Carbon has long been one of the most investigated elements in the periodic table, par ticularly due to its versatility, which allows for the formation of structures with different dimensionalities and hybridizations. Unlike the well-known diamond and graphite, with sp3 and sp2 hybridizations respectively, there has been almost exclusively theoretical re search concerning the third allotropic form, consisting entirely of sp-carbon and known as carbyne. The promising properties theorized for this material, such as a high surface area, elevated electrical conductivity and mechanical properties, have justified the study of carbyne, despite its main limitation: high reactivity and a tendency to rearrange into more stable hybridized forms (i.e. sp2-hybridized structures). Today, it is possible to synthesize finite linear chains of sp-hybridized carbon, known as carbon atomic wires (CAWs). Depending on the chain length and terminal group type, CAWs exhibit differ ent vibrational properties, studied primarily through Raman spectroscopy, and tunable electronic conductivities. One promising application for this class of materials could be in the field of energy storage, as active materials for supercapacitor electrodes. Specifically, this thesis aims to examine the supercapacitive properties of a molecule belonging to the CAWs class, containing three double bonds in the chain and two phenyl groups as termi nations, tetraphenyl[3]cumulene or [3]Ph. Initially, a solution of [3]Ph and polymethyl methacrylate (PMMA) in N,N-dimethylformamide (DMF) was deposited via drop casting on carbon paper substrates. The polymer was used both as a binder, to facilitate the formation of a homogeneous film, and as a protective matrix to prevent cumulenes degra dation, as these are highly unstable by nature. The electrodes were then assembled using three different KOH concentrations (1M, 3M, and 6M) as electrolyte to determine the optimal performance. The cell with 3M concentration was found to yield the highest per formance (3.5 mF cm−2), providing both high ionic conductivity and adequate stability of the linear chains, as studied through Raman analysis of the characteristic sp-carbon peak. To address the poor reproducibility of results obtained from films deposited by drop casting, spray coating was explored as an alternative technique. After optimizing depo sition parameters, the repeatability of electrochemical results was demonstrated, though the main limitation of spray coating, the difficulty in achieving a high mass of deposited active material sufficient to contribute to system capacitance, was noted. Similarly, an electrode with [3]Ph-alone active material was prepared using both techniques, demon strating that spray coating is effective in obtaining well cohesive cumulenic crystals, which provide greater cyclic stability and better interface coupling with the substrate. Through Raman analysis, it was possible to verify the unexpected non-degradation of the material after electrochemical characterization. The solvent used in solution preparation plays a fundamental role in the deposition process; in particular, the boiling point and solubility of [3]Ph influence the number of layers required to create a sample with a loading mass on the order of milligrams. Dichloromethane (DCM) was selected as an alternative solvent to minimize deposition time and solution waste, as it has high solubilizing capacity for [3]Ph and a very low boiling point compared to DMF. However, films deposited in this way appeared powdery, with lower gravimetric capacitance and poorer crystalline qual ity. The study also analyzed the effects of carbon paper substrate activation to improve solvent wettability and the impact of post-deposition thermal treatment to enhance the overall capacitive properties of the electrodes. Finally, a brief comparative study with [5]Ph, a molecule differing from [3]Ph by the addition of one double bond in the chain, was conducted, revealing poorer performance. Although further studies are necessary to achieve a more comprehensive characterization, this thesis demonstrates that CAWs are excellent candidates in the field of energy storage, paving the way for future applications as supercapacitor electrodes.
