Study on the performance and mechanism of verapamil degradation by zero-valent iron activated persulfate oxidation

The current geometric increase in the global deployment of solar photovoltaic (PV) modules, both at utility-scale and residential roof-top systems, is majorly attributed to its affordability, scalability, long-term warranty and, most importantly, the continuous reduction in the levelized cost of electricity (LCOE) of solar PV in numerous countries. In addition, PV deployment is expected to continue this growth trend as energy portfolio globally shifts towards cleaner energy technologies. However, irrespective of the PV module type/material and component technology, the modules are exposed to a wide range of environmental conditions during outdoor deployment. Oftentimes, these environmental conditions are extreme for the modules and subject them to harsh chemical, photo-chemical and thermo-mechanical stress. Asides from manufacturing defects, these conditions contribute immensely to PV module’s aging rate, defects and degradation. Therefore, in recent times, there has been various investigations into PV reliability and degradation mechanisms. These studies do not only provide insight on how PV module’s performance degrades over time, but more importantly, they serve as meaningful input information for future developments in PV technologies, as well as performance prediction for better financial modelling. In view of this, prompt and efficient detection and classification of degradation modes and mechanisms due to manufacturing imperfections and field conditions are of great importance towards minimizing potential failure and associated risks. In the literature, several methods, ranging from visual inspection, electrical parameter measurements (EPM), imaging methods, and most recently data-driven techniques have been proposed and utilized to measure or characterize PV module degradation signatures and mechanisms/pathways. In this paper, we present a critical review of recent studies whereby solar PV systems performance reliability and degradation were analyzed. The aim is to make cogent contributions to the state-of-the-art, identify various critical issues and propose thoughtful ideas for future studies particularly in the area of data-driven analytics. In contrast with statistical and visual inspection approaches that tend to be time consuming and require huge human expertise, data-driven analytic methods including machine learning (ML) and deep learning (DL) models have impressive computational capacities to process voluminous data, with vast features, with reduced computation time. Thus, they can be deployed for assessing module performance in laboratories, manufacturing, and field deployments. With the huge size of PV modules’ installations especially in utility scale systems, coupled with the voluminous datasets generated in terms of EPM and imaging data features, ML and DL can learn irregular patterns and make conclusions in the prediction, diagnosis and classification of PV degradation signatures, with reduced computation time. Analysis and comparison of different models proposed for solar PV degradation are critically reviewed, in terms of the methodologies, characterization techniques, datasets, feature extraction mechanisms, accelerated testing procedures and classification procedures. Finally, we briefly highlight research gaps and summarize some recommendations for the future studies.

