Silver-Modified Ba_1–xCo_0.7Fe_0.2Nb_0.1O_3−δ Perovskite Performing as a Cathodic Catalyst of Intermediate-Temperature Solid Oxide Fuel Cells

Abstract

A series of silver (Ag)-modified barium cobalt ferrous niobate (Ba1–x Co0.7Fe0.2Nb0.1O3‑δ, BCFN) materials were fabricated using a solid-state method by doping silver cations into the A-site of this perovskite matrix (Ag-BCFN). The electrochemical analyses indicated that the Ag-BCFN cathodic catalysts performed superior to the nonmodified catalysts when applied in intermediate-temperature solid oxide fuel cells (IT-SOFCs). These Ag-BCFN cathodic catalysts displayed a cubic perovskite structure (PDF 75-0227, Pm3̅m, α = 90°) with a high degree of crystallinity, as demonstrated by X-ray powder diffraction analyses. It was also found that the in situ exsolution of the silver ion (Ag+) occurred, where 57.9% of doped Ag+ was reduced into metallic Ag particles with size ranging from 5 to 10 nm, as shown by electron microscopic analyses. The cerium gadolinium oxide (Ce0.9Gd0.1O2−δ) electrolyte-supported symmetrical half cell using different Ag-BCFN formulations of Ba1–x Ag x Co0.7Fe0.2Nb0.1O3‑δ as electrodes showed a polarization resistance as low as 0.233 Ω·cm2 and an exchange current density of 85.336 mA·cm–2 at 650 °C under ambient pressure. The improved electrochemical kinetics is anticipated to be attributed to two reasons: doping of ions (Ag+) in the A-site of perovskite and in situ exsolved silver nanoparticles (Ag NPs) along the edge and on the surface of BCFNs improving the mobile charge and electrical properties of the material. The remaining Ag+ in the A-site induced the electron redistribution, whereas the Ag NPs were found to increase the electrochemically active sites and enable the formation of a triple-phase boundary. These explanations were confirmed by the density functional theory study, indicating that Ag-doping processes lead to a decrease in the formation energy of oxygen vacancies from 1.72 to 1.42 eV upon the partial substitution of Ba2+ by Ag+ cations.

Promotion of A-Site Ag-Doped Perovskites for the Catalytic Oxidation of Soot: Synergistic Catalytic Effect of Dual Active Sites

“…Under such conditions, not all silver was doped into the perovskite lattice and the in situ exsolution of Ag occurred. 41 No XRD peaks related to Ag 2 O and AgO were observed in all diffraction patterns. This is possible because the particles were highly dispersed on the surface of the catalyst, making it difficult to be detected by XRD.…”

“…Figure displays the XPS analysis of the La (1– x ) Ag x CoO 3 samples. Typically, the 3d 5/2 binding energies of Ag 0 and Ag + are at 368.3 and 367.3 eV, respectively. , For LA 2.5 C, the Ag 3d 5/2 binding energy is at 367.3 eV, shown in Figure A, suggesting the Ag + substitution in LC. With the further increase of Ag content in LC, a new Ag 3d 5/2 peak appeared at 368.3 eV, indicating the presence of Ag 0 .…”

“…With the increase of Ag content, the intensity of the Ag diffraction peaks was further increased. Under such conditions, not all silver was doped into the perovskite lattice and the in situ exsolution of Ag occurred …”

“…However, with the increase of Ag, the intensity of the α peak was reduced, while the intensity of the β peak was increased significantly and moved to a lower temperature as well. Combined with the catalytic activity data in Figure A,B, LA 5.0 C with the highest β peak, the catalytic oxidation activity did not improve further, which shows that the β peak did not play a decisive role in the oxidation. , …”

“…Combined with the catalytic activity data in Figure 1A,B, LA 5.0 C with the highest β peak, the catalytic oxidation activity did not improve further, which shows that the β peak did not play a decisive role in the oxidation. 39,41 The consumption of H 2 , O 2 , and NO in the test temperature range is summarized in Table S2. With the peak areas normalized by the catalyst weight.…”