Combined investigation of bulk diffusion and surface exchange parameters of silver catalyst coated yttrium-doped BSCF membranes

Abstract

The combined effect of minor yttrium doping and silver catalyst deposition on the surface kinetics (k(chem)) and bulk diffusion (D(chem)) of BSCF (Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ)) perovskite membranes was explored using electrical conductivity relaxation (ECR) and validated using oxygen permeation measurements. Yttrium doping of BSCF to form Ba(0.5)Sr(0.5)Co(0.8)Fe(0.175)Y(0.025)O(3-δ) (BSCFY) improved both the surface exchange kinetics and the bulk diffusion by an average of 44% and 177% respectively, supporting improved oxygen permeation measurements. The deposition of a silver catalyst on BSCFY further improved the surface kinetics by 63-450% at intermediate operating temperatures (600-750 °C), and reduced the activation energy from 163 to 90 kJ mol(-1). Interestingly, these improvements did not translate into enhanced oxygen fluxes for the silver coated thicker 0.5 and 1 mm membranes, indicating that the oxygen ion transport was limited by bulk diffusion. However, oxygen permeation measurements on catalyst-coated 0.3 mm-thick membranes yielded improvements of 20-35% in the range 600-900 °C. The silver catalyst was beneficial in overcoming surface kinetic limitations for the thinner 0.3 mm BSCFY membranes, thus suggesting that the critical thickness of BSCFY membranes lies around ∼0.4 mm and validating the ECR measurements.

Bulk transport and oxygen surface exchange of the mixed ionic–electronic conductor Ce1−xTbxO2−δ (x = 0.1, 0.2, 0.5)

“…Commonly used techniques include isotopic exchange depth proling using, e.g., secondary ion mass spectrometry (SIMS) and electrical conductivity relaxation (ECR). [20][21][22]49 Pulse isotopic exchange (PIE) 23 and isothermal oxygen isotope equilibration 24 techniques allow working in a surface exchange-dominated regime provided that powders are employed with a particle size smaller than the so-called characteristic thickness (L c ¼ D/k).…”

Enhanced CO2 Resistance for Robust Oxygen Separation Through Tantalum‐doped Perovskite Membranes

“…For SF (Figure a), during the first 10 h period where 100 % He was used as the sweep gas, the fluxes decreased from 0.12 to 0.10 mL min −1 cm −2 , which is likely a result of the phase instability of SF. After the introduction of CO 2 for 1 h, J values were substantially reduced to 0.075 mL min −1 cm −2 ; most likely owing to the CO 2 absorption on the membrane surface . During the next 15 h period, J decreased further by 27 % (from 0.075 to 0.055 mL min −1 cm −2 ).…”

Oxygen-permeable ceramic membrane with improved mediate-temperature stability based on partially A-site doped KxSr1-xCo0.8Fe0.2O3-δ

“…Therefore, while the membrane thickness of K 0.1 Sr 0.9 Co 0.8 Fe 0.2 O 3-δ sample is decreased to 0.5 mm, it is ineffective to improve its oxygen permeation flux by further reducing the membrane thickness. The surface modification treatment with some highly active catalysts should be considered when designing practical membrane modules [38,39].…”