Electrochemical cycling induced mechanical damage of electrode materials actively contributes towards the performance degradation of lithium-ion batteries. The correlation between mechanical damage and performance degradation in anode materials that show large volume changes, such as silicon, graphite and tin, has been amply demonstrated. On the hand, typical oxide electrodes undergo only a few % volume changes, and the non-reversible nature of the crystal structure evolution as a function of lithium concentration in such electrodes is, in general, believed to be the limiting factor for performance degradation. For example, cycling in LixCoO2 is generally limited to 0≤x≤0.5, mainly, due to the irreversibility associated with the crystal structure changes beyond further Li extraction/re-insertion. However, due to their brittle nature only a few % volume changes can have significant implication on the mechanical damage leading to performance degradation for such ceramic oxide electrodes. Thus, the issue of electrochemical cycling induced mechanical degradation in oxide electrodes is being actively explored in recent years [1-2]. In this work, we present in-situ stress evolution of i) two canonical cathode systems, namely layered LiCoO2 and spinel LiMn2O4 and ii) one conversion electrode system, Co3O4 in thin film configuration to quantify the driving force leading to the mechanical degradation. In-situ stress evolution in thin film electrodes was measured by monitoring the change in the elastic substrate curvature during electrochemical cycling in a suitably designed beaker cell using multiple-beam optical sensing (MOS) method. Thin films of the electrodes were prepared using solution deposition technique. Structural characterizations using XRD and Raman spectroscopy showed predominant presence of desired (poly)crystalline phases in the as prepared samples. In addition, SEM images also revealed the presence of dense microstructural features in the as prepared films. During Li-extraction from layered LixCoO2, there was almost linear increase in compressive stress up to ~50% Li removal, which is consistent with its lattice parameter evolution during Li removal [3], and a maximum compressive stress of ~0.35 GPa was observed for x~0.5. Upon lithiation there was almost reversible stress evolution in LixCoO2. Similar behavior was also observed for subsequent cycles as well, while limiting the upper charging cut-off voltage to 4.3V. On the other hand, initial delithiation from spinel LixMn2O4 induces tensile stress up to ~4.1V, beyond which the induced stress reverses direction (termed as “compressive drop”) with further delithiation (up to 4.3 V). This reversal of stress evolution in the later stages of delithiation from spinel LixMn2O4 is in apparent contradiction with the lattice parameter evolution of spinel LixMn2O4 during lithium extraction [4]. Upon lithium re-insertion (up to 3.5V), induced compressive stress increases linearly. The subsequent cycles (in the 4V region), however, did not show any “compressive drop” during later stages of delithiation and the induced stress evolved reversibly during delithiation-lithiation. The origin of this first cycle “compressive drop” in spinel LiMn2O4 is not known at present. In an attempt to establish the origin of the observed first cycle “compressive drop” in spinel LiMn2O4 thin films, stress measurement data varying multiple parameters including cathode film thickness, reannealing a cycled electrode will be presented. The effect of stress evolution in these thin film electrodes during cycling as a function of cycling voltage window and current density will also be presented and discussed in the light of their crystal structural changes. References D. J. Miller, C. Proff, J. G. Wen, D. P. Abraham and J. Bareno, Adv. Energy Mater., 3, 1098 (2013).W. H. Woodford, W. C. Carter and Y. M. Chiang, Energy Environ. Sci., 5, 8014 (2012).J. N. Reimers and J. R. Dahn, J. Electrochem. Soc., 139, 2091 (1992).Y. Xia and M. Yoshio, J. Electrochem. Soc., 143, 825 (1996).

High cost and performance degradation are still the main issues which hinder the commercialization of low temperature fuel cells on a grand scale [1]. Both of these issues are closely related to the catalyst which accounts for up to 40% of the PEMFC stack cost [2] while the loss of electrochemically active surface area (ECSA) poses a major contribution to the overall performance degradation. Furthermore, chemical membrane degradation is another main issue as membrane thinning and pinhole formation are limiting the lifetime of the cells. Detailed physical models provide a better understanding of the underlying mechanisms leading to these degradation mechanisms and therefore can help in developing strategies to increase the durability of the cells. Here we present a two-step approach to achieve this goal. First we develop a transient, two-dimensional single cell model, which includes all relevant mechanisms to describe the cell performance, i.e., electrochemistry, two-phase multi-component transport in the porous layers, charge and heat transport as well as water and gas permeation through the membrane. This model is implemented in our in-house code NEOPARD-X which is based on the open-source framework DuMux [3]. It provides important insights on the local conditions within the cell which are often not accessible in experiments but determine the local degradation rates. In particular we discuss the water management and how simulations of electrochemical impedance spectra (EIS) can be used for process identification. In the second step we discuss detailed physical models for the degradation mechanisms. A multi-step chemical membrane degradation model is presented which incorporates the formation and decomposition of hydrogen peroxide, iron ion redox cycle, radical formation and degradation via “unzipping” and “side chain scission” mechanism. The model provides insights on the local degradation rates depending on the operating conditions. Strongest degradation is obtained at the anode side during OCV while at higher current densities the degradation is strongly reduced and shifts to the cathode side (left figure). The model is validated with fluoride emission rate (FER) measurements under various operating conditions. Finally, a catalyst degradation model due to platinum dissolution and particle growth is discussed. Since the dissolution kinetics strongly depends on the platinum oxide coverage, a platinum oxide model has been developed and validated with dedicated CV experiments. This model is able to describe the experimentally observed logarithmic growth of the oxide coverage. This coverage affects the surface energy of the particles and thus influences the platinum dissolution. Therefore, taking into account the kinetics of the oxide formation is crucial for describing the catalyst degradation under dynamic operating conditions such as fast potential cycling which is typically used as an AST for the catalyst. By coupling the degradation model to the single cell model we investigate the catalyst degradation in AST and long-term degradation tests. The degradation model is validated with experimental data for the ECSA loss during these tests as well as with particle size distributions (PSD) obtained with TEM (right figure). The occurrence of heterogeneities in the catalyst degradation is discussed. Figure: simulated local FER (mol m-3 s-1) due to chemical membrane degradation at various cell voltages (a); comparison between simulated and measured catalyst PSD evolution (b). Figure 1

