In-situ and ex-situ measurements of thermal conductivity of supercapacitors

AbstractThermal signature of supercapacitors are investigated in-situ and ex-situ using commercial supercapacitors.Regarding the in-situ method, four supercapacitors were connected in series, with thermocouples embedded between the supercapacitors. As the applied current was increased, the temperature measured at the intrinsic positions also increased. When cycling at a current density of 0.11 A cm−2 the centre temperature increased by 14 K compared to the stack surface temperature. This is an important figure as literature states that an increase of 10 K leads to a corresponding decrease in the lifetime by a factor of 2. Using the obtained temperature profiles, the effective thermal conductivity of the stack was found to vary between 0.5 W K−1 m−1 and 1.0 W K−1 m−1, depending on the compaction of the stack.For the ex-situ measurements, the thermal conductivity and the thicknesses of the supercapacitor material layers were measured individually in order to determine the corresponding thermal conductivity of the stack. When using this method an effective thermal conductivity of the stack of 0.53 ± 0.06 W K−1 m−1 was obtained. The analysis also demonstrated that the main contributor to the thermal resistivity and conductivity of the supercapacitor construction is the electrodes. This demonstrates that when managing heat from supercapacitors it is important to focus on the thermal conductivity of the components materials

Ring current effects: Factors affecting the NMR chemical shift of molecules adsorbed on porous carbons

Nuclear magnetic resonance (NMR) spectroscopy is increasingly being used to study the adsorption of molecules in porous carbons, a process which underpins applications ranging from electrochemical energy storage to water purification. Here we present density functional theory (DFT) calculations of the nucleus-independent chemical shift (NICS) near various sp2-hybridized carbon fragments to explore the structural factors that may affect the resonance frequencies observed for adsorbed species. The domain size of the delocalized electron system affects the calculated NICSs, with larger domains giving rise to larger chemical shieldings. In slit pores, overlap of the ring current effects from the pore walls is shown to increase the chemical shielding. Finally, curvature in the carbon sheets is shown to have a significant effect on the NICS. The trends observed are consistent with existing NMR results as well as new spectra presented for an electrolyte adsorbed on carbide-derived carbons prepared at different temperatures.A.C.F., J.M.G., and C.P.G. acknowledge the Sims Scholarship (A.C.F.), EPSRC (via the Supergen consortium; J.M.G.), and the EU ERC (via an Advanced Fellowship to C.P.G.) for funding. CDC synthesis at Drexel University was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award #ER46473. V.P. acknowledges funding from the German Federal Ministry for Research and Education (BMBF) in support of the nanoEES3D project (Award 03EK3013) as part of the strategic funding initiative energy storage framework and thanks Prof. Eduard Arzt (INM) for his continuing support. Mohamed Shamma and Boris Dyatkin (Drexel University) are thanked for their support in the synthesis of CDC material. DFT calculations were performed using the Darwin Supercomputer of the University of Cambridge High Performance Computing Service, provided by Dell Inc. using Strategic Research Infrastructure Funding from the Higher Education Funding Council for England and funding from the Science and Technology Facilities Council.This is the author accepted manuscript. The final version is available from the American Chemical Society via http://dx.doi.org/10.1021/jp502387

Author Correction: Salt concentration and charging velocity determine ion charge storage mechanism in nanoporous supercapacitors

Correction to: Nature Communications; https://doi.org/10.1038/s41467-018-06612-4; published online 08 October 2018 The original version of this Article contained an error in the Acknowledgements, which was incorrectly omitted from the end of the following: ‘The research leading to these results has received funding from the European Community’s Horizon 2020 Framework Programme under grant agreement nº 730872.’ This has been corrected in both the PDF and HTML versions of the Article

Referendum Design and Contingent Valuation: The NOAA Panel's No-Vote Recommendation

In 1992 the National Oceanic and Atmospheric Administration (NOAA) convened a panel of prominent social scientists to assess the reliability of natural resource damage estimates derived from contingent valuation (CV). The product of the Panel's deliberations was a report that laid out a set of recommended guidelines for CV survey design, administration, and data analysis. One of the Panel's recommendations was that CV surveys should employ a referendum approach. This method describes a choice mechanism that asks each respondent how they would vote if faced with a particular program and the prospect of paying for the program through some means, such as higher taxes. The Panel also recommended that CV referendum questions which commonly use only "for" or "against" answers should be expanded to explicitly offer an "I would-not-vote" response. The purpose of this paper is to consider the effects of such a "would-not-vote" option. In developing the test, we followed the important elements of the NOAA Panel guidelines for the design and administration of a CV survey and use what was acknowledged(by the Panel) as the most carefully developed CV questionnaire to that time, that is, the State of Alaska's study of the Exxon Valdez oil spill. Our findings suggest that when those selecting the "would-not-vote" response are treated as having voted "against" the offered program, offering the option does not alter: (a) the distribution of "for" and "against" responses, (b) the estimates of WTP derived from these choices, or (c) the construct validity of the results.

