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Development of High-performance Bi-functional Oxygen Electrocatalysts for Rechargeable Zn-air Batteries.

Wu, Mingjie (2021). Development of High-performance Bi-functional Oxygen Electrocatalysts for Rechargeable Zn-air Batteries. Thèse. Québec, Doctorat en sciences de l'énergie et des matériaux, Université du Québec, Institut national de la recherche scientifique, 194 p.

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Résumé

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Rechargeable zinc-air batteries (ZABs) are considered one of the most promising candidates as power sources for portable electronic devices, electric vehicles (EVs), and grid storage, due to their high energy density (1218 Wh kg-1 ), environmentally benignity, safe operational characteristics, and low production cost. One of the biggest challenges and the bottleneck in developing high-performance rechargeable ZABs is the design of suitable bifunctional air electrodes, with controlled chemical compositions and well-designed architectures that can efficiently catalyze the key oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Air electrodes with bifunctional catalytic activity (ORR and OER) are the most significant and complicated part of the rechargeable ZABs that inevitably determine the electrochemical performance and cycling stability. This thesis describes facile synthetic strategies for the fabrication of bifunctional oxygen electrodes for rechargeable ZABs. In the first study, we developed a facile method to fabricate graphitic-shell encapsulated binary FeNi alloy/nitride nanocrystals and biomass-derived N-doped carbon (NC) hybrid (FexNiyN@C/NC) structures. The porous architecture can provide abundant accessible active sites and improved mass transfer. Benefitting from the high graphitization of the carbon layer and strong metal-support interactions between the graphite-coated FexNiyN nanocrystals and the N doped porous carbon, the hybrid material (FexNiyN@C/NC) can take full advantage of the unique structures to promote the electrocatalytic reaction kinetics and stability for both ORR and OER. As expected, the obtained FexNiyN@C/NC catalyst exhibits high bifunctional ORR/OER activity, indicated by the small potential gap (ΔE) of 0.67 V between Ej = 10 (1.54 V) and E1/2 (0.87 V) in 1.0 M KOH. The electrochemical tests and X-ray absorption spectroscopy (XAS) analyses revealed that there is almost no change in the bulk structure of the FexNiyN nanocrystals after suffering the harsh OER electrochemical corrosion process. When integrated into an air electrode for the rechargeable ZAB, the hybrid catalyst demonstrated high stability over 400 hours at 5.0 mA cm-2 . To further improve the graphitization extents of carbon and reduce the part of the amorphous carbon, a facile two-step strategy has been developed to synthesize diphasic metal/metal phosphide nanoparticles encapsulated in the bamboo-shape N-doped CNTs (M/M2P@NCNTs). Among them, the unique heterojunction structure of the Co/Co2P greatly induces the construction of highly ordered NCNTs with rich pyridinic-N and graphitic-N active sites. This straightforward strategy is a valid measure to avoid the destruction of ORR active sites due to the high potential oxidation conditions. Typically, the Co/Co2P@NCNTs (E1/2=0.90 V) has exhibited outstanding ORR performance with an E1/2 of 0.87 V versus RHE after suffering high potential oxidation condition, which to the best of our knowledge, is record-level among previously reported ORR catalysts. Meanwhile, deep self-reconstruction of heterojunction Co/Co2P confined in NCNTs shows increasing OER performance owing to the dynamic active state generation of plentiful CoOx(OH)y active species. This is different from the previously reported structural transformation that occurred only in the near-surface region of cobalt oxides. Benefiting from the high oxidation potentials resistance of the NCNT and the transformation from the heterojunction Co/Co2P into Co3+ containing CoOx(OH)y active species, the Co/Co2P@NCNTs can be used as an efficient bifunctional precatalyst for rechargeable zinc-air flow batteries. The assembled zinc-air flow battery with the developed catalyst displays high cell efficiency with an unprecedented cycle life of 1000 h in an ambient environment, indicating the promising application of these catalysts in metal-air batteries. Further, a facile bimetal coupling approach was used to synthesize Fe/Co double hydroxide/oxide nano-sheets cladding layer on N-doped multiwall carbon nanotubes (FeCo- DHO/NCNTs). Through the direct nucleation, growth, and anchoring, the Fe/Co double hydroxide/oxide nano-sheets (FeCo-DHO) with crystalline and amorphous phases are uniformly inlaid on the surface of NCNTs, which provide high electrical contact area and strong adhesion on the conductive carbon support. The strong interactions of the FeCo-DHO nano-sheets with NCNTs (possibly due to the formation of M-O-C (M = Co, Fe) chemical bonding) not only greatly facilitate the charge transfer and mass transport but also lead to high chemical stability to resist the corrosion during charge and discharge operation. Consequently, the as-synthesized FeCo-DHO/NCNTs exhibits high bifunctional ORR/OER activity and stability, with a potential gap of 0.7 V between Ej=10 (OER, potential at 10.0 mA cm-2 ) and E1/2 (ORR, half-wave potential). In addition, outstanding charging-discharging performance and long cycling lifetime were achieved in liquid and quasi-solid-state ZABs. The high electrochemical performance of such catalysts thereby makes it very promising to replace the noble-metal catalysts (Pt group metals for ORR and Ir/Ru group metals for OER) in metal-air batteries. Finally, a self-supported electrode as a high-performance binder- and carbon-free cathode for rechargeable hybrid zinc batteries are explored. In this work, The Ni foam (NF) in this work not only acts as a substrate but also serves as a nickel precursor for the formation of the Co3-xNixO4 catalyst. Meanwhile, combining the 3D porous structure of NF and intrinsic high OER activity of the stainless steel (SS), the assembled porous air electrode can take full advantage of the sandwich structure to promote the electrocatalytic reaction kinetics. This novel nanostructure demonstrates a very high reversible Faradaic redox reaction of CoNi-O ↔ CoNi-O-OH and high bifunctional activity toward both ORR and OER. Moreover, the air cathode, prepared by pressing the stainless steel SS@Co3O4 sandwiched between two NF@Co3-xNixO4, possesses a dense and interconnected structure with a high loading of active catalyst. The rechargeable hybrid battery system, assembled from this NS@Co3-xNixO4/Co3O4 electrode based on both Zn-Co3-xNixO4 and Zn-air electrochemical reactions, exhibits much higher energy efficiency and durability than those of commercial Pt/C and RuO2 electrocatalysts. This protocol opens a new avenue for the rational design of highly efficient and stable self-supported air electrodes for metal-air batteries.

Type de document: Thèse Thèse
Directeur de mémoire/thèse: Sun, Shuhui
Mots-clés libres: rechargeable zinc-air battery; hybrid zinc batteries; bifunctional electrocatalysts; defects; FeNi alloy/nitrides; heterojunction structure; self-supported; degree of graphitization
Centre: Centre Énergie Matériaux Télécommunications
Date de dépôt: 19 nov. 2021 14:43
Dernière modification: 25 nov. 2021 19:20
URI: https://espace.inrs.ca/id/eprint/12076

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