A Promising Proton Conducting Electrolyte BaZr1-xHoxO3-δ (0.05 ≤ x ≤ 0.20) Ceramics for Intermediate Temperature Solid Oxide Fuel Cells

Abstract

In this study, the Ho-substituted BaZrO 3 electrolyte ceramics (BaZr 1-x Ho x o 3-δ , 0.05 ≤ x ≤ 0.20) were synthesized through a low-cost flash pyrolysis process followed by conventional sintering. The effects of Ho-substitution in BaZrO 3 studied in terms of the structural phase relationship, microstructure and electrical conductivity to substantiate augmented total electrical conductivity for intermediate temperature solid oxide fuel cells (IT-SOFCs). The Rietveld refined X-ray diffraction (XRD) patterns revealed that pure phase with Pm m 3 space group symmetry of cubic crystal system as originated in all samples sintered at 1600 °C for 8 h. The Raman spectroscopic investigations also approved that Ho incorporation in BaZro 3 ceramics. Field Emission Scanning Microscopic (FESEM) study informed a mixture of fine and coarse grains in the fracture surface of Ho-substituted BaZrO 3 sintered samples. The relative density and average grain size of samples were observed to decrease as per the addition of Hosubstitution in BaZro 3 ceramics. The electrical conductivity study was accomplished by Electrical Impedance Spectroscopy (EIS) under 3% humidified O 2 atmosphere from 300 to 800 °C. Furthermore, the total electrical conductivity of BaZr 0.8 Ho 0.2 o 3-δ ceramic was found to be 5.8 × 10 −3 S-cm −1 at 600 °C under 3% humidified atmosphere, which may be a promising electrolyte for IT-SOFCs. Recently, the proton conductive oxide ceramics have fascinated worldwide attention due to widespread applications in intermediate temperature solid oxide fuel cells (IT-SOFCs), hydrogen separation and electrolysis of steam, etc. In this context, the rare-earth cerates and zirconates with the perovskite-type A(II)B(IV)O 3 crystallographic structure are the two foremost families of proton-conducting oxides for electrochemical applications 1-4. Generally, in these categories of oxide materials, oxygen vacancies are increased by replacement of tetravalent cation B(IV) by trivalent cation M(III) as given in the Eq. (1) using Kröger-Vink notation.

Mn Additive Improves Zr Grain Boundary Diffusion for Sintering of a Y-Doped BaZrO3 Proton Conductor

“…12,13 However, the introduction of Y 3+ (r = 0.90 Å for 6-fold coordination) as a dopant reduces the tolerance factor down to 0.987 at 20% Y-doped BZO, leading to local distortions that can impede proton transport. 17 The sintering additives studied in the literature, with an ionic radius larger than Zr 4+ (r VI = 0.72 Å), such as Zn 2+ (r VI = 0.74 Å), Cu 2+ (r VI = 0.73 Å), Ho 3+ (r VI = 0.90 Å), or Ce 4+ (r VI = 0.87 Å), 22,44,45 are likely to have a detrimental impact on proton conductivity by reducing the tolerance factor even further. In contrast, the proposition of the smaller Mn 3+ ion (r VI = 0.64 Å), confirmed through our prior study, 25 has the potential to restore the BZY tolerance factor toward unity (Figure 1b).…”

Electron Density Distribution using Maximum Entropy Method and Conductivity Studies of Highly Dense BaZr0.85Ho0.10Y0.025Nd0.025O3-δ Electrolyte Ceramic for Intermediate Temperature Solid Oxide Fuel Cells

“…Furthermore, our research group previously investigated Ho-doped BaZrO3 system and found 91.1% relative density for BaZr0.8Ho0.2O3-δ sintered at 1600 ℃ for 8 h with 1.11×10 -3 S-cm -1 total conductivity at 650 ℃ in 3% humidified atmosphere [25]. Similarly, Saini et al reported 99.1% relative density for spark plasma sintered BaZr0.8Ho0.2O3-δ with 9.64×10 -2 S-cm -1 total conductivity at 700 ℃ in 3% humidified atmosphere [26].…”

Self-assembly of water-filled molecular saddles to generate diverse morphologies and high proton conductivity

“…6 Designing efficient SSPC materials is crucial for advancing clean and renewable energy technologies and overcoming certain challenges related to conventional proton-conducting systems. 7,8 The current SSPC materials based on metalorganic frameworks (MOFs), [9][10][11][12] carbon-organic frameworks (COFs), [13][14][15][16] polymer electrolytes, [17][18][19] perovskite oxide, [20][21][22][23][24] etc. offer limited solution processability and the use of metal ions can lead to adverse environmental consequences and loss of activity upon leaching of metal ions.…”