In recent years, two-dimensional (2D) materials have been widely studied for their peculiar properties which could lead to severe technological advancements. Wet-jet milling (WJM), a liquid-phase (LPE) exfoliation technique, was employed to produce graphene and 2D MoS2 flakes. In this Thesis work, I used graphene for supercapacitors (SCs) electrode slurries formulation and 2D MoS2 for proton-exchange membrane electrolyzers (PEMELs) cathode catalysts production. A H2-based thermal treatment was designed to further improve the performances of these devices, exploiting the beneficial properties given by the implementation of these materials. Supercapacitors are electrochemical energy storage devices operating at high power densities, but limited energy densities. The exploitation of graphene as electrode material has demonstrated to supply higher gravimetric capacitance (Cg), power density and rate capability to electric double layer capacitors (EDLCs). As these perks are provided by the 2D graphitic structure of graphene, the H2 thermal treatments aimed at producing a graphitization extended to the whole surface of the SCs active material. The sp2 bonds promotion and surface functionalities removal resulted in the 700 °C-treated electrodes-based EDLCs to report Cg and energy density gains of +39.4 % and +38.4 % at 1 A g-1, respectively, compared to the untreated electrodes-based EDLCs. Proton-exchange membrane electrolyzers are electrochemical energy conversion devices used for the hydrogen evolution reaction (HER). The catalytic activity reported by the Mo edge sites of 2D MoS2 could be stretched further throughout promotion of S vacancies via H2S evolution. The three-electrode cell electrochemical characterization revealed overpotential reductions by 26.7 % at -50 mA cm-2 for the 900 °C-treated 2D MoS2 catalysts compared to the untreated ones. Although laying still far (in terms of HER overpotentials) from commercially available Pt-based catalysts, the 900 °C-treated 2D MoS2-based PEMELs confirmed the reduction in cell voltage compared to the untreated 2D MoS2-based PEMELs. These results envisage open room for research on sustainable noble metals-free catalysts.
Negli ultimi anni, i materiali bidimensionali (2D) sono stati ampiamente studiati poiché potrebbero portare a numerosi progressi tecnologici. La fresatura a getto umido (WJM), una tecnica di esfoliazione in fase liquida, è stata impiegata per produrre grafene e 2D MoS2. In questo lavoro di Tesi ho utilizzato il grafene per formulare elettrodi per supercondensatori (SC) e il 2D MoS2 per produrre catalizzatori catodici per elettrolizzatori a membrana a scambio protonico (PEMEL). Per migliorare ulteriormente le prestazioni di questi dispositivi è stato progettato un trattamento termico a base di H2. I SC sono dispositivi elettrochimici per l’accumulo di energia che operano ad alte densità di potenza, ma basse densità di energia. Nei condensatori a doppio strato elettrico (EDLC), il grafene migliora capacità gravimetrica (Cg), densità di potenza e rate capability. Poiché questi vantaggi sono forniti dalla struttura grafitica 2D del grafene, i trattamenti termici in H2 avevano l’obiettivo di produrre una grafitizzazione superficiale dei materiali attivi. Grazie alla promozione di legami sp2 e alla rimozione di funzionalità superficiali, gli EDLC a base di elettrodi trattati a 700 °C hanno riportato aumenti di Cg e densità energetica rispettivamente del +39,4 % e del +38,4 % a 1 A g-1, rispetto agli EDLC basati su elettrodi non trattati. I PEMEL sono dispositivi elettrochimici per la conversione di energia in grado di evolvere idrogeno (HER). L'attività catalitica dei siti metallici nel 2D MoS2 può essere estesa rimuovendo S tramite l'evoluzione di H2S. La caratterizzazione elettrochimica delle celle a tre elettrodi ha rivelato riduzioni della sovratensione del 26.7 % a -50 mA cm-2 per gli elettrodi a base di 2D MoS2 trattati a 900 °C rispetto a quelli non trattati. Sebbene ancora lontani (in termini di sovratensione per la HER) dai catalizzatori a base di Pt disponibili in commercio, anche i PEMEL a base di 2D MoS2 trattato a 900 °C hanno convalidato la riduzione della tensione di cella rispetto ai PEMEL a base di 2D MoS2 non trattato. Questi risultati prospettano ampio spazio per la ricerca sui catalizzatori sostenibili privi di metalli nobili.
Hydrogen treated graphene-based and 2D MoS2-based electrochemical devices for energy harvesting applications.
GENTILE, MATTEO
2021/2022
Abstract
In recent years, two-dimensional (2D) materials have been widely studied for their peculiar properties which could lead to severe technological advancements. Wet-jet milling (WJM), a liquid-phase (LPE) exfoliation technique, was employed to produce graphene and 2D MoS2 flakes. In this Thesis work, I used graphene for supercapacitors (SCs) electrode slurries formulation and 2D MoS2 for proton-exchange membrane electrolyzers (PEMELs) cathode catalysts production. A H2-based thermal treatment was designed to further improve the performances of these devices, exploiting the beneficial properties given by the implementation of these materials. Supercapacitors are electrochemical energy storage devices operating at high power densities, but limited energy densities. The exploitation of graphene as electrode material has demonstrated to supply higher gravimetric capacitance (Cg), power density and rate capability to electric double layer capacitors (EDLCs). As these perks are provided by the 2D graphitic structure of graphene, the H2 thermal treatments aimed at producing a graphitization extended to the whole surface of the SCs active material. The sp2 bonds promotion and surface functionalities removal resulted in the 700 °C-treated electrodes-based EDLCs to report Cg and energy density gains of +39.4 % and +38.4 % at 1 A g-1, respectively, compared to the untreated electrodes-based EDLCs. Proton-exchange membrane electrolyzers are electrochemical energy conversion devices used for the hydrogen evolution reaction (HER). The catalytic activity reported by the Mo edge sites of 2D MoS2 could be stretched further throughout promotion of S vacancies via H2S evolution. The three-electrode cell electrochemical characterization revealed overpotential reductions by 26.7 % at -50 mA cm-2 for the 900 °C-treated 2D MoS2 catalysts compared to the untreated ones. Although laying still far (in terms of HER overpotentials) from commercially available Pt-based catalysts, the 900 °C-treated 2D MoS2-based PEMELs confirmed the reduction in cell voltage compared to the untreated 2D MoS2-based PEMELs. These results envisage open room for research on sustainable noble metals-free catalysts.File | Dimensione | Formato | |
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2022_12_GENTILE_Executive Summary.pdf
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https://hdl.handle.net/10589/197643