Cathodes for zinc-air batteries

Μεχίλη, Μαρία; Mechili, Maria

dc.contributor.author	Μεχίλη, Μαρία	el
dc.contributor.author	Mechili, Maria	en
dc.date.accessioned	2021-09-24T11:53:52Z
dc.date.available	2021-09-24T11:53:52Z
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/53892
dc.identifier.uri	http://dx.doi.org/10.26240/heal.ntua.21590
dc.rights	Default License
dc.subject	Zinc-Air Battery	el
dc.subject	Cathode	en
dc.subject	Gas-Diffusion electrode	en
dc.subject	Electrocatalyst	en
dc.subject	Perovskite	en
dc.title	Cathodes for zinc-air batteries	el
heal.type	bachelorThesis
heal.classification	Energy Applied Materials, Materials, Electrochemistry	el
heal.language	en
heal.access	free
heal.recordProvider	ntua	el
heal.publicationDate	2021-07-05
heal.abstract	Zinc-air batteries (ZABs) are rising contenders for future applications in power sources and storage sectors, due to their intrinsically elevated energy capacity coexisting with eco-friendly characteristics. Although rechargeable aqueous ZABs hold a considerable position in current research reports, their practical large-scale adoption is still obstructed by poor durability and cyclability. The bifunctional electrocatalyst in the cathode appears to be the controlling factor of the efficiency of the zinc-air cell, thus special effort has been invested into discovering effective and low-cost alternatives. Transition metal oxides have invariably been considered as competent ORR and OER electrocatalysts for other energy applications, while perovskites have been recently explored as lower cost candidates. The scope of the present thesis is to investigate the performance of layered perovskites PrBaCo2O6-δ (PBC) and PrBaCo1.4Fe0.6O6-δ (PBCF) when implemented as cathode materials in a laboratory secondary aqueous Zinc Air Cell. Before moving to the experimental procedure, a theoretical background of the subject is outlined. Firstly, the fundamental operational aspects of zinc air batteries (ZABs) are defined. ZABs function differently from conventional batteries, as the oxidizing material is oxygen from the environment, that enters through the cathode (gas-diffusion electrode) to the system, allowing the battery to possess essentially reduced weight. Then, the principal limitations and recent research advances of each component of ZABs are discussed. It appears that ZABs constitute a complex system whose operation can be restricted by various sources, such as anode passivation and parasitic reactions. Nevertheless, the gas-diffusion electrode remains the most delicate part of ZABs, thus recently a remarkable number of reports are devoted into figuring out efficient and scalable solutions for ZABS cathode materials. The major demand from cathode materials is the simultaneous catalysis of Oxygen Reduction Reaction (ORR) and Oxygen Evolution Reaction (OER) in alkaline media and a resilience throughout consistent cycling of the battery. Considering the continuous recent research for bifunctional electrocatalysts, a brief overview of perovskites applied lately as air electrodes is provided. In order to evaluate the performance of PBC and PBCF, electrochemical characterization half-cell and full-cell tests were conducted. Half-cell tests were devoted to the verification of electrocatalytic activity of the perovskites, in a three-electrode configuration, via voltammetry techniques. After the catalysis of ORR and OER was confirmed, Linear Sweep Voltammetry was used to estimate OER kinetic parameters, so an overall comparison of the activity of the two perovskites could be derived. Tafel slope was conceived as the main activity descriptor for OER dynamics Finally, PBC and PBCF catalyst inks were coated on carbon paper (gas diffusion layer) to form cathode electrodes which were applied in a in situ assembled ZAB. Each ZAB was tested as a primary battery system and afterwards towards its rechargeability in the same test protocol and conditions, in order to obtain comparable results for the two catalysts. After measuring the Open Circuit Voltage (OCV) of ZABs, Galvanodynamic Polarization curves were acquired, so as to inspect voltage losses during applied currents. Peak Power Densities were also calculated for each catalyst. Taking into consideration the data from the current scan of the cell, a current density was chosen to conduct a galvanostatic full discharge of each cell for Battery Capacity and Working Voltage determination. Following the primary battery tests, a charge voltage profile was obtained, through galvanostatic charging of the battery and polarization towards OER was inspected. Lastly, the ZABs were submitted to continuous galvanostatic charge-discharge cycling to observe voltage polarizations and test the durability of catalysts. Both electrochemical half-cell tests and battery tests revealed enhanced performance of Fe-doped PBC comparing to pristine PBC. Tafel slopes of PBCF samples were overall reduced compared to PBC, implying better OER activity of PBCF which was confirmed by following battery tests. Although both catalysts delivered relatively low Specific Capacity, the Peak Powe Density derived from Polarization plots illustrate the potential of the two catalysts to facilitate ORR. During galvanostatic cycling PBCF appears more efficient than PBC it exhibited less extended Voltage Gap throughout its cycle life. It is highlighted that PBCF could attain 130 (20min) cycles at 2.3-3 mAcm-2 without exceeding the charging voltage of 2V, verifying the successful limitation of overpotentials during OER, compared to recent reports of catalysts applied in ZABs. Despite the fact that no direct comparison of the two catalysts can be driven, due to lack of morphology, porosity and real surface area information, the improved performance of PBCF could be partially attributed to B-site doping of PBC.	el
heal.advisorName	Αργυρούσης, Χρήστος	el
heal.committeeMemberName	Καραντώνης , Αντώνης	el
heal.academicPublisher	Εθνικό Μετσόβιο Πολυτεχνείο. Σχολή Χημικών Μηχανικών. Τομέας Σύνθεσης και Ανάπτυξης Βιομηχανικών Διαδικασιών (IV). Εργαστήριο Τεχνολογίας Ανόργανων Υλικών	el
heal.academicPublisherID	ntua
heal.numberOfPages	97 σ.	el
heal.fullTextAvailability	false