Solid oxide fuel cell (SOFC) performance degradation analysis and optimization studies are important prerequisites for its commercialization. Reviewing and summarizing SOFC performance degradation studies can help researchers identify research gaps and increase investment in weak areas. In this study, to help researchers purposely improve system performance, degradation mechanism analysis, degradation performance prediction, and degradation performance optimization studies are sorted out. In the review, it is found that the degradation mechanism analysis studies can help to improve the system structure. Degradation mechanism analysis studies can be performed at the stack level and system level, respectively. Degradation performance prediction can help to take measures to mitigate degradation in advance. The main tools of prediction study can be divided into model-based, data-based, electrochemical impedance spectroscopy-based, and image-based approaches. Degradation performance optimization can improve the system performance based on degradation mechanism analysis and performance prediction results. The optimization study focuses on two aspects of constitutive improvement and health controller design. However, the existing research is not yet complete. In-depth studies on performance degradation are still needed to achieve further SOFC commercialization. This paper summarizes mainstream research methods, as well as deficiencies that can provide partial theoretical guidance for SOFC performance enhancement.

11 - Performance degradation and failure mechanisms of fuel cell materials

Performance degradation remains as one of the primary limitations for practical applications of proton exchange membrane (PEM) fuel cells. The performance of a PEM fuel cell stack is affected by many internal and external factors, such as fuel cell design and assembly, degradation of materials, operational conditions, and impurities or contaminants. Performance degradation is unavoidable, but the degradation rate can be minimized through a comprehensive understanding of degradation and failure mechanisms. In present work, a single PEM fuel cell for stationary applications is investigated. Membrane and catalyst layers (anode and cathode electrodes) are considered as critical components that affect the degradation of the cell. The model used in this work diagnoses degradation of MEA (platinum degradation in catalyst layers and membrane thinning and dehydration in polymer membrane), and by considering the degradation over operating time, estimates power density over system lifetime. In this paper, also three optimization model with different objective functions are developed tomaximize total energy production. The results show that by continuously optimizing the operating conditions, total energy generation of the system will increase up to 3.16 %.

Effect of pH and Cl- concentration on the electrochemical oxidation of pyridine in low-salinity reverse osmosis concentrate: Kinetics, mechanism, and toxicity assessment

The role of dissolved oxygen in the sulfite/divalent transition metal ion system: degradation performances and mechanisms

Fuel gas utilization and water management are particularly challenging integrated engineering problems in hydrogen–oxygen proton exchange membrane fuel cell (H2/O2 PEMFC) systems. Herein, a standardized process is adopted to evaluate the performance and investigate the degradation mechanisms of a PEMFC with dual exhaust gas recirculation. The purpose of incorporating recirculation subsystems in the fuel cell is to achieve a high fuel gas utilization rate and realize effective water management inside the stack, which consists of 3D‐printed ejectors and a customized recirculation pump. Evaluation of the electrochemical performance degradation and morphological characterization of the fuel cells under different operating strategies are performed after 50 h durability experiments. At a current density of 400 mA cm−2, the performance degradation rates of the stack decrease from 16.50% to 7.49% and 0.71% in the ejector and recirculation pump operation strategies, respectively. The results show that using exhaust gas recirculation devices (ejector/pump) in the fuel cell stack can help in effectively mitigating water flooding and chemical degradation of the membrane electrode assembly. The findings of the study provide a perspective on the exhaust gas recirculation behavior and contribute to the engineering application of H2/O2 PEMFCs.

Solid oxide fuel cell (SOFC) system becomes one of the most promising power generation devices for its high efficiency and low emission. However, the commercialization process of SOFC is restricted due to the problems of life-span and cost, so the performance degradation and fault mechanisms of SOFC systems are partially studied by some scholars. An SOFC system model that efficiently describes system performance degradation and various faults characteristics during long term operation plays pivotal role in improving system performance and extending life time. In this paper, a high fidelity steam-reforming SOFC system model incorporating system performance degradation principles and faults evolving mechanisms is developed based on physical laws and validated with experimental data. With this model the drifting of static optimal operation point (OOP) caused by performance degradation and different fault combinations, together with system input sensitivity analysis are investigated. The results indicate that the introduction of the degradation and fault mechanisms would increase the accuracy of the system model, and decrease system electrical efficiency. The steam-reforming SOFC system has a higher sensitivity to the stack fault than to the reformer fault.

