Investigations of Carbon Dioxide Electrolysis on Perovskite with Exsolved Nanoparticles in Solid Oxide Electrolysis Cell
Creators: Zhang, Bowen
Publisher: name: University of Alberta Library
Year: 2023

<p>Carbon dioxide (CO2) electrolysis, when combined with renewable energy sources, has emerged as a promising technology for reducing CO2 emissions. Integrating CO2 electrolysis into solid oxide electrolysis cell (SOEC) technology has become one of the main ways to reduce carbon emissions in the future due to its advantages of high efficiency, high selectivity, long lifespan and scalability. In recent years, significant efforts have been dedicated to developing promising electrode materials and gaining insight into the reaction mechanisms for CO2 electrolysis in SOEC, leading to the prospect of a sustainable and low-carbon future. Perovskites with exsolved nanoparticles (P-eNs) have become the most promising electrode materials, thanks to the coupling of multifunctionality of perovskite and the high activity and thermal stability of the exsolved nanoparticles. However, several challenges remain with regards to their practical applications, such as enhancing the stability performances of P-eNs and a more comprehensive understanding of CO2 electrolysis mechanisms on P-eNs based cathodes. Addressing these issues will facilitate the commercialization of CO2 electrolysis using P-eNs based materials, bringing us one step closer to a greener future.<br>
Although many efforts have been devoted to enhancing the catalytic activity of perovskite by promoting the exsolution, the remarkable degradation of P-eNs based materials, particularly at high voltages, still remains as a major challenge. In my first work, using Sr2Fe1.3Ni0.2Mo0.5O6-δ as a model example, I have demonstrated that the B-site vacancies left on the perovskite scaffold after exsolution have a great influence on the stability of P-eN-based catalysts. Through ion exchange between foreign Fe cations and bulk Ni cations in the parent perovskite, the resistance to reduction of the perovskite substrate with B-site supplement has been significantly enhanced, resulting in the improved stability performance at high voltages compared to the P-eNs without B-site supplement. Furthermore, I have put forward the degradation mechanisms based on the structural evolution of perovskite substrate to shed lights on the origin of performance deterioration of P-eNs based cathodes.<br>
In addition, the full exploitation of the heterogeneous architecture on exsolution-facilitated perovskites is still limited due to the absence of fine-regulation over the phase evolution of host perovskite during exsolution. Consequently, our current understanding on how the phase transformation of the perovskite scaffold affects the catalytic performances of P-eNs remains inadequate, leading to a lack of design guidance for exsolution-promoted P-eNs materials. In the second work, I identified a set of strategies for controlling the phase evolution of the perovskite scaffold without compromising exsolution on Sr2Fe1.2Ni0.3Mo0.5O6-δ. In particular, the trade-off between the promoted exsolution of nanoparticles and well-preserved phase structure of host perovskite has been broken by a B-site supplement strategy. Using CO2 electrolysis as an illustrative case study, we have experimentally and theoretically demonstrated that the carbon monoxide production and operating stability of P-eNs can be selectively enhanced by regulating the phase evolution of host perovskites while facilitating exsolution. My findings shed light on the significance of the phase structure of the host perovskite in catalytic reactions occurring on P-eNs. Furthermore, the effective implementation of B-site supplement strategy could potentially pave the way for ground-breaking advance in the field of catalytic chemistry.<br>
In my latest research, I have presented another novel and ingenious method involving F-doping, aimed at effectively suppressing the phase transition of Sr2Fe1.2Ni0.3Mo0.5O6-δ (SFN3M) during exsolution and enhancing the stability performances of exsolved SFN3M in CO2 electrolysis. The experimental characterizations combined with density functional theory calculations reveal that the incorporation of fluorine into SFN3M lattice is beneficial for preserving the high oxidation states of B-site cations and inhibiting the lattice oxygen loss, resulting in a robust BO6 octahedron in host perovskite. It is found that the well-preserved double perovskite structure exhibits a stronger interaction with CO2, thus enhancing the catalytic activity of F-doped exsolved SFN3M (F-SFN3M-red). Furthermore, the robust BO6 octahedron of host perovskite significantly enhances the resistance of F-SFN3M-red to decomposition under high-voltage CO2 electrolysis, leading to the significantly increased carbon monoxide productivity over a broad voltage range. These findings highlight that F doping strategy has great potential to aid the development of exsolved perovskites with high catalytic activity and stability for a wider range of electrocatalysis applications.</p>