Functionally Graded IT-MOFC Electrolytes Based on Highly Conductive δ-Bi₂O₃–0.2 wt % B₂O₃ Composite with Molten Grain Boundaries

Abstract

Recently, the concept of an intermediate-temperature molten oxide fuel cell (IT-MOFC) has been suggested. A MOFC combines the advantages of both the MCFC (highly conductive molten electrolyte) and SOFC (air oxygen is used as an oxidant). Here, we report the performances of IT-MOFCs based on functionally graded double-layer GDC/δ-Bi 2 O 3 −0.2 wt % B 2 O 3 and YSZ/δ-Bi 2 O 3 − 0.2 wt % B 2 O 3 electrolytes in which δ-Bi 2 O 3 −0.2 wt % B 2 O 3 composite with molten grain boundaries (GBs) on the cathode side (oxidant) provides the highest oxygen ionic conductivity of 2 S cm −1 at 750 °C.The GDC or YSZ layer on the anode side (reductant) protects δ-Bi 2 O 3 −0.2 wt % B 2 O 3 from decomposing in a reducing atmosphere. The optimal thicknesses of GDC and YSZ protective layers are evaluated. By reducing the thickness of the GDC and YSZ layers to 15 and 5 μm, respectively, the power density of these IT-MOFCs can theoretically reach a value of 1 W cm −2 . This value is significantly higher than the previously reported power output for IT-MOFCs based on the matrix TeO 2 −Te 4 Bi 2 O 11 (11.5 mW cm −2 at 640 °C) and Al 2 O 3 −Na 2 W 2 O 7 (121 mW cm −2 at 750 °C) electrolytes.

Building a Green, Robust, and Efficient Bi-MOF Heterogeneous Catalyst for the Strecker Reaction of Ketones

“…Thus, bismuth compounds are usually accepted as biologically safe and nontoxic materials 1,2 and have found wide application as antibacterial and antifungal agents, 3−6 for example, bismuth sulfonates that are effective against H. pylori even when compared to commercial drugs. 7 In solid-state chemistry, bismuth compounds have been studied in important applications including high TC superconductors, 8 ferroelectric and piezoelectric materials, 9 oxide ion conductors, 10,11 catalysis, 12−16 thermoelectric materials, 17 among others. In the view of this, bismuth appears as an excellent candidate to be used in the construction of metal−organic frameworks (MOFs) because they and their derivatives are a class of emerging promising coordination materials.…”

“…pylori even when compared to commercial drugs . In solid-state chemistry, bismuth compounds have been studied in important applications including high TC superconductors, ferroelectric and piezoelectric materials, oxide ion conductors, , catalysis, − thermoelectric materials, among others. In the view of this, bismuth appears as an excellent candidate to be used in the construction of metal–organic frameworks (MOFs) because they and their derivatives are a class of emerging promising coordination materials.…”

Polymorphism and Visible-Light-Driven Photocatalysis of Doped Bi2O3:M (M = S, Se, and Re)

“…Both the oxygen-defective lattice and the polarizability of the 6s 2 lone pair of electrons of the bismuth­(III) cation in δ-Bi 2 O 3 contribute to the high oxygen ion conductivity. Therefore, the δ-phase is known as the best oxygen ion-conducting ceramic, making it suitable as a solid electrolyte − and as a gas sensing material. − Furthermore, some reports focus on the application of δ-Bi 2 O 3 as an adsorbent for water purification. − More recently, the cubic δ-modification of bismuth­(III) oxide came into focus as a semiconductor in photocatalytic processes − despite its lower efficiency compared to that of tetragonal β-Bi 2 O 3 . − In addition, δ-Bi 2 O 3 was also investigated as a vanadium-stabilized phase (δ-Bi 11 VO 19 ) , − in combination with a cocatalyst (i.e., δ-Bi 2 O 3 -Ag), and in composites such as AgX/δ-Bi 2 O 3 (X = Br, I), δ-Bi 2 O 3 /Bi 2 O 2 CO 3 , and δ-Bi 2 O 3 /Bi 2 MoO 6 . Thus, a plethora of synthetic approaches for δ-Bi 2 O 3 in the form of powders, − ,,,,− films, ,− nanosheets, and nanowires was developed.…”

“…Thus, a plethora of synthetic approaches for δ-Bi 2 O 3 in the form of powders, − ,,,,− films, ,− nanosheets, and nanowires was developed. However, stabilization of pure δ-Bi 2 O 3 at room temperature is still a challenge; therefore, the application of the metastable modification is restricted to a low number of examples. − Stabilization of δ-Bi 2 O 3 to room temperature can be achieved by doping, but it must be kept in mind that incorporation of dopants into the crystal lattice of bismuth­(III) influences the physical properties and, for example, reduces the oxygen ion conductivity by several orders of magnitude. ,− In the last decades, numerous reports have dealt with the stabilization of δ-Bi 2 O 3 using a variety of main-group elements and transition metals (B, P, Ti, , V, − Fe, Y, , Nb, , Te, Ta, Ce, − Eu, Tb, Dy, , Er, − Tm, Yb, , Lu, and Th) and double-doping (Hf/Zr, Te/V, Y/Yb, Er/Nb, Er/Gd, Ho/Gd, Ho/Dy, Dy/W, Sm/Ce, Sm/Yb, La/Mo, Pr/Mo, Dy/Tm, Gd/Lu, , Yb/Dy, , Eu, or Tb/Th…”

“…Among them, Bi 14 WO 24 is the only ternary example, for which a cubic modification was additionally reported. , In the case of compounds related to Bi 14 ReO 24.5 , the cubic δ-phase is reported for quaternary compounds with the composition Bi 12.5 Ln 1.5 ReO 24.5 (Ln = Y, , La, ,, Pr, Nd, , Sm, Eu, Gd, Dy, Ho, Er, ,, Yb, and Lu ,, ). Semi and nonmetal-stabilized δ-Bi 2 O 3 is only known for the binary systems of Bi 2 O 3 –B 2 O 3 and Bi 2 O 3 –BiPO 4 , respectively . Several compounds of the binary system Bi 2 O 3 –SO 3 such as Bi 14 O 20 (SO 4 ), Bi 8 O 11 (SO 4 ), Bi 9 O 12.5 (SO 4 ), and Bi 15 O 21.5 (SO 4 ) exhibit a fluorite -related superstructure, but corresponding cubic modifications are still unknown to date.…”