Tuning Ternary Alloyed Nanoparticle Composition and Morphology by Exsolution in Double Perovskite Electrodes for CO₂ Electrolysis

Abstract

The intermittent nature of renewable energy resources makes imperative the development of efficient energy storage technologies. Solid oxide electrolysis cells (SOECs) are a promising alternative to energy conversion devices. SOECs can play an important role in the control of greenhouse gases by improving processes such as CO2 electrolysis. In order to enhance SOEC performance, exsolution of metal nanoparticles is emerging for the catalytic surface functionalization of electrodes, preventing sintering issues related to classical impregnation methods and enabling tailoring specific catalytic functions. In this work, a medium-entropy, double perovskite system Sr x FeCo0.2Ni0.2Mn0.1Mo0.5O6−δ (x = 2.0, 1.9, and 1.8) was studied. We provide evidence of Fe–Co–Ni ternary alloyed exsolved nanoparticles, revealing that the alloy composition can be tuned by adjusting the reducing conditions. Exsolution temperature is critical for Fe content in nanoparticles, increasing as temperature increases, but Ni and Co are not significantly affected. Temperature adjustments allowed control over nanoparticle size and population, shrinking and growing, respectively, as temperature decreases. In contrast to what is usually described, A-site deficiency resulted in a decrease in nanoparticle exsolution because of NiO phase formation in x = 1.9 and 1.8, so that the x = 2.0 compound outperformed both non-stoichiometric materials, showing significantly larger populations. The three compounds exhibit important conductivity under both oxidizing and reducing atmospheres, which makes them promising electrodes. The Sr2FeCo0.2Ni0.2Mn0.1Mo0.5O6−δ material was integrated as a cathode in an asymmetrical electrolyte-supported cell, and its electrochemical performance under CO2 electrolysis conditions was studied. Our results showed a boost in electrocatalytic activity upon exsolution at 600 °C when compared to the fuel electrode without exsolved nanoparticles or exsolved at 800 °C, where the appearance of the secondary Ruddlesden-Popper phase was observed. Overall, here, we proved the possibility of obtaining ternary alloy exsolved nanoparticles and tuning their composition to enhance the performance of SOEC devices, paving the path for optimized metal-alloyed exsolved nanoparticle design, which might extend its applicability to other electrocatalytic processes in energy conversion and storage.

Phase Transition Engineering of Host Perovskite toward Optimal Exsolution‐facilitated Catalysts for Carbon Dioxide Electrolysis

“…Filed emission‐scanning electron microscopy (FE‐SEM) and STEM‐EDS results substantiate that the Fe−Ni alloy nanoparticles, characterized by a larger size and increased population, have been evenly anchored on the surface of SFN 3 M+1.2Fe‐red‐2h via a thermodynamically favorable ion‐swapping process (Figures 1c(i, ii) and S5) [12, 26] . However, as a result of the extended exsolution and Ostwald ripening, the exsolved Fe−Ni nanoparticles exhibit the larger size and less population on the surface of SFN 3 M‐red‐10h (Figures 1c(i, iii) and S5) [5, 27, 28] . Furthermore, Fe/Ni ratios of exsolved nanoparticles on SFN 3 M+1.2Fe‐red‐2h and SFN 3 M‐red‐10h are 2.72 and 1.29, respectively, higher than 0.67 on DLP‐NPs (Figures S2, S6 and Table S1).…”

“…[12,26] However, as a result of the extended exsolution and Ostwald ripening, the exsolved FeÀ Ni nanoparticles exhibit the larger size and less population on the surface of SFN 3 M-red-10h (Figures 1c(i, iii) and S5). [5,27,28] Furthermore, Fe/Ni ratios of exsolved nanoparticles on SFN 3 M + 1.2Fe-red-2h and SFN 3 M-red-10h are 2.72 and 1.29, respectively, higher than 0.67 on DLP-NPs (Figures S2, S6 and Table S1). Based on the characterization presented thus far, we can draw the conclusion that DP-NPs (simplified from SFN 3 M + 1.2Fered-2h) and LP-NPs (simplified from SFN 3 M-red-10h) have been successfully constructed.…”

“…Figure S1 shows that the crystalline structure of SFN 3 M presents a pattern corresponding to DP‐typed Sr 2 FeMoO 6 (PDF#00‐060‐0459), while the LP‐typed Sr 3 FeMoO 6.5 (PDF#00‐052‐1715) as an emerging phase can be probed after reduction at 850 °C for 2 h (SFN 3 M‐red‐2h) [5, 24] . Secondary electron‐scanning transmission electron microscopy (SE‐STEM) and STEM with energy‐dispersive X‐ray spectroscopy (STEM‐EDS) results confirm the formation of Fe−Ni alloy on the surface of SFN 3 M‐red‐2h (Figure S2), demonstrating that a composite substrate composed of DP and LP with the exsolved Fe−Ni alloy nanoparticles (DLP‐NPs) has been well‐constructed (Figure 1a(i)).…”

“…Perovskites with exsolved nanoparticles (P-eNs) have been extensively used as the electrocatalysts in solid oxide cells for energy conversion and storage. [1][2][3][4] In recent years, significant efforts have been made to modify the size, density and composition of exsolved nanoparticles, [5][6][7][8][9][10] thereby improving the catalytic activity of P-eNs. [11] However, the perovskite scaffold, which plays a crucial role in extending the surface triple phase boundary and preserving the highly active sites, has received relatively little attention.…”

Co-Exsolution of Ni-Based Alloy Catalysts for the Valorization of Carbon Dioxide and Methane

“…The exsolution process can also be used to form higher-order alloy nanoparticles with three or more metals. , We studied the influence of the partial substitution of Fe with Ni and Co, which alters the kinetics of exsolution, nanoparticle growth dynamics, and catalyst nanoparticle composition. The exsolution of NiFeCo nanoparticles from the La­(Fe, Ni, Co)­O 3 perovskite oxide precursor was explored to improve the oxophilicity and thermal stability of the NiFe nanoparticles for the DRM reaction.…”