Design principle and assessing the correlations in Sb-doped Ba0.5Sr0.5FeO3–δ perovskite oxide for enhanced oxygen reduction catalytic performance

Tailoring the d-band electronic structure of deficient LaMn0.3Co0.7O3-δ perovskite nanofibers for boosting oxygen electrocatalysis in Zn-Air batteries

The development and design of efficient bifunctional electrocatalysts towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are crucial for rechargeable Zinc-air batteries (ZABs). Optimizing the d-band structure of active metal center in perovskite oxides is an effective method to enhance ORR/OER activity by accelerating the rate-determining step. Herein, we report a deficient method to optimize the d-band structure of Co ions in LaMn0.3Co0.7O3-δ (LMCO-2) perovskite nanofibers, which regulates the mutual effect between B-site Co ions and reactive oxygen intermediates. It is proved by experiment and theoretical calculation that the d-band center (Md) of transition metal ions in LMCO-2 is moved up and the electron filling number of eg orbital in B site is 1.01, thus leading to the reduction of Gibbs free energy required for ORR rate-determining step (OH*→H2O*) to 0.22 eV and promoting reaction proceeds. In this manner, LMCO-2 showed good bifunctional oxygen electrocatalytic activity, with a half-wave potential of 0.71 V vs. RHE. Furthermore, the high specific capacity of 811.54 mAh g-1 and power density of 326.56 mW cm-2 were obtained by using LMCO-2 as the cathode catalyst for ZABs. This study proved the feasibility of d-band structure regulation to enhance the electrocatalytic activity of perovskite oxides.

Improved Ionic Transport Using a Novel Semiconductor Co0.6Mn0.4Fe0.4Al1.6O4 and Its Heterostructure with Zinc Oxide for Electrolyte Membrane in LT-CFCs

Improving the ionic conductivity and slow oxygen reduction electro-catalytic activity of reactions occurring at low operating temperature would do wonders for the widespread use of low-operating temperature ceramic fuel cells (LT-CFCs; 450-550 °C). In this work, we present a novel semiconductor heterostructure composite made of a spinel-like structure of Co_0.6Mn_0.4Fe_0.4Al_1.6O₄ (CMFA) and ZnO, which functions as an effective electrolyte membrane for solid oxide fuel cells. For enhanced fuel cell performance at sub-optimal temperatures, the CMFA-ZnO heterostructure composite was developed. We have shown that a button-sized SOFC fueled by H₂ and ambient air can provide 835 mW/cm² of power and 2216 mA/cm² of current at 550 °C, possibly functioning down to 450 °C. In addition, the oxygen vacancy formation energy and activation energy of the CMFA-ZnO heterostructure composite is lower than those of the individual CMFA and ZnO, facilitating ion transit. The improved ionic conduction of the CMFA-ZnO heterostructure composite was investigated using several transmission and spectroscopic measures, including X-ray diffraction, photoelectron, and UV-visible spectroscopy, and density functional theory (DFT) calculations. These findings suggest that the heterostructure approach is practical for LT-SOFCs.

High-performing and stable semiconductor yttrium-doped gadolinium electrolyte for low-temperature solid oxide fuel cells

High-performing electrolytes at low operating temperatures have become an inevitable trend in the development of low-temperature solid oxide fuel cells (LT-SOFCs). Such electrolytes have drawn significant attention due to their appeal for high performance. Herein, we propose a new material by doping Y³⁺ into Gd₂O₃ for LT-SOFC electrolyte use. The prepared material was characterized in terms of crystal structure, surface, and interface properties, followed by its application in LT-SOFCs. YDG delivered promising SOFC performance with a power density of 1046 mW cm^-2 at 550 °C along with high ionic conductivity of 0.19 S cm^-1. Moreover, impedance spectra revealed that YDG exhibited the least ohmic resistance of 0.06-0.09 Ω cm² at 550-460 °C. Furthermore, stable operation for 60 h demonstrated the chemical stability of the material in reduced temperature environments. Density function theory was also applied to analyze the electronic band structure and density of states of the synthesized sample. Our findings thus certify that YDG as a high-performing electrolyte at low operating temperatures.

