Reversible solid-oxide cells (rSOCs) are efficient electrochemical devices that can be utilized for the provision of energy storage services, essential to improve the flexibility and penetration of renewable sources. These feature the capability of converting electricity into chemicals via electrolysis and of delivering electric power through the electro-oxidation of fuels. rSOCs operating with CO-CO2 are of particular interest since they could foster the utilization of carbon dioxide, converting it into valuable chemicals, with the consequent reduction of atmospheric emissions. One of the most active research branches in SOCs’ field is currently focused on the study of materials for cells’ components, among which fuel electrodes play a crucial role, not only in the determination of the devices’ performance, but also of their durability. However, operation under carbonaceous feeds requires alternatives to the state-of-the-art Ni- Yttria-stabilized-zirconia (Ni-YSZ) material. In view of the better redox and coking resistance, mixed-ion-electron-conductive perovskites are promising candidates for new fuel electrode solutions. Their versatile structure also allows for a wide range of modifications, aimed at enhancing their properties. This work focuses on the investigation of the electrocatalytic properties of the SrTi0.3Fe0.7O3-d (STF), and exsolution Sr0.95(Ti0.3Fe0.63Ni0.07)O3-d (STF- Ni) perovskite-based fuel electrodes together with Ni-YSZ for reversible SOC operation under CO-CO2 and H2-H2O feed mixtures both in the short and long term. Experimental results have demonstrated better performance of the perovskite-based electrodes compared to Ni-YSZ, especially for electrolysis operation, thanks to a higher catalytic activity towards CO-CO2 and a better resistance to carbon deposition. Durability issues were however encountered during long-run polarization tests, highlighting the poor stability of the two perovskites under electrolysis operation, which induces structural modifications of the material and loss of activity. Experiments under H2-H2O evidenced the superior performance of the STF-Ni electrode with respect to both the parent STF and Ni-YSZ, thanks to the high electrochemical activity of the perovskite and the enhanced affinity to H2 provided by the Ni exsolution. The cell also resulted more stable during durability tests, opening to possible promising applications of this technology in the hydrogen sector.
Le celle reversibili a ossidi solidi (rSOC) sono dispositivi elettrochimici che potrebbero trovare utilizzo come sistemi di accumulo dell’energia, per migliorare la flessibilità e la penetrazione delle fonti rinnovabili. Sono in grado di convertire l’elettricità in specie chimiche attraverso reazioni di elettrolisi e di erogare potenza dall’elettro-ossidazione dei combustibili. Le rSOC che operano con CO-CO2 riscuotono particolare interesse poiché potrebbero favorire l’utilizzo dell’anidride carbonica, convertendola in prodotti chimici utili, con la conseguente riduzione delle emissioni in atmosfera. Uno dei rami di ricerca più attivi nel settore è attualmente rivolto allo studio dei materiali per i componenti delle celle, tra i quali gli elettrodi del combustibile ricoprono un ruolo cruciale nel determinare le prestazioni dei dispositivi e la loro durabilità. Tuttavia, alimentare le celle con combustibili a base carboniosa richiede alternative rispetto al Ni-YSZ (Ni-Zirconia-stabilizzata-con-Ittrio), l’attuale stato dell’arte. In virtù di una miglior resistenza ossidoriduttiva e al coking, oltre che alla capacità di condurre al contempo ioni ed elettroni, le perovskiti risultano candidati promettenti per lo sviluppo di nuovi tipi di elettrodi. La loro struttura versatile si presta ad una vasta gamma di modifiche, volte a potenziare le loro caratteristiche di base. Il presente lavoro mira allo studio delle proprietà elettro-catalitiche di due elettrodi per il combustibile basati su perovskiti (SrTi0.3Fe0.7O3-d (STF)) e la corrispettiva ex-soluzione (Sr0.95(Ti0.3Fe0.63Ni0.07)O3-d (STF- Ni)), assieme al Ni-YSZ, per operare reversibilmente miscele di CO-CO2 e H2-H2O nel breve e lungo termine. Sperimentalmente gli elettrodi basati su perovskiti hanno dimostrato migliori prestazioni rispetto al Ni-YSZ, specialmente in elettrolisi, grazie alla maggiore attività catalitica verso CO-CO2 e una migliore resistenza al deposito di carbonio. I test di durabilità hanno però evidenziato la scarsa stabilità delle due perovskiti in elettrolisi, a causa dei cambiamenti strutturali indotti nel materiale con la conseguente perdita di attività. Gli esperimenti in H2-H2O hanno evidenziato migliori prestazioni dell’elettrodo STF-Ni rispetto sia a STF che a Ni-YSZ, grazie all’elevata attività elettrochimica della perovskite e la migliore affinità ad H2 apportata dall’ex-soluzione di Ni. La cella è inoltre risultata più stabile durante i test di durabilità, aprendo ad una promettente applicazione di questa tecnologia nel settore dell’idrogeno.
Preparation and testing of solid oxide cells with different fuel electrode materials for reversible operation under mixtures of CO-CO2 and H2-H2O
Meneghetti, Riccardo
2022/2023
Abstract
Reversible solid-oxide cells (rSOCs) are efficient electrochemical devices that can be utilized for the provision of energy storage services, essential to improve the flexibility and penetration of renewable sources. These feature the capability of converting electricity into chemicals via electrolysis and of delivering electric power through the electro-oxidation of fuels. rSOCs operating with CO-CO2 are of particular interest since they could foster the utilization of carbon dioxide, converting it into valuable chemicals, with the consequent reduction of atmospheric emissions. One of the most active research branches in SOCs’ field is currently focused on the study of materials for cells’ components, among which fuel electrodes play a crucial role, not only in the determination of the devices’ performance, but also of their durability. However, operation under carbonaceous feeds requires alternatives to the state-of-the-art Ni- Yttria-stabilized-zirconia (Ni-YSZ) material. In view of the better redox and coking resistance, mixed-ion-electron-conductive perovskites are promising candidates for new fuel electrode solutions. Their versatile structure also allows for a wide range of modifications, aimed at enhancing their properties. This work focuses on the investigation of the electrocatalytic properties of the SrTi0.3Fe0.7O3-d (STF), and exsolution Sr0.95(Ti0.3Fe0.63Ni0.07)O3-d (STF- Ni) perovskite-based fuel electrodes together with Ni-YSZ for reversible SOC operation under CO-CO2 and H2-H2O feed mixtures both in the short and long term. Experimental results have demonstrated better performance of the perovskite-based electrodes compared to Ni-YSZ, especially for electrolysis operation, thanks to a higher catalytic activity towards CO-CO2 and a better resistance to carbon deposition. Durability issues were however encountered during long-run polarization tests, highlighting the poor stability of the two perovskites under electrolysis operation, which induces structural modifications of the material and loss of activity. Experiments under H2-H2O evidenced the superior performance of the STF-Ni electrode with respect to both the parent STF and Ni-YSZ, thanks to the high electrochemical activity of the perovskite and the enhanced affinity to H2 provided by the Ni exsolution. The cell also resulted more stable during durability tests, opening to possible promising applications of this technology in the hydrogen sector.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/209418