Recycling plastic waste by mix with natural polymers for bio-plastic packaging produces plastics with high mechanical properties and easily degradable. In this study, the relation between the structural and the optical properties of composite SPF/starch/chitosan/polypropylene to the mechanical properties and degradation performance were analyzed. Structural and optical properties of composite bioplastic SPF/Starch/Chitosan/Polypropylene have analyzed using X-Ray diffraction (XRD), and Fourier transforms infrared (FTIR) spectroscopy, respectively. The composition was varied: the ratio between starch and chitosan are 35/65, 50/50, and 65/35 with additional SPF for each ratio is 1%, 3%, and 5%. The SPF effectively enhances the tensile strength due to the SPF's better dispersion and interaction in the starch/chitosan/polypropylene matrix. For SPF's effect on the degradation performance, the ratio starch/chitosan 50/50 increase for 1% SPF is 87.23%, for 3% SPF is 92.59%, and for 5 SPF is 94.12%. The refractive index (n), extinction coefficient (k), dielectric functions (e), and energy loss function (Im (−1/ e)) determined from the quantitative analysis of FTIR spectra by using Kramers–Kronig (K–K) relations. The crystalline phase increases with increasing the amount of SPF in composite bioplastic SPF/Starch/Chitosan /Polypropylene for ratio starch/chitosan is 35/65, which consistent with the distance between the wavenumber (D) of transversal and longitudinal optical phonon vibration mode become wider. We found that a good correlation between optical properties, structural properties, mechanical properties, and degradation performance for ratio starch/chitosan 35/65 and 50/50 with SPF 1% and 3% in the composite. Besides, the FTIR spectra could be useful for determining the optical phonon vibration, dielectric function, and energy loss function of composite bioplastic SPF/Starch/Chitosan /Polypropylene. The degradation performance by additional polypropylene from plastic waste shows a potential solution for decreasing plastic waste in the world.

The required target for mass deployment of PEMFC in different applications is still not fully achieved, because of a severe performance decay, determined by the interaction of several degradation mechanisms [1]. The comprehension of such mechanisms and the influence of operating condition stressors is still not satisfactory to accurately predict fuel cell lifetime during real operation. Especially the components structural and functional alteration in time, observed by ex-situ techniques, can be hardly associated to a distinct contribution to performance loss. Electrochemical impedance spectroscopy is a promising in-situ technique to distinguish the contributions of different degradation phenomena, but nowadays data analysis is widely performed modelling the fuel cell through simplified electrical circuits that do not permit to achieve a solid physical interpretation of performance degradation causes. A physically based modelling approach, recently explored in the literature [2,3], can cover this gap, however it is not fully consolidated yet and the required effort to develop appropriate tools limits today its utilization to modelling experts. The present work aims at presenting the effectiveness of an approach that combines experimental and physically based modelling analysis of electrochemical impedance in investigating performance degradation occurring in different technologies [4-7]: HT-PEMFC, Low-Pt PEMFC, DMFC, PGM-free PEMFC. The general methodology is presented, highlighting the possible onset of different regimes, where distinct phenomena prevail. The continuum model based on macro-homogenous assumption, solves mass and ionic conservation coupled with Stefan-Maxwell diffusion and Ohm’s law; electrochemical reactions are described with Butler-Volmer kinetics. EIS is solved according to the approach reported in [5]. Subsequently some relevant cases are discussed in details, emphasizing the influence of heterogeneous degradation [5] and local mass transport [7]. One analysis reported in this work is the effect of heterogeneity of ageing on EIS, which determine an increase of the cathodic charge transfer resistance that is not ascribed to a loss of electrochemical active surface, but to the uneven distribution of the reaction rate. Another analysis reported in this work consists in the simulation of EIS with commercial CFD codes: the effect of 3D geometrical features was analyzed, e.g bends in the flow field, flow bypass between channels, interdigitated flow pattern. [1] Boroup, R., & al. (2007). Scientific aspects of Polymer Electrolyte Fuel Cell durability and degradation. Chemical Reviews, 107, 3904-3951. [2] Baricci, A., Zago, M., & Casalegno, A. (2014). A quasi 2D model of a High Temperature Polymer Fuel Cell for the interpretation of impedance spectra. Fuel Cells, 14, 926-937. [3] Kulikovsky, A.A., (2012). A physical model for catalyst layer impedance. Journal of Electroanalytical Chemistry, 669, 28-34 [4] Bresciani, F., Casalegno, a., Zago, M., & Marchesi, R. (2013). A parametric analysis on DMFC anode degradation. Fuel Cells, 14, 386–394. [5] Baricci, A., Zago, M., & Casalegno, A. (2016). Modelling analysis of heterogeneity of ageing in high temperature polymer electrolyte fuel cells: insight into the evolution of electrochemical impedance spectra. Electrochimica Acta, 222, 596–607. [6] Casalegno, A., Baricci, A., Bisello, A., Odgaard, M., Serov, A., & Atanassov, P. (2017). Insight into degradation mechanism in non-precious metal composite catalysts for PEMFC. 7th FDFC, Stuttgart. [7] Baricci, A., Mereu, R., Messaggi, M., Zago, M., Inzoli, F., & Casalegno, A. (2017). Modeling analysis of flow field geometrical features in Polymer Electrolyte Fuel Cells porous media. 7th FDFC, Stuttgart.

