Quantifying Electrochemical Driving Force for Exsolution in Perovskite Oxides by Designing Graded Oxygen Chemical Potential

A-site-deficiency range identified for in situ exsolution from (La0.4Sr0.6)1-αTi0.95Ni0.05O3±δ electrodes for SOFC and SOEC

Modulating the A-site deficiency is a useful method to achieve the exsolution of nanoparticles on the surface of perovskite, improving the catalytic activity. However, rules for designing the deficiency value and its roles on the structure and performance remain unclear. In this study, a wide range of A-site deficiencies of (La0.4Sr0.6)1-αTi0.95Ni0.05O3±δ (LSTN, α = 0.00, 0.13, 0.15, and 0.18) titanate perovskite materials was designed to systematically investigate their crystal structure, binding energy, oxygen vacancy concentration, exsolution process, and electrochemical performance. An extremely high conductivity (e.g., 331.75 S cm-1@800 °C, 5% H2/Ar) was obtained in parallel with enhanced catalytical activity in SOFC and SOEC modes. The A-site-deficient samples displayed a higher conductivity, oxygen vacancy concentration, and power output than the stoichiometric samples (α = 0.00). The best maximum power density of 78.74 mW cm-2 and the highest population density of 25 particles per μm2 were obtained on the deficient LSTN with α = 0.13. These findings suggest that LSTN is an exceptionally promising material for solid oxide cell (SOC) electrodes.

New trends in nanoparticle exsolution

Many relevant high-temperature chemical processes require the use of oxide-supported metallic nanocatalysts. The harsh conditions under which these processes operate can trigger catalyst degradation via nanoparticle sintering, carbon depositions or poisoning, among others. This primarily affects metallic nanoparticles created via deposition methods with low metal-support interaction. In this respect, nanoparticle exsolution has emerged as a promising method for fabricating oxide-supported nanocatalysts with high interaction between the metal and the oxide support. This is due to the mechanism involved in nanoparticle exsolution, which is based on the migration of metal cations in the oxide support to its surface, where they nucleate and grow as metallic nanoparticles partially embedded in the oxide. This anchorage confers high robustness against sintering or coking-related problems. For these reasons, exsolution has attracted great interest in the last few years. Multiple works have been devoted to proving the high catalytic stability of exsolved metallic nanoparticles in several applications for high-temperature energy storage and conversion. Additionally, considerable attention has been directed towards understanding the underlying mechanism of metallic nanoparticle exsolution. However, this growing field has not been limited to these types of studies and recent discoveries at the forefront of materials design have opened new research avenues. In this work, we define six new trends in nanoparticle exsolution, taking a tour through the most important advances that have been recently reported.

In Situ Self-Assembled Active and Stable Ir@MnOx/La0.7Sr0.3Cr0.9Ir0.1O3-δ Interfaces for CO2 Electrolysis

Solid oxide electrolysis cells are prospective approaches for CO2 utilization but face significant challenges due to the sluggish reaction kinetics and poor stability of the fuel electrodes. Herein, we strategically addressed the long-standing trade-off phenomenon between enhanced exsolution and improved structural stability via topotactic ion exchange. The surface dynamic reconstruction of the MnOx/La0.7Sr0.3Cr0.9Ir0.1O3-δ (LSCIr) catalyst was visualized at the atomic scale. Compared with the Ir@LSCIr interface, the in situ self-assembled Ir@MnOx/LSCIr interface exhibited greater CO2 activation and easily removable carbonate intermediates, thus reached a 42 % improvement in CO2 electrolysis performance at 1.6 V. Furthermore, an improved CO2 electrolysis stability was achieved due to the uniformly wrapped MnOx shell of the Ir@MnOx/LSCIr cathode. Our approach enables a detailed understanding of the dynamic microstructure evolution at active interfaces and provides a roadmap for the rational design and evaluation of efficient metal/oxide catalysts for CO2 electrolysis.

External Voltage-Induced Restructuring of the Solid-State Electrode/Electrolyte Interface Revealed by X-ray Photoelectron Spectroscopy Depth Profiling Analysis

Solid/solid interfaces between electrodes and electrolytes play an important role in all-solid-state energy devices, while microscopic investigations of the buried interfaces remain challenging. Here, we construct metal|yttria-stabilized zirconia (YSZ)|Au model cells consisting of a metal film cathode (metal (M) = Au, Ni, and Ag), a single crystalline YSZ electrolyte, and a Au film anode, and use quasi in situ X-ray photoelectron spectroscopy depth profiling analysis to investigate the restructuring of buried interfaces between metal cathodes and YSZ. After applying 2.9 V at 500 °C, interfacial Zr4+ ions in the electrolyte are reduced and then interdiffuse with metal cathode overlayers, forming a miscible ZrM alloy interlayer. The interface restructuring degree follows the sequence of Au|YSZ|Au > Ni|YSZ|Au > Ag|YSZ|Au. Meanwhile, surface segregation of Zr on the cathode surface is also observed, whose degree follows the sequence of Ag|YSZ|Au > Ni|YSZ|Au > Au|YSZ|Au. Notably, the strong ZrM alloy formation enhances the interface restructuring but suppresses the Zr surface segregation. This work provides a fundamental understanding of the interfacial reaction at the buried electrode/electrolyte interface.

Metal exsolution from perovskite-based anodes in solid oxide fuel cells

Solid oxide fuel cells (SOFCs) are highly efficient and environmentally friendly devices for converting fuel into electrical energy. In this regard, metal nanoparticles (NPs) loaded onto the anode oxide play a crucial role due to their exceptional catalytic activity. NPs synthesized through exsolution exhibit excellent dispersion and stability, garnering significant attention for comprehending the exsolution process mechanism and consequently improving synthesis effectiveness. This review presents recent advancements in the exsolution process, focusing on the influence of oxygen vacancies, A-site defects, lattice strain, and phase transformation on the variation of the octahedral crystal field in perovskites. Moreover, we offer insights into future research directions to further enhance our understanding of the mechanism and achieve significant exsolution of NPs on perovskites.