Energy storage devices play an undeniable role in developments of renewable sources exploitation, and without this support, the scenario of making renewables prominent means of energy would collapse right away. With the advances in redox flow battery technology, these systems have become reliable tools for large-scale applications to be used for this purpose. Independent stored energy and power, and efficient operation are couple of those factors making this technology so precious. VRFB are recognized as one of the most domineering devices of this group with long life-time, and minimized malfunctions of crossover phenomena. Some missing points as lack of economic feasibilities, and lower power densities with respect to similar approaches demand them for further improvements. The present work would deal with many aspects of VRFB application to improve its operation. In this regard, some structural modifications with various setups have been considered to enhance the cell performance. Different diagnostic approaches and measurements have been considered for better understanding of system behavior. After observing improvements of global performance with analyzing different arrangements of blockages over graphite plates, it is aimed to validate this innovative approach compared to conventional choices. Flow field is regarded as very important component in cell assembly in identifying entire response of the battery, therefore, a meticulous optimization should be conducted in design stage. Two types of electrodes with different thickness were considered alongside novel geometry characterizations. With observed advances of different hybrid combinations of the obstacles, the great focus of this thesis is placed on function of modified plates. These novel plates are obtained through investigating the interplay of fluid dynamic of flow in channels and reagents interactions with porous electrodes to cut the overpotentials. Intensified under the rib fluxes with localized pressure drops and accelerated downstream flow benefited the innovative network in terms of electrochemical performance with the cost of slight pressure drops. Enhanced performance of locally modified flow fields was supported by polarization studies of different setups and considering both half-cells. It was displayed that mass transport issues are significantly addressed at higher current densities, with uniform delivery and distribution of reactants over active area. Moreover, decent cycle life was provided by this design scheme that was analyzed through various parameters. The lowest capacity fading rate, and highest energy efficiency alongside the least aging issues and affection after performed cycles were captured with innovative plates. Adoption of segmented cell to observe local operation, resulted in maintenance of enhanced cycle life of modified geometry also at local scale. The promising behavior of this geometry would pave the gaps for obtaining enhanced performances, if the validity and superior behavior could be observed employing different redox couples.
I dispositivi di accumulo di energia svolgono un ruolo innegabile negli sviluppi dello sfruttamento delle fonti rinnovabili e senza questo supporto lo scenario di rendere le energie rinnovabili un’importante fonte di energia collasserebbe immediatamente. Con i progressi della tecnologia delle batterie a flusso redox, questi sistemi sono diventati strumenti affidabili per applicazioni su larga scala da utilizzare per questo scopo. Energia e potenza immagazzinate indipendenti insieme al funzionamento efficiente sono fattori che rendono questa tecnologia così importante. I VRFB sono riconosciuti come uno dei dispositivi più importanti di questo settore con una lunga durata e malfunzionamenti minimizzati derivanti dai fenomeni crossover. Alcuni punti mancanti come mancanza di fattibilità economica e densità di potenza inferiori rispetto ad approcci simili richiedono loro ulteriori miglioramenti sulle aree citate. Il presente lavoro affronterebbe molti aspetti dell'applicazione VRFB per migliorarne il funzionamento. A questo proposito, sono state prese in considerazione alcune modifiche strutturali con varie configurazioni per migliorare le prestazioni della cella. Sono stati considerati diversi approcci diagnostici e misurazioni per una migliore comprensione del comportamento del sistema. Dopo aver osservato miglioramenti delle prestazioni globali con l'analisi delle diverse disposizioni di blocchi su lastre di grafite, si mira a convalidare questo approccio innovativo rispetto alle scelte convenzionali. Il flow field è considerato un componente molto importante nell'assemblaggio delle celle nell'identificazione dell'intera risposta della batteria, pertanto è necessario condurre una meticolosa ottimizzazione in fase di progettazione. Due tipi di elettrodi con diverso spessore sono stati considerati accanto a nuove caratterizzazioni geometriche. Con i progressi osservati delle diverse combinazioni ibride degli ostacoli, il grande focus di questa