
**1973**, 51, 1247–1256. [Google Scholar] [CrossRef]

**Figure 1.**Flexible thermoelectric coolers based on interconnected nanowire networks. (

**a**,

**b**) Fabrication technique of a thermoelectric device consisting of p- and n-type interconnected metallic nanowire networks (with Fe for p-type and Co for n-type materials). The Co and Fe NW networks, shown in orange and green respectively, are obtained via direct electrodeposition from a Au cathode within a three-dimensional porous polycarbonate membrane (

**a**). The thermocouple is made after local removal of the Au electrode via plasma etching (

**b**). The temperature at the thermoelectric junction can be raised by means of a resistive heater. Cernox resistance thermometers are used to determine the temperatures of the cold and hot junctions. The inset in (

**b**) shows the current path in the nanowire networks. (

**c**) Picture of the nanowire-based active cooler corresponding to the schematics in (

**b**), showing the flexible and self-supported device. (

**d**,

**e**) Scanning electron microscopy images of self-supported interconnected Co nanowires with 105 nm diameter showing a 50°-tilted view of the macroscopic nanowire network film (

**d**) and the nanowire branched structure at higher magnification (

**e**).

**Figure 2.**Comparison of the active cooling performance among several flexible thermoelectric materials. (

**a**) Thermoelectric power factor PF vs. thermal conductivity $\kappa $ for flexible TE systems made of n-type (red symbols) and p-type (green symbols) magnetic nanowire networks [45], conductive polymers, organic/inorganic hybrids and continuous inorganic films [1,2,3]. The data for conventional bulk thermoelectric materials near room temperature [64,65,66,67,68,69], correlated metals [34,70,71], group V semimetals [72] and transition metals and alloys [30,35,52,53,73,74,75] are also presented. The gray dashed line shows the case $ZT=1$ (with $Z=$ PF/$\kappa $ as the figure of merit), which corresponds to the best power conversion efficiency achievable to date. The most suitable active Peltier coolers are located at the top right of the graph, as indicated by the red arrow. In contrast, the most suitable materials for conventional Peltier refrigeration are located at the bottom right of the graph, as indicated by the gray arrow. (

**b**,

**c**) Schematic drawings showing the differences between active cooling (

**b**) and refrigeration (

**c**). In the active cooling mode, Peltier heat flows from the hot side to the cold side, increasing Fourier heat conduction rather than opposing it as in the refrigeration mode.

**Figure 3.**Device characterization as a function of current injection. (

**a**,

**b**) Measured total temperature changes at the Peltier junction of the NW-based thermocouple versus current intensity applied both forward and reverse for samples 1 (

**a**) and 2 (

**b**), respectively. The dotted lines provide a fit, including Joule and Peltier contributions to temperature variations. The insets in (

**a**,

**b**) show schematics of the hot side of thermoelectric coolers consisting of networks of interconnected Co and Fe nanowires of 105 nm in diameter partially filling a porous polymer film (

**a**), with the same nanowire constituents completely filling the porous medium with the formation of a thin metallic layer on the surface in (

**b**). (

**c**,

**d**) Temperature versus time traces of the sum of the Joule and Peltier heats relative to a working temperature of 300 K, as recorded using the Cernox sensor. The direct currents of 420 mA for sample 1 (

**c**) and of 590 mA for sample 2 (

**d**) are applied sequentially forward and reverse in the NW-based thermocouple. Error bars in (

**a**,

**b**) are smaller than the markers, reflecting the uncertainty of the voltage and temperature measurements, and they are set to two times the standard deviation, gathering 95% of the data variation (See Supporting Information Section S3 for details).

**Figure 4.**Active cooling of an electronic device. (

**a**,

**b**) Temperature variations of the Cernox sensor as a function of thermal load when optimal electric currents and zero current are passed through the partially filled (

**a**) and completely filled (

**b**) Co and Fe nanowire thermocouples. The slopes of the lines provide the thermal conductance. Insets: $\Delta T$ vs. Q plots on log-log scales. (

**c**) The time dependence of temperature changes during successive switching on of the thermal load on the thermoelectric junction and the optimal cooling current of samples 1 (in black, $Q=$ 0.5 mW and ${I}_{\mathrm{opt}}=$−420 mA) and 2 (in yellow, $Q=$ 1.2 mW and ${I}_{\mathrm{opt}}=$−590 mA). (

**d**) Variation in effective thermal conductance ${K}_{\mathrm{eff}}$ normalized by the passive-mode thermal conductance K with the temperature gradient $\Delta T$ for partially filled and completely filled Co and Fe nanowire thermocouples at the optimal switching currents. Error bars in (

**a**,

**b**,

**d**) reflect the uncertainty of the voltage and temperature measurements, and they are set to two times the standard deviation, gathering 95% of the data variation (See Supporting Information Section S3 for details).

Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content. |

© 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

## Share and Cite

**MDPI and ACS Style**

da Câmara Santa Clara Gomes, T.; Marchal, N.; Abreu Araujo, F.; Piraux, L.
Flexible Active Peltier Coolers Based on Interconnected Magnetic Nanowire Networks. *Nanomaterials* **2023**, *13*, 1735.
https://doi.org/10.3390/nano13111735

**AMA Style**

da Câmara Santa Clara Gomes T, Marchal N, Abreu Araujo F, Piraux L.
Flexible Active Peltier Coolers Based on Interconnected Magnetic Nanowire Networks. *Nanomaterials*. 2023; 13(11):1735.
https://doi.org/10.3390/nano13111735

**Chicago/Turabian Style**

da Câmara Santa Clara Gomes, Tristan, Nicolas Marchal, Flavio Abreu Araujo, and Luc Piraux.
2023. "Flexible Active Peltier Coolers Based on Interconnected Magnetic Nanowire Networks" *Nanomaterials* 13, no. 11: 1735.
https://doi.org/10.3390/nano13111735