1,720,997 research outputs found
Among old materials and different approaches to enhance stability and electrochemical activity of Solid Oxide Cells
No full textPerovskite materials are widely studied as cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFC) for their relevant properties regarding electrocatalytic activity or stability. Nevertheless, a material that combines both it is not yet available. Among them, La1-XSrxMnO3 (LSM), La1-xSrxCo1-yFeyO3 (LSCF), Ba1-xSrxCo1-yFeyO3 (BSCF), La1-xSrxFeO3 (LSF), La1-xBaxCoO3 (LBC), were deeply investigated but their properties are not completely exploited or optimized.
In this PhD project all the reported electrode materials are investigated using different approaches. The study starts from LSM – based electrodes, which show a change in kinetic mechanism under particular operating conditions. These results open new horizons about the employment of this material, up today considered not suitable for IT-SOFC temperature range. A first application, with promising results, is proposed here with a LSM infiltration in LSCF and BSCF scaffold. The presence of infiltrated-phase enhance stability and electrochemical activity of electrodes.
Promising results are obtained also by mixing BSCF and LSCF powders. Three different BSCF:LSCF ratio are considered to produce three different cathodes. All the new compositions show an improvement of activity for oxygen reduction reaction, with very competitive values of polarization resistance. Moreover, one of these new electrodes has also a lowering of degradation rate compared with reference materials
In the last year of this project, other two materials are combined and their interactions investigate. LSF, providing a high stability, is coupled with LBC, which has a really high surface electrocatalytic activity. The two materials are tested in different thin film systems. When they are mixed before the sintering stage react forming a new perovskite phase (Ba0.099Sr0.297La0.594Fe0.8Co0.2O3), with a higher activity. The reaction is avoided producing a bilayer system, and the presence of LBC top layer over a LSF dense thin film drastically reduces polarization resistance, highlighting promising results
Tra vecchi materiali e diversi approcci per migliorare la stabilità e l’attività elettrochimica delle cella ad ossido solido
No full textLe celle ad ossidi solidi (SOC), siano esse celle combustibili (SOFC) o elettrolizzatori (SOEC), sono una tecnologia in grado di fornire risposte concrete alla rivoluzione energetica attualmente in corso. Tuttavia perché i loro indiscussi vantaggi, quali il ridotto impatto ambientale, la flessibilità al carico e la modularità, diventino competitivi con le tecnologie maggiormente consolidate sul mercato, è ancora necessario un ulteriore sforzo riguardo la loro durata nel tempo. Infatti alle alte temperature d’esercizio (~ 800 °C) di questi sistemi corrisponde un degrado del materiale e una perdita in performance. La via maestra per limitare questo effetto indesiderato è la riduzione della temperatura (500-700 °C); questo approccio ha come possibile conseguenza la perdita di prestazione da parte dei materiali maggiormente impiegati a temperature superiori. In particolar modo le performance e la stabilità del catodo, sede della reazione di riduzione dell’ossigeno, sono molto sensibili a questo parametro, influenzando il comportamento globale della cella. Questo scenario richiede quindi lo sviluppo di materiali stabili in grado di fornire un’attività elettrochimica performante alle temperature target della ricerca attuale. Negli ultimi anni le perovskiti (ABO3) sono una classe di materiali che si è dimostrata promettente per raggiungere questo obiettivo. Tra questi, i materiali più studiati sono La0.8Sr0.2MnO3 (LSM), La0.6Sr0.4Co0.2Fe0.8O3-δ(LSCF), Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF). I risultati riportati in letteratura hanno dimostrato come sia difficile combinare prestazione elettrochimica e durata nel tempo, e come questi soffrano o di scarse performance (LSM) o problemi di degrado non trascurabili (LSCF, BSCF). Questa tesi è nata quindi nel tentativo di investigare se mediante diversi approcci disponibili per la preparazione dell’elettrodo (infiltrazione, elettrodo composito), fosse possibile migliorare le caratteristiche richieste per un materiale catodico.