tesi è posto sulla funzione delle piastre modificate. Queste nuove piastre sono ottenute studiando l'interazione della fluidodinamica del flusso nei canali e le interazioni dei reagenti con gli elettrodi porosi per ridurre i sovrapotenziali. Intensificato sotto i rib fluxes con cadute di pressione localizzate e flusso a valle accelerato ha beneficiato della rete innovativa in termini di prestazioni elettrochimiche con il costo di lievi cadute di pressione. Le prestazioni migliorate dei campi di flusso modificati localmente sono state supportate da studi di polarizzazione di diverse configurazioni e considerando entrambe le semicelle. È stato dimostrato che i problemi di trasporto di massa vengono affrontati in modo significativo a densità di corrente più elevate, con consegna e distribuzione uniforme dei reagenti sull'area attiva. Inoltre, questo schema di progettazione ha fornito una durata del ciclo accettabile che è stata analizzata attraverso vari parametri. Il fading rate della capacità più bassa e la massima efficienza energetica insieme ai problemi di invecchiamento ed effetti dopo un numero di cicli eseguiti sono stati catturati con lastre innovative. L'adozione della cella segmentata ha permesso di osservare le operazioni locali e in seguito cicli di vita migliori per la geometria modificata sono stati mantenuti sus cala locale. Il comportamento promettente di questa geometria spianerebbe le lacune per ottenere prestazioni migliori, se la validità e il comportamento superiore potessero essere osservati impiegando diverse coppie redox.
Experimental characterization of improved flow fields in vanadium redox flow battery : insight into local performance evolution
FAKHIMI BONAB, MOHAMMAD
2019/2020
Abstract
Energy storage devices play an undeniable role in developments of renewable sources exploitation, and without this support, the scenario of making renewables prominent means of energy would collapse right away. With the advances in redox flow battery technology, these systems have become reliable tools for large-scale applications to be used for this purpose. Independent stored energy and power, and efficient operation are couple of those factors making this technology so precious. VRFB are recognized as one of the most domineering devices of this group with long life-time, and minimized malfunctions of crossover phenomena. Some missing points as lack of economic feasibilities, and lower power densities with respect to similar approaches demand them for further improvements. The present work would deal with many aspects of VRFB application to improve its operation. In this regard, some structural modifications with various setups have been considered to enhance the cell performance. Different diagnostic approaches and measurements have been considered for better understanding of system behavior. After observing improvements of global performance with analyzing different arrangements of blockages over graphite plates, it is aimed to validate this innovative approach compared to conventional choices. Flow field is regarded as very important component in cell assembly in identifying entire response of the battery, therefore, a meticulous optimization should be conducted in design stage. Two types of electrodes with different thickness were considered alongside novel geometry characterizations. With observed advances of different hybrid combinations of the obstacles, the great focus of this thesis is placed on function of modified plates. These novel plates are obtained through investigating the interplay of fluid dynamic of flow in channels and reagents interactions with porous electrodes to cut the overpotentials. Intensified under the rib fluxes with localized pressure drops and accelerated downstream flow benefited the innovative network in terms of electrochemical performance with the cost of slight pressure drops. Enhanced performance of locally modified flow fields was supported by polarization studies of different setups and considering both half-cells. It was displayed that mass transport issues are significantly addressed at higher current densities, with uniform delivery and distribution of reactants over active area. Moreover, decent cycle life was provided by this design scheme that was analyzed through various parameters. The lowest capacity fading rate, and highest energy efficiency alongside the least aging issues and affection after performed cycles were captured with innovative plates. Adoption of segmented cell to observe local operation, resulted in maintenance of enhanced cycle life of modified geometry also at local scale. The promising behavior of this geometry would pave the gaps for obtaining enhanced performances, if the validity and superior behavior could be observed employing different redox couples.| File | Dimensione | Formato | |
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Mohammad Fakhimi Bonab 896284 Master Thesis Revised Version.pdf
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https://hdl.handle.net/10589/167368