Il carbonio è da sempre uno degli elementi più investigati della tavola periodica, so prattutto per la sua versatilità che permette la realizzazione di strutture con differenti dimensionalità e ibridizzazioni. A differenza dei conosciuti diamante e grafite, con ibridiz zazione rispettivamente sp3 e sp2, della terza forma allotropica, interamente formata da carboni sp, chiamata carbyne, sono presenti quasi unicamente studi teorici. Le promet tenti proprietà teorizzate per quest’ultimo materiale, quali un’estesa area superficiale ed elevata conducibilità elettrica nonché proprietà meccaniche, ne hanno giustificato lo stu dio; la principale limitazione resta la sua elevata reattività e tendenza a trasformarsi nelle forme di ibridizzazione più stabili, come strutture ibridizzate sp2. Oggi è possibile real izzare catene lineari di carbonio ibridizzato sp con dimensione finita, i cosiddetti CAWs. A seconda della lunghezza di catena e del tipo di gruppo di terminazione, i CAWs pre sentano diverse proprietà vibrazionali, identificabili soprattutto mediante spettroscopia Raman, e differente conducibilità elettronica. Un’interessante applicazione per questa classe di materiali potrebbe essere nell’ambito dello stoccaggio di energia, come materiale attivo per elettrodi di supercapacitori. Nello specifico questa tesi si propone di esaminare le proprietà supercapacitive di una molecola appartenente alla classe dei CAWs, con tre doppi legami in catena e due gruppi fenilici per terminazione, il tetrafenile[3]cumulene o [3]Ph. Inizialmente, una soluzione con base N,N-dimetilformammide (DMF) e contenente sia [3]Ph che polimetilmetacrilato (PMMA) è stata depositata mediante drop casting (de posizione per gocciolamento) su un substrato di carta di carbonio. Il polimero è stato impiegato sia come collante, per facilitare la realizzazione di un film omogeneo, sia per fungere da matrice protettiva ed evitare la degradazione dei cumuleni, essendo molto in stabili per natura. Gli elettrodi sono poi stati assemblati usando tre diverse concentrazioni di KOH, 1M, 3M e 6M, come elettrolita per verificare quale ottimizzasse la prestazione. La performance è stata massimizzata nella cella contenente la concentrazione 3M (3.5 mF cm−2), che è in grado di garantire al contempo alta conducibilità ionica e sufficiente stabilità delle catene lineari, studiata mediante analisi Raman del picco caratteristico del carbonio sp. Per rimediare alla scarsa riproducibilità dei risultati ottenuta dai film deposi tati con drop casting, lo spray coating è stato esplorato come tecnica alternativa. Dopo aver ottimizzato i parametri della deposizione, la ripetibilità dei risultati elettrochimici è stata dimostrata, evidenziando, però, il principale limite dello spray coating, ovvero la difficoltà nell’ottenere un’elevata massa di materiale attivo depositato che dia sufficiente contributo alla capacità del sistema. Similmente un elettrodo il cui materiale attivo è solo il [3]Ph, è stato preparato con le due diverse tecniche, mostrando come lo spray coating sia efficace nell’ottenere cristalli cumulenici ben coesi che diano maggiore stabilità ciclica e miglior accoppiamento all’interfaccia con il substrato. Attraverso l’analisi Raman è stato possibile verificare l’inaspettata non degradazione del materiale dopo la caratterizzazione elettrochimica. Il solvente impiegato nella preparazione della soluzione ha un ruolo fonda mentale durante la deposizione, in modo particolare il punto di ebollizione e la solubilità del [3]Ph influenzano il numero di passate necessarie per la realizzazione di un layer di massa dell’ordine dei milligrammi. Il diclorometano è stato scelto come solvente alterna tivo per minimizzare i tempi di deposizione e lo spreco di soluzione, presentando elevata capacità di solubilizzare il [3]Ph e un punto di ebollizione molto basso, contrariamente al DMF. I film depositati in questo modo risultano, tuttavia, polverosi, con conseguenti val ori inferiori di capacità gravimetrica e peggior qualità cristallina. Nello studio sono anche analizzati gli effetti dell’attivazione del substrato di carta di carbonio, volto a migliorare la bagnabilità per il solvente, e l’effetto del trattamento termico dopo la deposizione per il miglioramento delle proprietà capacitive complessive degli elettrodi. Infine, un breve studio comparativo con il [5]Ph, molecola che differisce dal [3]Ph per l’aggiunta di un doppio legame in catena, è stato realizzato, riportando performance peggiori nel caso del [5]Ph. Nonostante ulteriori studi siano necessari per avere una caratterizzazione più completa, attraverso questa tesi è stato possibile dimostrare come i CAWs siano degli ottimi candi dati per applicazioni nello stoccaggio di energia, aprendo la strada a future applicazioni come elettrodi per supercapacitori.