Lo studio è partito investigando il comportamento elettrochimico di elettrodi a base di LSM, un materiale considerato principalmente come conduttore elettronico. I risultati ottenuti hanno mostrato un cambiamento nel meccanismo cinetico, in funzione del sovrapotenziale applicato alla cella. Tali risultati, aprono nuovi orizzonti riguardo lo sfruttamento di questo materiale, fino ad oggi considerato non adatto per l’impiego in sistemi SOFC a temperature intermedie (IT-SOFC). Una prima applicazione, con promettenti risultati, è stata fornita eseguendo l’infiltrazione di nanoparticelle di LSM su scaffold di altri due materiali perovskitici, quali LSCF e BSCF. La presenza di queste particelle sulla superficie elettrodica ha avuto come conseguenza quella di incrementare sia stabilità che performance elettrochimica dei due materiali di partenza. Il secondo step del progetto ha considerato un elettrodo composito, costituito da un mixing di due materiali, LSCF e BSCF. Entrambi i materiali forniscono eccellenti proprietà elettrocatalitiche, ma soffrono di una certa instabilità ed elevato degrado. Con l’idea di sfruttare i punti di forza e di ottenere una mutua stabilizzazione dei due materiali, tre differenti elettrodi con differenti rapporti volumetrici BSCF:LSCF sono stati analizzati. Tutte e tre le nuove formulazioni hanno evidenziato un incremento dell’attività catalitica per la riduzione dell’ossigeno rispetto ai materiali di partenza, con valori di resistenza di polarizzazione competitivi con quelli di riferimento riportati in letteratura. Inoltre l’elettrodo con rapporto BSCF:LSCF=70:30 oltre ad avere il miglior comportamento elettrochimico, è caratterizzato da una diminuzione della velocità di degrado. Nell’ultimo anno del progetto, in collaborazione con la Technische Universitat Wien, altri due materiali sono stati accoppiati e le loro interazioni investigate. Il La0.6Sr0.4FeO3-δ (LSF), materiale molto stabile ma poco attivo, è stato combinato con il La0.6Ba0.4CoO3-δ (LBC), che fornisce un’elevatissima attività elettrocatalitica, ma soffre di instabilità. I due materiali sono stati testati in differenti sistemi a film sottile ottenuti mediante pulse laser deposition. Se mescolati prima dello step di sintering i due materiali reagiscono formando una nuova fase perovskitica attiva (Ba0.099Sr0.297La0.594Fe0.8Co0.2O3). La reazione è evitata producendo un sistema bilayer, e la presenza di un top layer di LBC sopra un film denso di LSF produce una drastica riduzione della resistenza di polarizzazione. Durante tutta la tesi particolare attenzione è stata dedicata all’integrazione di differenti approcci disponibili per analizzare i risultati sperimentali ottenuti mediante impedenza a spettroscopia elettrochimica. Hanno assunto particolare rilievo la distribuzione dei tempi di rilassamento, la simulazione con circuiti equivalenti e la modellazione basata su modelli fisici
Electrochemical oxidation of a synthetic dye using a BDD anode with a solid polymer electrolyte
No full textIn this study the performance of an electrochemical cell with a solid polymer electrolyte (SPE) has been investigated using Safranin T, a synthetic dye, as a model compound. The cell consists of a Nafion membrane sandwiched between a BDD mesh anode and a Ti/RuO2 mesh cathode operating at constant current. The effects of operating conditions such as applied current, stirring rate and electrolyte conductivity were studied. The experimental results showed that Safranin T was completely removed by reaction with [rad]OH radicals generated by water electrolysis and that the oxidation was under charge-transfer control. Furthermore, it was observed that addition of Na2SO4 to the solution decreased the removal rate but also decreased the specific energy required for the process
Electrochemical treatment of poorly biodegradable DPC cationic surfactant
