Novel bifunctional tantalum and bismuth co-doped perovskite BaBi0.05Co0.8Ta0.15O3−δ with high oxygen permeation

Research on the Influence of Core Sensing Components on the Performance of Galvanic Dissolved Oxygen Sensors

The galvanic dissolved oxygen sensor finds widespread applications in multiple critical fields due to its high precision and excellent stability. As its core sensing components, the oxygen-permeable membrane, electrode, and electrolyte significantly impact the sensor's performance. To systematically investigate the comprehensive effects of these core sensing components on the performance of galvanic dissolved oxygen sensors, this study selected six types of oxygen-permeable membranes made from two materials (Perfluoroalkoxy Polymer (PFA) and Fluorinated Ethylene Propylene Copolymer (FEP)) with three thicknesses (0.015 mm, 0.03 mm, and 0.05 mm). Additionally, five concentrations of KCl electrolyte were configured, and four different proportions of lead-tin alloy electrodes were chosen. Single-factor and crossover experiments were conducted using the OxyGuard dissolved oxygen sensor as the experimental platform. The experimental results indicate that under the same membrane thickness conditions, PFA membranes provide a higher output voltage compared to FEP membranes. Moreover, the oxygen permeability of FEP membranes is more significantly affected by temperature. Furthermore, the oxygen permeability of the membrane is inversely proportional to its thickness; the thinner the membrane, the better the oxygen permeability, resulting in a corresponding increase in sensor output voltage. When the membrane thickness is reduced from 0.05 mm to 0.015 mm, the sensor output voltage for PFA and FEP membranes increases by 86% and 74.91%, respectively. However, this study also observed that excessively thin membranes might compromise measurement accuracy. In a saturated, dissolved oxygen environment, the sensor output voltage corresponding to the six oxygen-permeable membranes used in the experiment exhibits a highly linear inverse relationship with temperature (correlation coefficient ≥ 98%). Meanwhile, the lead-tin ratio of the electrode and electrolyte concentration have a relatively minor impact on the sensor output voltage, demonstrating good stability at different temperatures (coefficient of variation ≤ 0.78%). In terms of response time, it is directly proportional to the thickness of the oxygen-permeable membrane, especially for PFA membranes. When the thickness increases from 0.015 mm to 0.05 mm, the response time extends by up to 2033.33%. In contrast, the electrode material and electrolyte concentration have a less significant effect on response time. To further validate the practical value of the experimental results, the best-performing combination of core sensing components from the experiments was selected to construct a new dissolved oxygen sensor. A performance comparison test was conducted between this new sensor and the OxyGuard dissolved oxygen sensor. The results showed that both sensors had the same response time (49 s). However, in an anaerobic environment, the OxyGuard sensor demonstrated slightly higher accuracy by 2.44%. This study not only provides a deep analysis of the combined effects of oxygen-permeable membranes, electrodes, and electrolytes on the performance of galvanic dissolved oxygen sensors but also offers scientific evidence and practical guidance for optimizing sensor design.

Zirconium and Yttrium Co-Doped BaCo0.8Zr0.1Y0.1O3-δ: A New Mixed-Conducting Perovskite Oxide-Based Membrane for Efficient and Stable Oxygen Permeation

Oxygen permeation membranes (OPMs) are regarded as promising technology for pure oxygen production. Among various materials for OPMs, perovskite oxides with mixed electron and oxygen-ion (e^-/O^2-) conducting capability have attracted particular interest because of the high O^2- conductivity and structural/compositional flexibility. However, BaCoO_3-δ-based perovskites as one of the most investigated OPMs suffer from low oxygen permeation rate and inferior structural stability in CO₂-containing atmospheres. Herein, zirconium and yttrium co-doped BaCoO_3-δ (BaCo_1-2xZr_xY_xO_3-δ, x = 0, 0.05, 0.1 and 0.15) are designed and developed for efficient and stable OPMs by stabilizing the crystal structure of BaCoO_3-δ. With the increased Zr/Y co-doping content, the crystal structural stability of doped BaCoO_3-δ is much improved although the oxygen permeation flux is slightly reduced. After optimizing the co-doping amount, BaCo_0.8Zr_0.1Y_0.1O_3-δ displays both a high rate and superior durability for oxygen permeation due to the well-balanced grain size, oxygen-ion mobility, crystal structural stability, oxygen vacancy concentration and surface exchange/bulk diffusion capability. Consequently, the BaCo_0.8Zr_0.1Y_0.1O_3-δ membrane delivers a high oxygen permeation rate of 1.3 mL min^-1 cm^-2 and relatively stable operation at 800 ∘C for 100 h. This work presents a promising co-doping strategy to boost the performance of perovskite-based OPMs, which can promote the industrial application of OPM technology.

A CO2 -Tolerant Perovskite Oxide with High Oxide Ion and Electronic Conductivity

Mixed ionic-electronic conductors (MIECs) that display high oxide ion conductivity (σ_o ) and electronic conductivity (σ_e ) constitute an important family of electrocatalysts for a variety of applications including fuel cells and oxygen separation membranes. Often MIECs exhibit sufficient σ_e but inadequate σ_o . It has been a long-standing challenge to develop MIECs with both high σ_o and stability under device operation conditions. For example, the well-known perovskite oxide Ba_0.5 Sr_0.5 Co_0.8 Fe_0.2 O_{3- δ} (BSCF) exhibits exceptional σ_o and electrocatalytic activity. The reactivity of BSCF with CO₂ , however, limits its use in practical applications. Here, the perovskite oxide Bi_0.15 Sr_0.85 Co_0.8 Fe_0.2 O_{3- δ} (BiSCF) is shown to exhibit not only exceptional bulk transport properties, with a σ_o among the highest for known MIECs, but also high CO₂ tolerance. When used as an oxygen separation membrane, BiSCF displays high oxygen permeability comparable to that of BSCF and much higher stability under CO₂ . The combination of high oxide transport properties and CO₂ tolerance in a single-phase MIEC gives BiSCF a significant advantage over existing MIECs for practical applications.