Exploring the supercapacitive performances of size and termination-selected cumulenic sp-carbon wires
Tosi Celli, Rachele
2023/2024
Abstract
Carbon has long been one of the most investigated elements in the periodic table, par ticularly due to its versatility, which allows for the formation of structures with different dimensionalities and hybridizations. Unlike the well-known diamond and graphite, with sp3 and sp2 hybridizations respectively, there has been almost exclusively theoretical re search concerning the third allotropic form, consisting entirely of sp-carbon and known as carbyne. The promising properties theorized for this material, such as a high surface area, elevated electrical conductivity and mechanical properties, have justified the study of carbyne, despite its main limitation: high reactivity and a tendency to rearrange into more stable hybridized forms (i.e. sp2-hybridized structures). Today, it is possible to synthesize finite linear chains of sp-hybridized carbon, known as carbon atomic wires (CAWs). Depending on the chain length and terminal group type, CAWs exhibit differ ent vibrational properties, studied primarily through Raman spectroscopy, and tunable electronic conductivities. One promising application for this class of materials could be in the field of energy storage, as active materials for supercapacitor electrodes. Specifically, this thesis aims to examine the supercapacitive properties of a molecule belonging to the CAWs class, containing three double bonds in the chain and two phenyl groups as termi nations, tetraphenyl[3]cumulene or [3]Ph. Initially, a solution of [3]Ph and polymethyl methacrylate (PMMA) in N,N-dimethylformamide (DMF) was deposited via drop casting on carbon paper substrates. The polymer was used both as a binder, to facilitate the formation of a homogeneous film, and as a protective matrix to prevent cumulenes degra dation, as these are highly unstable by nature. The electrodes were then assembled using three different KOH concentrations (1M, 3M, and 6M) as electrolyte to determine the optimal performance. The cell with 3M concentration was found to yield the highest per formance (3.5 mF cm−2), providing both high ionic conductivity and adequate stability of the linear chains, as studied through Raman analysis of the characteristic sp-carbon peak. To address the poor reproducibility of results obtained from films deposited by drop casting, spray coating was explored as an alternative technique. After optimizing depo sition parameters, the repeatability of electrochemical results was demonstrated, though the main limitation of spray coating, the difficulty in achieving a high mass of deposited active material sufficient to contribute to system capacitance, was noted. Similarly, an electrode with [3]Ph-alone active material was prepared using both techniques, demon strating that spray coating is effective in obtaining well cohesive cumulenic crystals, which provide greater cyclic stability and better interface coupling with the substrate. Through Raman analysis, it was possible to verify the unexpected non-degradation of the material after electrochemical characterization. The solvent used in solution preparation plays a fundamental role in the deposition process; in particular, the boiling point and solubility of [3]Ph influence the number of layers required to create a sample with a loading mass on the order of milligrams. Dichloromethane (DCM) was selected as an alternative solvent to minimize deposition time and solution waste, as it has high solubilizing capacity for [3]Ph and a very low boiling point compared to DMF. However, films deposited in this way appeared powdery, with lower gravimetric capacitance and poorer crystalline qual ity. The study also analyzed the effects of carbon paper substrate activation to improve solvent wettability and the impact of post-deposition thermal treatment to enhance the overall capacitive properties of the electrodes. Finally, a brief comparative study with [5]Ph, a molecule differing from [3]Ph by the addition of one double bond in the chain, was conducted, revealing poorer performance. Although further studies are necessary to achieve a more comprehensive characterization, this thesis demonstrates that CAWs are excellent candidates in the field of energy storage, paving the way for future applications as supercapacitor electrodes.File | Dimensione | Formato | |
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2024_12_Tosi_Celli_Executive_Summary.pdf
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2024_12_Tosi_Celli_Tesi.pdf
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https://hdl.handle.net/10589/230947