No full textThe electrochemical oxidation of the cationic surfactant dodecylpyridinium chloride (DPC) was investigated using an electrolytic flow cell operating in batch recycle mode under galvanostatic conditions. The cell was equipped with a boron-doped diamond anode and a stainless steel cathode. The effects of some operating parameters, such as current density, recirculation flow-rate, and DPC concentration were investigated. DPC removal and mineralization were monitored by HPLC analyses and TOC measurements. The results show that DPC can be successfully removed and that degradation is under mass-transport control. The oxidation rate was well described by pseudo-first-order kinetics, and while the apparent rate constant increased with flow-rate, it was unaffected by DPC concentration and current density. Under optimum 5 mA cm-2 and 300 dm3 h-1 conditions, the apparent rate constant was 3.13 × 10-4 s-1. DPC solution with 75 mg dm-3 of surfactant (54 mgdm-3 of initial TOC) was completely mineralized in 330 min, achieving maximum 33% efficiency. Anodic oxidation of the cationic DPC was compared with anionic sodium dodecyl benzene sulfonate (SDBS) degradation and DPC oxidation was demonstrated to be faster and requiring less energy due to the presence of chloride ions in the DPC molecules that are oxidized to active chlorine which acts as redox mediator increasing the removal rate
Hydrogen Safety in Solid Oxide Fuel Cells: an LSTM-Based Model for Predicting Temperature Anomalies and Change Points
No full textTemperature anomalies in solid oxide fuel cells (SOFC) can significantly affect performance, induce thermal stress and evolve towards accident scenario. Accurately predicting these anomalies is critical for maintaining system integrity and safety, possibly providing weak early signals before an incident occurs. This paper presents the development of a predictive model utilizing Long Short-Term Memory (LSTM) networks to forecast temperature anomalies and detect change points between normal and abnormal states in SOFCs. The LSTM model is trained on extensive historical temperature data, capturing temporal dependencies and patterns indicative of potential anomalies. Change point detection mechanisms are integrated to identify transitions between normal and abnormal operating states, enabling timely interventions. The model efficacy in predicting temperature-related issues and detecting change points with high accuracy is verified by extensive runs in a laboratory scale plant. The results indicate that the LSTM-based model significantly outperforms traditional methods in both prediction accuracy and early anomaly detection. The research findings underscore the potential of advanced neural network architectures in predictive maintenance applications, providing a robust tool for managing performances and ensuring operational safety, in hydrogen fuel cell-power generation
Response surface methodology for low-energy consumption electro-Fenton process for xanthene dye electrochemical degradation
No full textErythrosine B (EB) is a dye widely used in the food and textile industries. Despite many studies that have been proposed in the literature about the electrochemical oxidation of dyes, few studies considered such recalcitrant xanthene compound, although it has been recognized as a threat to health and the environment. Then, this study investigates the oxidation of EB by a homogeneous electro-Fenton process using iron (II) sulfate heptahydrate as a catalyst, carbon felt cathode, and Ti/RuO2 anode. The treated synthetic wastewater contains 100 mg L−1 of EB and has a pH = 3. The effects of three independent variables have been considered for process optimization, such as applied current intensity (0.1–0.5 A), iron concentration (1–10 mM), and stirring rate (100–1000 rpm). Their interactions were investigated considering response surface methodology (RSM) based on Doehlert design as optimization method. EB removal efficiency and energy consumption were considered as model responses after 30 min of electrolysis. Analysis of variance (ANOVA) revealed that the quadratic model was adequately fitted to the experimental data with R2 (0.9819), adj-R2 (0.9276), and low Fisher probability (< 0.0181) for the EB removal model, and R2 (0.9968), adj-R2 (0.9872) and low Fisher probability (< 0.0014) relative to the energy consumption model, suggesting a robust statistical significance. The energy consumption model significantly depends on current density, as expected. The foregoing results obtained by RSM led to the following optimal conditions for EB degradation: current intensity of 0.2 A, iron concentration of 9.397 mM, and stirring rate of 500 rpm, which gave a maximum decolorization rate of 98.15% with a minimum energy consumption of 0.74 kWh m−3 after 30 min of electrolysis. The competitiveness of the electro-Fenton process has been confirmed by the literature analysis proposed as well as by the preliminary economic analysis proposed in the second section of the study. Graphical abstract: (Figure presented.)