Designing CO2-resistant oxygen-selective mixed ionic-electronic conducting membranes: guidelines, recent advances, and forward directions

CO₂ resistance is an enabling property for the wide-scale implementation of oxygen-selective mixed ionic-electronic conducting (MIEC) membranes in clean energy technologies, i.e., oxyfuel combustion, clean coal energy delivery, and catalytic membrane reactors for greener chemical synthesis. The significant rise in the number of studies over the past decade and the major progress in CO₂-resistant MIEC materials warrant systematic guidelines on this topic. To this end, this review features the pertaining aspects in addition to the recent status and advances of the two most promising membrane materials, perovskite and fluorite-based dual-phase materials. We explain how to quantify and design CO₂ resistant membranes using the Lewis acid-base reaction concept and thermodynamics perspective and highlight the relevant characterization techniques. For perovskite materials, a trade-off generally exists between CO₂ resistance and O₂ permeability. Fluorite materials, despite their inherent CO₂ resistance, typically have low O₂ permeability but this can be improved via different approaches including thin film technology and the recently developed minimum internal electronic short-circuit second phase and external electronic short-circuit decoration. We then elaborate the two main future directions that are centralized around the development of new oxide compositions capable of featuring simultaneously high CO₂ resistance and O₂ permeability and the exploitation of phase reactions to create a new conductive phase along the grain boundaries of dual-phase materials. The final part of the review discusses various complimentary characterization techniques and the relevant studies that can provide insights into the degradation mechanism of oxide-based materials upon exposure to CO₂.

Filter paper derived cross-linked interconnected BaBi0.2Co0.35Fe0.45O3−δ morphology with an enhanced oxygen permeation property

Membrane synthesized by filter paper templating method shows higher oxygen permeation flux than similar type membranes developed by conventional methodologies.

Hierarchical Mesoporous/Macroporous Perovskite La0.5Sr0.5CoO3-x Nanotubes: A Bifunctional Catalyst with Enhanced Activity and Cycle Stability for Rechargeable Lithium Oxygen Batteries

Perovskites show excellent specific catalytic activity toward both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline solutions; however, small surface areas of the perovskites synthesized by traditional sol-gel methods lead to low utilization of catalytic sites, which gives rise to poor Li-O2 batteries performance and restricts their application. Herein, a hierarchical mesporous/macroporous perovskite La0.5Sr0.5CoO3-x (HPN-LSC) nanotube is developed to promote its application in Li-O2 batteries. The HPN-LSC nanotubes were synthesized via electrospinning technique followed by postannealing. The as-prepared HPN-LSC catalyst exhibits outstanding intrinsic ORR and OER catalytic activity. The HPN-LSC/KB electrode displays excellent performance toward both discharge and charge processes for Li-O2 batteries, which enhances the reversibility, the round-trip efficiency, and the capacity of resultant batteries. The synergy of high catalytic activity and hierarchical mesoporous/macroporous nanotubular structure results in the Li-O2 batteries with good rate capability and excellent cycle stability of sustaining 50 cycles at a current density of 0.1 mA cm(-2) with an upper-limit capacity of 500 mAh g(-1). The results will benefit for the future development of high-performance Li-O2 batteries using hierarchical mesoporous/macroporous nanostructured perovskite-type catalysts.

Toward enhanced hydrogen generation from water using oxygen permeating LCF membranes

Hydrogen production from water thermolysis can be enhanced by the use of perovskite-type mixed ionic and electronic conducting (MIEC) membranes, through which oxygen permeation is driven by a chemical potential gradient. In this work, water thermolysis experiments were performed using 0.9 mm thick La0.9Ca0.1FeO3-δ (LCF-91) perovskite membranes at 990 °C in a lab-scale button-cell reactor. We examined the effects of the operating conditions such as the gas species concentrations and flow rates on the feed and sweep sides on the water thermolysis rate and oxygen flux. A single step reaction mechanism is proposed for surface reactions, and three-resistance permeation models are derived. Results show that water thermolysis is facilitated by the LCF-91 membrane especially when a fuel is added to the sweep gas. Increasing the gas flow rate and water concentration on the feed side or the hydrogen concentration on the sweep side enhances the hydrogen production rate. In this work, hydrogen is used as the fuel by construction, so that a single-step surface reaction mechanism can be developed and water thermolysis rate parameters can be derived. Both surface reaction rate parameters for oxygen incorporation/dissociation and hydrogen-oxygen reactions are fitted at 990 °C. We compare the oxygen fluxes in water thermolysis and air separation experiments, and identify different limiting steps in the processes involving various oxygen sources and sweep gases for this 0.9 mm thick LCF-91 membrane. In the air feed-inert sweep case, the bulk diffusion and sweep side surface reaction are the two limiting steps. In the water feed-inert sweep case, surface reaction on the feed side dominates the oxygen permeation process. Yet in the water feed-fuel sweep case, surface reactions on both the feed and sweep sides are rate determining when hydrogen concentration in the sweep side is in the range of 1-5 vol%. Furthermore, long term studies show that the surface morphology changes and silica impurities have little impact on the oxygen flux for either water thermolysis or air separation.