Nickel ethenetetrathiolate (NiETT) coordination polymers are shown to exhibit high thermoelectric performance as pressed pellets. Because the material is insoluble, films are formed by fabricating a ...composite of the material in an inert polymer matrix, a process that adversely impacts thermoelectric properties. To date, a reliable and reproducible synthesis has not been reported, which was the motivation for a systematic study of the substeps involved to understand the reaction mechanism. The results of these studies yield optimized reaction conditions for high performance n‐type films, which are derived from empirical studies and material characterization. Herein, a reaction procedure is presented that gives reproducible properties when preparing batches in the 0.5–15 g range. The identity of the counterion, nickel equivalency, and oxidation extent are investigated, which provide insight into the synthetic reaction mechanism and the ligand‐centered oxidation process in these polymers. Optimized materials based on NaNiETT exhibit one of the highest n‐type thermoelectric performance for solution‐processed films reported to date, with power factors of 23 µW (m K)−2 (due to conductivities approaching 50 S cm−1) while maintaining their stability in ambient conditions.
A procedure for the synthesis of an n‐type thermoelectric coordination polymer, Nickel ethenetetrathiolate (NiETT) is reported to give reliable and scalable materials while eliminating batch‐to‐batch variation. A deeper understanding of these insoluble conducting polymers is achieved by systematic synthetic variations and in‐depth materials characterization. This work enables air stable NiETT thin‐film composites with high power factors for thermoelectric harvesting applications.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Development of alternative refrigeration technologies that are efficient and have zero global warming potential is a promising pathway to reduce the effect of the rising global cooling demand on ...climate change. We use lessons from flow batteries and thermally regenerative electrochemical cycles to introduce an electrochemical refrigeration technology based on the Brayton cycle: Brayton electrochemical refrigeration (BECR). Although the proof of concept is demonstrated elsewhere, here we report an analytical framework that elucidates the key parameters involved in BECR and how it may be elevated on the technology readiness scale. We first analyze the ideal BECR cycle to demonstrate the technology’s performance (cooling load and coefficient of performance) in the reversible limit, identify two main practical considerations, and then analyze the non-ideal BECR cycle to simulate realistic performance. Whenever possible, we introduce dimensionless figures of merit to help streamline future concerted research efforts that seek to improve the state of the art.
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•Brayton electrochemical refrigeration (BECR) uses electrochemical entropic heat to cool•Ideal and non-ideal BECR cycles are analyzed to explore cooling capacity and efficiency•Key figures of merit guide future materials and architecture development•Practical limitations bind the technology application space
Novel refrigeration schemes can alleviate global warming caused by modern-day refrigerants used in vapor compression technologies. Rajan and Yee conceptualize an electrochemical refrigerator based on the Brayton cycle. They analyze its performance under ideal and realistic conditions, identify practical limitations, and provide figures of merit to guide future research.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Integrating thermoelectric generators (TEGs) into textiles is attractive for body heat harvesting to power wearable electronics. Textile‐integrated TEGs have the advantage of conformity to the body ...that ensures efficient heat transfer and does not impede movement. Additive printing techniques and solution processable polymer‐based thermoelectric (TE) materials can be used for this purpose. However, a number of fabrication challenges limit the realization of a printed polymer‐based textile TEG using a low cost, scalable, and textile compatible process. In this work, stencil and transfer printing techniques are successfully employed to fabricate a 32‐leg device with a modest fill factor (≈30%) on a commercial sports fabric substrate. PEDOT:PSS and PolyNa(NiETT) are formulated into inks and used as the p‐type and the n‐type polymer materials, respectively. The textile‐integrated TE device yields an open circuit voltage of ≈3 mV at ΔT = 3 K. The fabrication process is scaled up to demonstrate an 864‐leg device that yields a voltage output of ≈47 mV. This work is the first demonstration of a textile TEG based on p‐ and n‐type conducting polymers capable of through‐plane body heat harvesting. It serves as a proof‐of‐concept for integrating TE devices into mainstream fabrics and clothing.
A textile‐integrated thermoelectric device is fabricated using low cost, scalable, and textile compatible fabrication techniques. Polymer p‐ and n‐ type materials are stencil printed on a commercial sports fabric. A heat transfer membrane is heat pressed on both sides of the fabric to add metal interconnects. The 32‐leg prototype yields a voltage of ≈3 mV under body heat harvesting conditions.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The internet is an increasingly popular tool in family and child research that is argued to pose new ethical challenges, yet few studies have systematically assessed the ethical issues of engaging ...parents and children in research online. This scoping review aims to identify and integrate evidence on the ethical issues reported when recruiting, retaining and tracing families and children in research online, and to identify ethical guidelines for internet research.
Academic literature was searched using electronic academic databases (Scopus, PsycINFO, Embase, ERIC, CINAHL and Informit) and handsearching reference lists for articles published in English between January 2006 and February 2016. Grey literature was searched using Google to identify relevant ethical guidelines.
Sixty-five academic articles were included after screening 3,537 titles and abstracts and 205 full-text articles. Most articles reported using the internet to recruit participants (88%) with few reporting online retention (12%) or tracing (10%). Forty percent commented on ethical issues; the majority did not discuss ethics beyond general consent or approval procedures. Some ethical concerns were specific to engaging minors online, including parental consent, age verification and children's vulnerability. Other concerns applied when engaging any research participant online, including privacy and confidentiality, informed consent and disparities in internet access. Five professional guidelines and 10 university guidelines on internet research ethics were identified. Few academic articles (5%) reported using these guidelines.
