Simulation of Electrochemical Impedance Spectra of Solid Oxide Fuel Cells Using Transient Physical Models

A general electrochemical impedance spectroscopy ͑EIS͒ modeling approach by directly solving a one-dimensional transient model based on physical conservation laws was applied for simulating EIS spectra of an anode-supported solid oxide fuel cell ͑SOFC͒ button cell consisting of Ni-yttria-stabilized zirconia ͉Ni-scandia-stabilized zirconia ͑ScSZ͉͒ScSZ͉lanthanum strontium manganate ͑LSM͒-ScSZ multiple layers. The transient SOFC model has been solved for imposed sinusoidal voltage perturbations at different frequencies. The results have then been transformed into EIS spectra. Six parameters had to be tuned ͑three for the cathode and three for the anode͒ and have been estimated using data from a symmetric cathode cell and from a button cell. The experimental and simulated EIS spectra were in good agreement for a range of temperatures ͑750-850°C͒, of feed compositions ͑mixture of H 2 /H 2 O/N 2 ͒, and of oxidants ͑air and oxygen͒. This approach can help in interpreting EIS spectra, as illustrated by identifying the contribution of transport limitation. Fuel cell electrochemical systems are usually complex and are governed by coupled physicochemical processes such as chemical and electrochemical reactions, charge transport, and mass transport. 1,2 Because polarization curves can only provide a general description of the cell performance, electrochemical impedance spectroscopy ͑EIS͒ has become widely used in fuel cell research and development because it involves a relatively simple electrical measurement that gives detailed information about the fuel cell system, from mass-transport properties, chemical reaction rates, and dielectric properties to defects, microstructure, compositional influences, etc. 3 In this dynamic technique, usually a voltage perturbation is applied to a system and the amplitude and phase shift of the resulting current response are measured. Measurements can be conducted over a wide range of frequencies, resulting in the construction of impedance spectra. 5 Although the approach is useful and quite powerful, it often has limitations such as: 1. The approach can lead to ambiguities in data interpretations because the equivalent circuits are seldom unique except for only the simplest circuits. An equivalent circuit involving several circuit elements could often be rearranged in various configurations while still yielding the same impedance. 2. Detailed physical and chemical processes in the system cannot be predicted by equivalent-circuit models. For instance, the effects of current distributions and concentration distributions cannot be taken into account when interpreting data from equivalent-circuit models. 3. The measured system could only be approximated by circuit elements when assuming linear response of the system. The impedance is supposed to be independent of the amplitude of the applied signals. However, the electrochemical system could be highly nonlinear, especially for sinusoidal perturbations with high amplitudes. It was suggested that nonlinear EIS ͑NLEIS͒ measurements have several potential advantages. To investigate solid oxide fuel cell ͑SOFC͒ electrode reaction kinetics, Miterdorfer and Gauckler 7-9 used a state-space model ͑SSM͒, which is widely used in control theory for solving complex differential equations. Bieberle and Gauckler 5 studied in depth elementary electrochemical reactions in SOFC anode by both experimental and SSM approaches. To simulate the electrochemical impedance spectra, the models were solved directly through the SSM approach. Bessler 10 presented a computational method for simulating EIS spectra based on transient numerical simulations of the reaction system. The impedance was then calculated in the time domain from the simulated periodic response of the system, maintaining its full nonlinear response. This method has been further validated by detailed modeling studies on SOFC EIS spectra achieved from gas-transport processes. 11 Gewies et al. 12 also applied this method on Ni/yttria-stabilized zirconia ͑YSZ͒ cermet anodes. Zhu and Kee 13 developed a time-accurate model to analyze EIS spectra in anode-supported button cells with internal methane reforming. This model represented significant advantages regarding physical conservation laws, porous media transport within the electrode, and heterogeneous chemistry reactions mechanisms, all of those being solved in the time domain. However, the spatial variations of ion and electron transport throughout the electrode structures were not considered. In this paper, a general approach for EIS spectra simulation is applied by solving a comprehensive set of coupled transient models based on physical conservation laws. This simulation approach is illustrated by considering a transient model of an anode-supported SOFC button cell consisting of Ni-YSZ͉Ni-scandia-stabilized zirconia ͑ScSZ͉͒ScSZ͉LSM-ScSZ multiple layers. The simulation results of the EIS spectra were then compared to the measured EIS spectra under various conditions to prove the validity of both the transient model and the EIS simulation approach. Experimental Testing cell.-The anode-supported SOFC button cell used in this study consisted of a Ni/YSZ anode support layer ͑680 m͒, a Ni/ScSZ anode active interlayer ͑15 m͒, a ScSZ thin-film electrolyte layer ͑20 m͒, and a lanthanum strontium manganate ͑LSM͒/ ScSZ cathode layer ͑15 m͒. 14,1

