Optimization of the electrochemical impedance spectroscopy measurement parameters for PEM fuel cell spectrum determination

Currently, electrochemical Impedance Spectroscopy (EIS) is a widely used tool for the study of electrochemical systems, in general; and fuel cells, in particular. A great effort is typically invested in the analysis of the obtained spectra; whereas, little time is usually spent optimizing the measurement parameters used to obtain these spectra. In general, the default settings provided by the control software used to perform the measurements, or the parameters used in similar systems available in literature, are selected to carry out the measurements. The goal of this work is to determine the optimal measurement parameters for obtaining impedance spectra of a commercial PEM fuel cell. In order to achieve this, a 2^5 factorial design was considered. Five factors were considered, the five impedance spectroscopy measurement parameters: maximum integration time; minimum number of integration cycles; number of stabilization cycles; maximum stabilization time; and minimum cycle fraction. For each factor combination envisaged in the experimental design, the cell spectrum was obtained in given operation conditions, for which the reference spectrum of the system was known, since it had been determined in previous works. The experimentally obtained spectra were fitted to the reference electric equivalent circuit. The mean square error between the experimental data fitting and the reference spectrum fitting was determined in each case, and was used as the dependant variable for the experimental design analysis. An analysis of the variance was performed in order to determine which measurement parameters have a significant effect on the dependant variable; and a model relating the dependant variable and the measurement parameters was built. This model was used in order to obtain the optimal value of each one of the measurement parameters that minimized the mean square error of the fit obtained from the experimental data with respect to the reference fit.The authors are very grateful to the Generalitat Valenciana for its economic support in form of Vali+d grant (Ref: ACIF-2013-268).Giner Sanz, JJ.; Ortega Navarro, EM.; Pérez-Herranz, V. (2015). Optimization of the electrochemical impedance spectroscopy measurement parameters for PEM fuel cell spectrum determination. Electrochimica Acta. 174:1290-1298. https://doi.org/10.1016/j.electacta.2015.06.106S1290129817

Montecarlo based quantitative Kramers-Kronig test for PEMFC impedance spectrum validation

Electrochemical Impedance Spectroscopy (EIS) is a very powerful tool to study the behaviour of electrochemical systems. At present, it is widely used in the fuel cell field in order to study challenging cutting edge issues as membrane drying or gas diffusion layer flooding amongst others. The proper analysis of impedance data requires the fulfilment of four fundamental conditions: causality, linearity, stability and finiteness. The non compliance with any of these conditions may lead to biased, or even misguided, conclusions. Therefore it is critical to verify the compliance of these conditions before accepting any analysis performed on an experimental spectrum. This is even more important in a fuel cell experimental spectrum analysis, since fuel cells are markedly non stationary systems. The aim of this work is to establish an impedance spectrum quantitative validation technique to validate the whole experimental spectrum and to identify the individual points within a spectrum that do not comply any of the four conditions, in order to remove these inconsistent points from the analysis. The designed validation method consists in a Kramers Kronig (KK) validation test, by equivalent electrical circuit fitting, coupled with a Montecarlo error propagation method. In a first step, the experimental spectrum is fitted to a particular electrical equivalent circuit, which satisfies the KK relations. Then, in a second step, a statistical Montecarlo method is used in order to propagate the model fitting parameter uncertainty through the model. Using this approach, a consistency region is built for a given confidence level: the experimental points inside this region are considered consistent for the given confidence level, whereas the outside points are rejected. The method was used on PEMFC experimental impedance spectra; and it successfully managed to identify inconsistent points, associated to no stationarities.The authors are very grateful to the Generalitat Valenciana for its economic support in form of Vali+d grant (Ref: ACIF-2013-268).Giner Sanz, JJ.; Ortega Navarro, EM.; Pérez-Herranz, V. (2015). Montecarlo based quantitative Kramers-Kronig test for PEMFC impedance spectrum validation. International Journal of Hydrogen Energy. 40(34):11279-11293. https://doi.org/10.1016/j.ijhydene.2015.03.135S1127911293403

Protecting biodiversity in areas beyond national jurisdiction: An earth system governance perspective

In September 2018, following over a decade of informal discussions, the United Nations General Assembly launched an intergovernmental conference to address the conservation and sustainable use of biodiversity beyond national jurisdiction. This process is scheduled to take two years and is structured around four themes: marine genetic resources, area-based management tools (including marine protected areas), environmental impact assessments, and capacity building and marine technology transfer. This Perspective draws on the earth system governance literature and the authors’ own experience of and views on the BBNJ process to provide insights and recommendations for the ongoing negotiations. It highlights three areas of concern: (i) the politicization of science and coping with scientific uncertainty, (ii) institutional fragmentation; and (iii) the need for a new agreement to respond to the complex set of multiple, multilevel, and systemic threats to marine biodiversity beyond national jurisdiction

Protecting biodiversity in areas beyond national jurisdiction: An earth system governance perspective

In September 2018, following over a decade of informal discussions, the United Nations General Assembly launched an intergovernmental conference to address the conservation and sustainable use of biodiversity beyond national jurisdiction. This process is scheduled to take two years and is structured around four themes: marine genetic resources, area-based management tools (including marine protected areas), environmental impact assessments, and capacity building and marine technology transfer. This Perspective draws on the earth system governance literature and the authors’ own experience of and views on the BBNJ process to provide insights and recommendations for the ongoing negotiations. It highlights three areas of concern: (i) the politicization of science and coping with scientific uncertainty, (ii) institutional fragmentation; and (iii) the need for a new agreement to respond to the complex set of multiple, multilevel, and systemic threats to marine biodiversity beyond national jurisdiction

Genomewide analysis of PRC1 and PRC2 occupancy identifies two classes of bivalent domains

10.1371/journal.pgen.1000242PLoS Genetics410e100024