Engaging families and children in research online introduces unique challenges requiring careful consideration. While researchers regarded themselves as responsible for ensuring research is conducted ethically, lack of use of available guidelines and limited academic literature suggests internet research is occurring without suitable guidance. We recommend broad dissemination of ethical guidelines and encourage researchers to report the methodological and ethical issues of using the internet to engage families and children in research.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Nickel ethenetetrathiolate (NiETT) polymers are promising n‐type thermoelectric (TE) materials, but their insolubility requires the use of an inert polymer matrix to form films, which is detrimental ...to the TE performance. In this work, the use of thermal annealing as a post‐treatment process simultaneously enhances the electrical conductivity from 6 ± 2 to 23 ± 3 S cm−1 and thermopower from −28 ± 3 to −74 ± 4 µV K−1 for NiETT/PVDF composite films. Spectroscopic characterization reveals that the underlying mechanism involves removal of residual solvent and volatile impurities (carbonyl sulfide and water) in the NiETT polymer backbone. Additionally, microscopic characterization reveals morphological changes caused by a densification of the film that improves chain packing. These effects result in a 25 × improvement in power factor from 0.5 to 12.5 µW m−1 K−2 for NiETT/PVDF films and provide insight into the composition of these coordination polymers that maintain their stability under ambient conditions.
Annealing as a post‐treatment to the synthesis and processing of nickel ethenetetrathiolate polymers simultaneously improves the electrical conductivity and Seebeck coefficient, thereby enabling a solution processible, air‐stable n‐type polymer for thermoelectric applications. Spectroscopic characterization reveals the underlying mechanisms involving removal of residual solvent and volatile impurities. Microscopic characterization reveals morphological changes improving film densification.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Polymer dielectrics find applications in modern electronic and electrical technologies due to their low density, durability, high dielectric breakdown strength, and design flexibility. However, they ...are not reliable at high temperatures due to their low mechanical integrity and thermal stability. Herein, a self‐assembled dielectric nanocomposite is reported, which integrates 1D polyaramid nanofibers and 2D boron nitride nanosheets through a vacuum‐assisted layer‐by‐layer infiltration process. The resulting nanocomposite exhibits hierarchical stacking between the 2D nanosheets and 1D nanofibers. Specifically, the 2D nanosheets provide a thermally conductive network while the 1D nanofibers provide mechanical flexibility and robustness through entangled nanofiber–nanosheet morphologies. Experiments and density functional theory show that the nanocomposites through thickness heat transfer processes are nearly identical to that of boron nitride due to synergistic stacking of polyaramid units onto boron nitride nanosheets through van der Waals interactions. The nanocomposite sheets outperform conventional dielectric polymers in terms of mechanical properties (about 4–20‐fold increase of stiffness), light weight (density ≈1.01 g cm−3), dielectric stability over a broad range of temperature (25–200 °C) and frequencies (103–106 Hz), good dielectric breakdown strength (≈292 MV m−1), and excellent thermal management capability (about 5–24 times higher thermal conductivity) such as fast heat dissipation.
A thermally conductive dielectric nanocomposite with mechanical flexibility and robustness and temperature stability is developed by integrating 1D polyaramid nanofibers and 2D boron nitride nanosheets for next‐generation electronic device and electric power systems.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Health authorities encouraged the use of digital contact tracing mobile applications (apps) during the COVID-19 pandemic, but the level of adoption was low because apps offered few direct benefits to ...counterbalance risks to personal privacy. Adoption of such apps could improve if they provided benefits to users. NOVID (COVID-19 Radar), a smartphone app, provided users with personalized data on social proximity of COVID-19 cases and exposed contacts. We analyzed uptake of NOVID at the Georgia Institute of Technology (Georgia Tech) during the 2020-2021 academic year. Data included anonymous NOVID users who self-identified with Georgia Tech and their first- and second-degree network contacts. NOVID achieved 13%-30% adoption at Georgia Tech. Because of technical challenges, adoption waned after an initial peak. The largest increases in adoption (from 41 to 3704) followed administrative promotion of NOVID. Adoption increased modestly (from 2512 to 2661) after faculty- and student-led promotion, such as distribution of door hangers and a public seminar. Two-thirds of on-campus NOVID users were connected to a large network of other users, enabling them to receive data on social proximity of COVID-19 cases and exposed contacts. Network cohesion was observed to emerge rapidly when adoption rates passed just 10%, consistent with estimates from network theory. The key lesson learned in this case study is that top-down administrative promotion outperforms bottom-up grassroots promotion. Relatively high levels of adoption and network cohesion, despite technical challenges during the Georgia Tech pilot of NOVID, illustrate the promise of digital contact tracing when apps provide privacy and inherently beneficial personalized data to their users, especially in regions where Google Apple Exposure Notification is not available.
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NUK, OILJ, SAZU, UKNU, UL, UM, UPUK, VSZLJ
Modeling radiative recombination is crucial to the analysis of radiative energy converters. In this work, a local radiative recombination coefficient is defined and derived based on fluctuational ...electrodynamics that is applicable to thin-film cells in both the near field and far field. The predicted radiative recombination coefficient of an InAs cell deviates from the van Roosbroeck–Shockley relation when the thickness is less than 10 µm, and the difference exceeds fourfold with a 10 nm film. The local radiative recombination coefficient is orders of magnitude higher when an InAs cell is configured in the near field. The local radiative recombination coefficient reduces as the doping level approaches that of a degenerate semiconductor. The maximum output power and efficiency of a thermoradiative cell would be apparently overpredicted if the electroluminescence coefficient defined in this paper were taken as unity for heavily doped semiconductors.
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