Predictive value of volumetric parameters based on 18F-PSMA-1007 PET/CT for prostate cancer metastasis

Purpose of the reportTo explore the value of 18F-labeled prostate-specific membrane antigen (PSMA-1007) positron emission tomography (PET)/computed tomography (CT), the maximum standardized uptake value (SUVmax) of the primary tumor, prostate PSMA-tumor volume (PSMA-TVp), and prostate total lesion PSMA (TL-PSMAp) for predicting prostate cancer (PCa) metastasis and follow-up evaluation in primary PCa lesions.Materials and methods18F-PSMA-1007 PET/CT data of 110 consecutive newly diagnosed PCa patients were retrospectively analyzed. Patients were divided into non-metastatic, oligometastatic, and extensive metastatic groups. The predictive power was assessed using the receiver operating characteristic curve. Multi-group one-way analysis of variance and post-hoc tests were used to compare the groups. Patients were monitored post-therapy to evaluate treatment effectiveness.ResultsAmong the 110 patients, 66.4% (73) had metastasis (29 oligometastatic, 44 extensive metastasis). AUCs for Gleason score (GS), total prostate-specific antigen(TPSA), SUVmax, TL-PSMAp, and PSMA-TVp were 0.851, 0.916, 0.834, 0.938, and 0.923, respectively. GS, TPSA, SUVmax, TL-PSMAp, and PSMA-TVp were significantly different among the groups. In the post-hoc tests, differences in GS, TPSA, SUVmax, TL-PSMAp, and PSMA-TVp between the non-metastatic and oligometastatic groups and non-metastatic and extensive metastatic groups were significant (P<0.010). Differences in TL-PSMAp and PSMA-TVp between oligometastatic and extensive metastatic groups were significant (P=0.039 and 0.015, respectively), while those among GS, TPSA, and SUVmax were not. TL-PSMAp and PSMA-TVp distinguished between oligometastatic and extensive metastases, but GS, TPSA, and SUVmax did not. In individuals with oligometastasis, the implementation of active treatment for both primary and metastatic lesions may result in a more favorable prognosis.Conclusions18F-PSMA-1007 PET/CT volumetric parameters PSMA-TVp and TL-PSMAp can predict PCa oligometastasis

Recovery of high purity copper from waste printed circuit boards of mobile phones by slurry electrolysis with ammonia-ammonium system

Waste printed circuit boards (WPCBs) are identified to be the most complex recycling materials among waste electrical and electronic equipment (WEEE). Slurry electrolysis with acidic system can directly separate and recover copper from WPCBs while current efficiency and purity were generally reduced due to deposition of impurity metals and the hydrogen evolution during recovery process. In ammonia-based system, copper can be selectively extracted and copper (II) ammine complexes generally react with metallic copper to form copper (I) ammine complexes, promoting current efficiency and purity. Therefore, an efficient ammonia-ammonium carbonate slurry electrolysis system is proposed for high purity copper recycling from waste printed circuit boards of mobile phones (WPCB-MPs). The factors affecting copper current efficiency and recovery rate are systematically discussed. These results indicate that appropriate increasing NH3 center dot H2O, (NH4)2CO3, Cu2+, NaCl concentration, solid-to-liquid ratio, current density and reaction time could effectively increase copper recovery rate and current efficiency. The current efficiency and recovery rate of copper are 95.2 and 90.4%, respectively under the optimum test conditions of 20 g/L Cu2+, 0.25 mol/L (NH4)2CO3, 4 mol/L NH3 center dot H2O, 30 g/L solid-to-liquid ratio, 1 mol/L NaCl, 20 mA/cm2, 3 h. Moreover, copper could be recovered at the cathode with a purity of 99.97%. Compared with acidic system, this study provides an efficient approach to recover high purity copper from WPCB-MPs, showing a prospective future for WEEE resource recycling

Waste Electrical and Electronic Equipment Reutilization in China

Waste electrical and electronic equipment (WEEE), also called electronic waste or e-waste, the core of "urban mining ", is attracting more and more attention to its pollution control and circular recycling. Hence, we defined WEEE, preliminarily discussed its history in China and pointed out that China has made great achievements in WEEE circular reutilization and pollution control. Meanwhile, we analyzed the four levels of circular WEEE recycling: repair, reuse and remanufacture, waste-to-materials, waste-to-products and waste-to-energy, and also put forward questions during this process. Moving forward, WEEE management will turn to intelligent management targeted on hazardous waste and other pollution, not merely the guidelines. Meanwhile, WEEE technology will transfer to value-added and automated reutilization, not just simple dismantling.</p

Erratum to: Guidelines for the use and interpretation of assays for monitoring autophagy (3rd edition) (Autophagy, 12, 1, 1-222, 10.1080/15548627.2015.1100356

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Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition)

In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for bona fide autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field