Monitoring of Photovoltaic System Performance Using Outdoor Suns-VOC

As an important part of high-speed train (HST), the mechanical performance of bogies imposes a direct impact on the safety and reliability of HST. It is a fact that, regardless of the potential mechanical performance degradation status, most existing fault diagnosis methods focus only on the identification of bogie fault types. However, for application scenarios such as auxiliary maintenance, identifying the performance degradation of bogie is critical in determining a particular maintenance strategy. In this article, by considering the intrinsic link between fault type and performance degradation of bogie, a novel multiple convolutional recurrent neural network (M-CRNN) that consists of two CRNN frameworks is proposed for simultaneous diagnosis of fault type and performance degradation state. Specifically, the CRNN framework 1 is designed to detect the fault types of the bogie. Meanwhile, CRNN framework 2, which is formed by CRNN Framework 1 and an RNN module, is adopted to further extract the features of fault performance degradation. It is worth highlighting that M-CRNN extends the structure of traditional neural networks and makes full use of the temporal correlation of performance degradation and model fault types. The effectiveness of the proposed M-CRNN algorithm is tested via the HST model CRH380A at different running speeds, including 160, 200, and 220 km/h. The overall accuracy of M-CRNN, i.e., the product of the accuracies for identifying the fault types and evaluating the fault performance degradation, is beyond 94.6% in all cases. This clearly demonstrates the potential applicability of the proposed method for multiple fault diagnosis tasks of HST bogie system.

Pure zero-valent iron (ZVI) was supported on silica and starch to enhance the activation of persulfate (PS) for tetracycline degradation. The synthesized catalysts were characterized by microscopic and spectroscopic methods to assess their physical and chemical properties. High tetracycline removal (67.55%) occurred using silica modified ZVI (ZVI-Si)/PS system due to the improved hydrophilicity and colloidal stability of ZVI-Si. Incorporating light into the ZVI-Si/PS system improved the degradation performance by 9.45%. Efficient degradation efficiencies were recorded at pH 3-7. The optimum operating parameters determined by the response surface methodology were PS concentration of 0.22mM, initial tetracycline concentration of 10mg/L, and ZVI-Si dose of 0.46g/L, respectively. The rate of tetracycline degradation declined with increasing tetracycline concentration. The degradation efficiencies of tetracycline were 77%, 76.4%, 75.7%, 74.5%, and 73.75% in five repetitive runs at pH 7, 20mg/L tetracycline concentration, 0.5g/L ZVI-Si dose, and 0.1mM PS concentration. The degradation mechanism was explained, and sulfate radicals were the principal reactive oxygen species. The degradation pathway was proposed based on liquid chromatography-mass spectroscopy. Tetracycline degradation was favorable in distilled and tap water. The ubiquitous presence of inorganic ions and dissolved organic matter in the lake, drain, and seawater matrices interfered with the tetracycline degradation. The high reactivity, degradation performance, stability, and reusability of ZVI-Si substantiate the potential practical application of this material for the degradation of real industrial effluents.