Temporal Reliability of Estimates from Contingent Valuation

In 1992 the National Oceanic and Atmospheric Administration (NOAA) convened a panel of prominent social scientists to assess the reliability of natural resource damage estimates derived from contingent valuation (CV). The product of the panel's deliberations was a report that laid out a set of recommended guidelines for CV survey design, administration, and data analysis. This paper focuses on one of these guidelines�the Panel's call for the "temporal averaging" of willingness-to-pay (WTP) responses obtained from CV surveys as one method for increasing their reliability. The panel suggested: "Time dependent measurement noise should be reduced by averaging across independently drawn samples taken at different points in time. A clear and substantial time trend in the responses would cast doubt on the 'reliability' of the finding." The purpose of this paper is to examine the temporal reliability of CV estimates. Our findings, using a CV instrument designed to measure willingness-to-pay for a program to protect Prince William Sound, Alaska from future oil spills, like the Exxon Valdez spill, exhibited no significant sensitivity to the timing of the interviews. For two samples involving independent interviews taken over two years apart, the distribution of respondents' choices "for" and "against" the protection program did not differ.

Redox-electrolytes for non-flow electrochemical energy storage: A critical review and best practice

Over recent decades, a new type of electric energy storage system has emerged with the principle that the electric charge can be stored not only at the interface between the electrode and the electrolyte but also in the bulk electrolyte by redox activities of the electrolyte itself. Those redox electrolytes are promising for non-flow hybrid energy storage systems, or redox electrolyte-aided hybrid energy storage (REHES) systems; particularly, when they are combined with highly porous carbon electrodes. In this review paper, critical design considerations for the REHES systems are discussed as well as the effective electrochemical characterization techniques. Appropriate evaluation of the electrochemical performance is discussed thoroughly, including advanced analytical techniques for the determination of the electrochemical stability of the redox electrolytes and self-discharge rate. Additionally, critical summary tables for the recent progress on REHES systems are provided. Furthermore, the unique synergistic combination of porous carbon materials and redox electrolytes is introduced in terms of the diffusion, adsorption, and electrochemical kinetics modulating energy storage in REHES systems. © 2018 The Author(s

Emerging, hydrogen-driven electrochemical water purification

Energy-efficient technologies for the remediation of water and generation of drinking water is a key towards sustainable technologies. Electrochemical desalination technologies are promising alternatives towards established methods, such as reverse osmosis or nanofiltration. In the last few years, hydrogen-driven electrochemical water purification has emerged. This review article explores the concept of desalination fuel cells and capacitive-Faradaic fuel cells for ion separation

Was the NOAA Panel Correct About Contingent Valuation?

The past few years have seen a highly charged debate about whether contingent valuation (CV) surveys can provide valid economic measures of people's values for environmental resources. In an effort to appraise the validity of CV measures of economic value, a distinguished panel of social scientists, chaired by two Nobel laureates, was established by NOAA, to critically evaluate the validity of CV measures of nonuse value. The Panel provided an extensive set of guidelines for CV survey construction, administration, and analysis, and distinguished a subset of items from their guidelines for special emphasis and described them as burden of proof requirements. Of particular interest was the Panel's requirement that CV surveys demonstrate "responsiveness to the scope of the environmental insult." That demonstration has come to be called a scope test. The paper reports the findings from the first CV study that adheres to the NOAA Panel's guidelines and includes a formal scope test.

Nanoporous Block Copolymer Membranes with Enhanced Solvent Resistance Via UV-Mediated Cross-Linking Strategies

In this work, a block copolymer (BCP) consisting of poly((butyl methacrylate-co-benzophenone methacrylate-co-methyl methacrylate)-block-(2-hydroxyethyl methacrylate)) (P(BMA-co-BPMA-co-MMA)-b-P(HEMA)) is prepared by a two-step atom-transfer radical polymerization (ATRP) procedure. BCP membranes are fabricated applying the self-assembly and nonsolvent induced phase separation (SNIPS) process from a ternary solvent mixture of tetrahydrofuran (THF), 1,4-dioxane, and dimethylformamide (DMF). The presence of a porous top layer of the integral asymmetric membrane featuring pores of about 30 nm is confirmed via scanning electron microscopy (SEM). UV-mediated cross-linking protocols for the nanoporous membrane are adjusted to maintain the open and isoporous top layer. The swelling capability of the noncross-linked and cross-linked BCP membranes is investigated in water, water/ethanol mixture (1:1), and pure ethanol using atomic force microscopy, proving a stabilizing effect of the UV cross-linking on the porous structures. Finally, the influence of the herein described cross-linking protocols on water-flux measurements for the obtained membranes is explored. As a result, an increased swelling resistance for all tested solvents is found, leading to an increased water flux compared to the pristine membrane. The herein established UV-mediated cross-linking protocol is expected to pave the way to a new generation of porous and stabilized membranes within the fields of separation technologies