Electrochemical technologies for wastewater treatment at pilot plant scale
No full textProcess scale-up is a critical, but essential, step in the development of real electrochemical system for
oxidation of organic compound. This mini review wants critically analyze the research efforts carried out in the last years about pre-pilot and pilot scale plants, to support the implementation of such
technologies in industrial environmental. In the first section are presented the potentiality and the
issues related to the anodic oxidation. The second part is dedicated to the electro-Fenton process,
while the last is focused on the coupling of the two previous methods. The analysis highlights key
factors which are involved in the scaling-up, which are concerning not only the plant size, but
involved also their efficiency and economic feasibility
Coupling a Boron Doped Diamond Anode with a Solid Polymer Electrolyte to Avoid the Addition of Supporting Electrolyte in Electrochemical Advanced Oxidation Processes
No full textThe application of electrochemical technologies to wastewater treatment is limited by solution conductivity. In this paper, a solid polymer electrolyte Nafion® membrane has been used sandwiched between a boron doped diamond (BDD) anode and Ti/RuO2 cathode meshes to treat Bismarck Brown Y (BBY) solutions with very low conductivity. BBY has been chosen as model compound to the system, and the influence of several process parameters has been investigated. During the experiments the evolution of chemical oxygen demand (COD), color removal and nitrogen compounds have been monitored. The performances were strongly related with applied current and stirring rate, changed in a range of 0.5–2 A and 200 and 850 rpm, respectively. Their increment leads to a decrease of oxidation time required to remove BBY completely. The effect of the presence of Na2SO4 (2 and 7 mM) as supporting electrolyte has been also evaluated. Results were compared with a removal treatment carried out with a conventional batch system, using a flow cell containing liquid supporting electrolyte (Na2SO4). This comparison highlighted that the new cell setup is performing better in removing organic compounds, and thus, can be considered as effective process for the treatment of solutions with a low conductivity
Chlorpyrifos removal: Nb/boron-doped diamond anode coupled with solid polymer electrolyte and ultrasound irradiation
No full textChlorpyrifos is an organophosphorus insecticide, acaricide and miticide used worldwide for the control of soil-borne insect pests. It must be considered as a substance of growing concern, given its use, toxicity, environmental occurrence, and potential for regional to long-range atmospheric transport. Considering the incomplete removal attained by conventional water treatment processes, we investigated the efficiency of electrolytic radicals production and sonoelectrolysis on the degradation of the pesticide. The treatment has been conducted in a novel electrochemical reactor, equipped with a boron-doped diamond anode and a solid polymer electrolyte (SPE). Different current intensity and times have been tested and coupled with sonication at 40 kHz. Up to 69% of chlorpyrifos was completely removed in 10 min by electrolysis operated at 0.1 mA, while 12.5% and 5.4% was converted into the treatment intermediates 3,5,6-trichloro-2-pyridinol (TCP) and diethyl (3,5,6-trichloropyridin-2-yl) phosphate, respectively. Ultrasound irradiation did not enhance the removal efficiency, likely due to mass transport limitations, while the energy consumption increased from 8.68 center dot 10(- 6)to 9.34 center dot 10(- 4)kWh mu g(- 1)removed. Further research is encouraged, given the promising processing by the SPE technology of low conductivity solutions, as pharmaceuticals streams, as well as the potential for water and in-situ groundwater remediation from different emerging pollutants as phytosanitary and personal care products
Mathematical modeling of the anodic oxidation of organic pollutants: a review
No full textAnodic oxidation is a promising method for removing organic pollutants from water due to its high nonselectivity and effectiveness. Nevertheless, its widespread application is limited due to its low current efficiency, high energy consumption and low treatment rates. These problems may be overcome by the optimization of the process parameters, reactor design and electrode geometry, by coupling the experimental investigations with mathematical modeling. Here we review the modeling of anodic oxidation with focus on basics of this process, the competition phenomenon in real wastewater, flow cells and batch cells, historical aspects, general modeling equations, modeling with plate electrodes, modeling with porous 3-dimension electrodes and the density functional theory. Mathematical modeling can provide current, voltage and concentration distributions in the system. Mathematical modeling can also determine the effects on the performance of parameters such as diffusion layer thickness, flow velocity, applied current density, solution treatment time, initial concentration and diffusion coefficients of organic pollutants, electrode surface area, and oxidation reaction rate constant. Mathematical models allow to determine whether the limiting factor of the process is kinetics or diffusion, and to study the impact of competition of phenomena. The density functional theory provides information on probable reaction pathways and by-products
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