In recent years, manganese oxides (MnOx) in their various forms, including Mn2O3, Mn3O4 and MnO2 polymorphs, have been extensively investigated as cathode materials for energy storage and conversion applications. They possess several advantages, including abundant reserves, low cost and toxicity, good capacity, and capacitance. Among various applications, Mn oxides have gained significant attention as promising cathode materials for aqueous zinc-ion batteries. However, MnOx exhibits complex and varied electrochemistry, which is influenced by both the properties of MnOx (structure/phase and morphology at the nanoscale) and the electrolytic environment. This thesis has focused on monitoring the structural or phase changes of different MnOx thin films with specific phases and morphologies induced by electrochemical polarization by means of in situ Raman spectroscopy in operando conditions. Additionally, this thesis focused on the evaluation of the phase transformations of layered MnO2 upon the insertion of selected metal ions during annealing by means of ex situ Raman spectroscopy. The MnOx thin films were produced by pulsed laser deposition in different atmospheres and post-deposition thermal annealing. In order to achieve these goals, in addition to Raman spectroscopy, SEM and EDX techniques were used. The electrochemical in situ Raman spectroscopy setup was constructed and optimized and subsequently used to monitor the structural changes occurring at the working electrode while the potential was applied. The in situ investigation revealed that the morphology strongly affects the electrochemical response: the porous MnOx films structurally modified to a more oxidized phase or to a more crystalline framework upon anodic polarization, while the compact ones remained unchanged in their original structure, up to the anodic formation of Mn(VII) or cathodic dissolution to Mn(II). On the other hand, the solid-state diffusion of metal ions revealed that Na+ and K+ ions stabilize the α-MnO2 and the layered K-MnO2 phases, respectively, while Zn2+ ions stabilize the ZnMn2O4 phase.
Negli ultimi anni, gli ossidi di manganese (MnOx) nelle loro varie forme (Mn2O3, Mn3O4 e i polimorfi di MnO2) sono stati ampiamente studiati come materiali catodici per l'accumulo e la conversione di energia. Possiedono diversi vantaggi, tra cui abbondanza di riserve, basso costo e tossicità, buona capacità e capacitanza. Tra le varie applicazioni, gli ossidi di Mn hanno suscitato grande interesse come materiali catodici per le batterie acquose allo zinco. Tuttavia, l'ossido di Mn presenta un'elettrochimica complessa e diversificata, influenzata sia dalle proprietà del MnOx (struttura/fase e morfologia su scala nanometrica) che dall'ambiente elettrolitico. Questa tesi si è concentrata sul monitoraggio dei cambiamenti strutturali (e di fase) dei film sottili di MnOx (con specifiche fasi e morfologie) indotte sia dalla polarizzazione elettrochimica che dall’inserimento di specifici ioni metallici all'interno del film stratificato di MnO2 durante trattamenti termici, utilizzando la spettroscopia Raman. I film sottili di MnOx con diversa fase e morfologia alla nanoscala sono stati ottenuti tramite la tecnica di deposizione laser pulsata e trattamenti termici di post-deposizione in atmosfera controllata. Al fine di raggiungere questi obiettivi, oltre alla spettroscopia Raman, sono state utilizzate le tecniche SEM e EDX. In particolare, per il primo obbiettivo è stato messo a punto il setup per la spettroscopia Raman in situ combinata con l'elettrochimica che ha permesso di monitorare i cambiamenti strutturali al catodo durante l'elettrochimica. L'indagine in situ ha rivelato che la morfologia influenza fortemente la risposta elettrochimica: i film porosi di MnOx si modificano strutturalmente in una fase più ossidata o in una struttura più cristallina quando sottoposti ad una polarizzazione anodica, mentre quelli compatti rimangono invariati nella loro struttura originale, fino alla formazione anodica di Mn(VII) o alla dissoluzione catodica a Mn(II). Mentre, la diffusione allo stato solido ha mostrato che gli ioni Na+ e K+ stabilizzano la fase α-MnO2 e le fase stratificata K-MnO2, rispettivamente, mentre lo ione Zn2+ stabilizza la fase ZnMn2O4.
Raman investigation of structural modifications of manganese oxide thin films
Hallqvist, Claudia Pernilla
2022/2023
Abstract
In recent years, manganese oxides (MnOx) in their various forms, including Mn2O3, Mn3O4 and MnO2 polymorphs, have been extensively investigated as cathode materials for energy storage and conversion applications. They possess several advantages, including abundant reserves, low cost and toxicity, good capacity, and capacitance. Among various applications, Mn oxides have gained significant attention as promising cathode materials for aqueous zinc-ion batteries. However, MnOx exhibits complex and varied electrochemistry, which is influenced by both the properties of MnOx (structure/phase and morphology at the nanoscale) and the electrolytic environment. This thesis has focused on monitoring the structural or phase changes of different MnOx thin films with specific phases and morphologies induced by electrochemical polarization by means of in situ Raman spectroscopy in operando conditions. Additionally, this thesis focused on the evaluation of the phase transformations of layered MnO2 upon the insertion of selected metal ions during annealing by means of ex situ Raman spectroscopy. The MnOx thin films were produced by pulsed laser deposition in different atmospheres and post-deposition thermal annealing. In order to achieve these goals, in addition to Raman spectroscopy, SEM and EDX techniques were used. The electrochemical in situ Raman spectroscopy setup was constructed and optimized and subsequently used to monitor the structural changes occurring at the working electrode while the potential was applied. The in situ investigation revealed that the morphology strongly affects the electrochemical response: the porous MnOx films structurally modified to a more oxidized phase or to a more crystalline framework upon anodic polarization, while the compact ones remained unchanged in their original structure, up to the anodic formation of Mn(VII) or cathodic dissolution to Mn(II). On the other hand, the solid-state diffusion of metal ions revealed that Na+ and K+ ions stabilize the α-MnO2 and the layered K-MnO2 phases, respectively, while Zn2+ ions stabilize the ZnMn2O4 phase.File | Dimensione | Formato | |
---|---|---|---|
2023_07_Hallqvist_Tesi_01.pdf
Open Access dal 27/06/2024
Descrizione: testo tesi
Dimensione
82.55 MB
Formato
Adobe PDF
|
82.55 MB | Adobe PDF | Visualizza/Apri |
2023_07_Hallqvist_Executive Summary_02.pdf
Open Access dal 27/06/2024
Descrizione: Executive Summary
Dimensione
14.54 MB
Formato
Adobe PDF
|
14.54 MB | Adobe PDF | Visualizza/Apri |
I documenti in POLITesi sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
https://hdl.handle.net/10589/208043