PEMFC impedance spectroscopy using synthetic wide-band signals

The “state of health” of a fuel cell can be determined by the study of its complex impedance in a frequency domain, usually using impedance spectroscopy (IS) method. In our days, to characterize a PEM using this method, a sine signal sweep is used. The IS is based on the complex measurement of the impedance of a cell along a frequency domain, depending on the electrochemical state of the cell. The main advantage of the IS is the faithfulness between its results and the theoretical ones. These results are analyzed using the electrical Randles model. Our work presents an innovative method to measure the IS. It introduces a system to dramatically reduce the measurement time using as an alternative of the sine signal, a frequency domain synthetic wide-band signal. During the tests, a theoretical wide-band signal is built in the frequency domain. The signal is converted into a temporal one and is used as a stimulus for the fuel cell. The response in terms of cell voltage is captured and the impedance measured. This answer is defined in the same frequency range than the stimulus. The time required for the measurement corresponds to the time of the stimulus and it is in the range of the lower cut-off frequency. The system used as test-bench is composed by an electronic circuit and a PC based software for the signal analysis. This system was built and tested with good results using a PEMFC.     

A multidimensional approach for CSR assessment: The importance of the stakeholder perception

“If a tree falls in the forest and no one is around to hear it, does it make a sound?” and, paraphrasing the proverbial philosophy question, if a company has a strong CSR commitment but nobody recognizes it, does it produce any benefits? Business returns from corporate social responsibility (CSR) practices, such as customers loyalty and company reputation, depend heavily on how stakeholders perceive the company social behavior, making the measure of stakeholder perception a key issue in the process of CSR assessment. In this paper the analysis of CSR activities, as perceived by stakeholders, is realized utilizing global reporting initiative (GRI) indicators structured under balanced scorecard (BSC) perspectives and sustainability dimensions. We utilize a multi-criteria approach combined with fuzzy linguistic variables, in the variation of the 2-tuple, creating a hierarchy of CSR components with the purpose of integrating financial and non-financial sustainability dimensions and strategic perspectives. The hierarchy provides a multidimensional model that allows to evaluate the multifaceted social behavior of a company: the same company can be perceived simultaneously as responsible or irresponsible depending on the considered dimension and perspective.