Oxygen Vacancy and Valence Band Structure of Ba0.5Sr0.5Fe1-xCuxO3-δ (x = 0-0.15) with Enhanced ORR Activity for IT-SOFCs

The oxygen reduction reaction (ORR) activity of a Cu-doped Ba_0.5Sr_0.5FeO_3-δ (Ba_0.5Sr_0.5Fe_1-xCu_xO_3-δ, BSFCux, x = 0, 0.05, 0.10, 0.15) perovskite cathode was investigated in terms of oxygen vacancy formation and valence band structure. The BSFCux (x = 0, 0.05, 0.10, 0.15) crystallized in a cubic perovskite structure (Pm3¯m). By thermogravimetric analysis and surface chemical analysis, it was confirmed that the concentration of oxygen vacancies in the lattice increased with Cu doping. The average oxidation state of B-site ions decreased from 3.583 (x = 0) to 3.210 (x = 0.15), and the valence band maximum shifted from -0.133 eV (x = 0) to -0.222 eV (x = 0.15). The electrical conductivity of BSFCux increased with temperature because of the thermally activated small polaron hopping mechanism showing a maximum value of 64.12 S cm^-1 (x = 0.15) at 500 °C. The ASR value as an indicator of ORR activity decreased by 72.6% from 0.135 Ω cm² (x = 0) to 0.037 Ω cm² (x = 0.15) at 700 °C. The Cu doping increased oxygen vacancy concentration and electron concentration in the valence band to promote electron exchange with adsorbed oxygen, thereby improving ORR activity.

Modulating the Energy Band Structure of the Mg-Doped Sr0.5Pr0.5Fe0.2Mg0.2Ti0.6O3-δ Electrolyte with Boosted Ionic Conductivity and Electrochemical Performance for Solid Oxide Fuel Cells

Achieving fast ionic conductivity in the electrolyte at low operating temperatures while maintaining the stable and high electrochemical performance of solid oxide fuel cells (SOFCs) is challenging. Herein, we propose a new type of electrolyte based on perovskite Sr_0.5Pr_0.5Fe_0.4Ti_0.6O_3-δ for low-temperature SOFCs. The ionic conducting behavior of the electrolyte is modulated using Mg doping, and three different Sr_0.5Pr_0.5Fe_0.4-xMg_xTi_0.6O_3-δ (x = 0, 0.1, and 0.2) samples are prepared. The synthesized Sr_0.5Pr_0.5Fe_0.2Mg_0.2Ti_0.6O_3-δ (SPFMg_0.2T) proved to be an optimal electrolyte material, exhibiting a high ionic conductivity of 0.133 S cm^-1 along with an attractive fuel cell performance of 0.83 W cm^-2 at 520 °C. We proved that a proper amount of Mg doping (20%) contributes to the creation of an adequate number of oxygen vacancies, which facilitates the fast transport of the oxide ions. Considering its rapid oxide ion transport, the prepared SPFMg_0.2T presented heterostructure characteristics in the form of an insulating core and superionic conduction via surface layers. In addition, the effect of Mg doping is intensively investigated to tune the band structure for the transport of charged species. Meanwhile, the concept of energy band alignment is employed to interpret the working principle of the proposed electrolyte. Moreover, the density functional theory is utilized to determine the perovskite structures of SrTiO_3-δ and Sr_0.5Pr_0.5Fe_0.4-xMg_xTi_0.6O_3-δ (x = 0, 0.1, and 0.2) and their electronic states. Further, the SPFMg_0.2T with 20% Mg doping exhibited low dissociation energy, which ensures the fast and high ionic conduction in the electrolyte. Inclusively, Sr_0.5Pr_0.5Fe_0.4Ti_0.6O_3-δ is a promising electrolyte for SOFCs, and its performance can be efficiently boosted via Mg doping to modulate the energy band structure.

Nickel-iron nanoparticles encapsulated in carbon nanotubes prepared from waste plastics for low-temperature solid oxide fuel cells

Low-temperature solid oxide fuel cells (LT-SOFCs) are a promising next-generation fuel cell due to their low cost and rapid start-up, posing a significant challenge to electrode materials with high electrocatalytic activity. Herein, we reported the bimetallic nanoparticles encapsulated in carbon nanotubes (NiFe@CNTs) prepared by carefully controlling catalytic pyrolysis of waste plastics. Results showed that plenty of multi-walled CNTs with outer diameters (14.38 ± 3.84 nm) were observed due to the smallest crystalline size of Ni-Fe alloy nanoparticles. SOFCs with such NiFe@CNTs blended in anode exhibited remarkable performances, reaching a maximum power density of 885 mW cm⁻² at 500°C. This could be attributed to the well-dispersed alloy nanoparticles and high graphitization degree of NiFe@CNTs to improve HOR activity. Our strategy could upcycle waste plastics to produce nanocomposites and demonstrate a high-performance LT-SOFCs system, addressing the challenges of sustainable waste management and guaranteeing global energy safety simultaneously.

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The M@CNTs from the waste plastics were utilized as anode additive of LT-SOFCs

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The effects of active metal species on the quality of nanocomposite were studied

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Maximum power density of 885 mW cm⁻² at 500°C was obtained with NiFe@CNTs

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The excellent performances of SOFCs could be attributed to the improved HOR activity