Preparation and hydrogen permeation of BaCe0.95Nd0.05O3−δ membranes

Perovskite Membranes: Advancements and Challenges in Gas Separation, Production, and Capture

Perovskite membranes have gained considerable attention in gas separation and production due to their unique properties such as high selectivity and permeability towards various gases. These membranes are composed of perovskite oxides, which have a crystalline structure that can be tailored to enhance gas separation performance. In oxygen enrichment, perovskite membranes are employed to separate oxygen from air, which is then utilized in a variety of applications such as combustion and medical devices. Moreover, perovskite membranes are investigated for carbon capture applications to reduce greenhouse gas emissions. Further, perovskite membranes are employed in hydrogen production, where they aid in the separation of hydrogen from other gases such as methane and carbon dioxide. This process is essential in the production of clean hydrogen fuel for various applications such as fuel cells and transportation. This paper provides a review on the utilization and role of perovskite membranes in various gas applications, including oxygen enrichment, carbon capture, and hydrogen production.

Ion-Conducting Ceramic Membrane Reactors for the Conversion of Chemicals

Ion-conducting ceramic membranes, such as mixed oxygen ionic and electronic conducting (MIEC) membranes and mixed proton-electron conducting (MPEC) membranes, have the potential for absolute selectivity for specific gases at high temperatures. By utilizing these membranes in membrane reactors, it is possible to combine reaction and separation processes into one unit, leading to a reduction in by-product formation and enabling the use of thermal effects to achieve efficient and sustainable chemical production. As a result, membrane reactors show great promise in the production of various chemicals and fuels. This paper provides an overview of recent developments in dense ceramic catalytic membrane reactors and their potential for chemical production. This review covers different types of membrane reactors and their principles, advantages, disadvantages, and key issues. The paper also discusses the configuration and design of catalytic membrane reactors. Finally, the paper offers insights into the challenges of scaling up membrane reactors from experimental stages to practical applications.

Hydrogen Purification through a Highly Stable Dual-Phase Oxygen-Permeable Membrane

Using oxygen permeable membranes (OPMs) to upgrade low‐purity hydrogen is a promising concept for high‐purity H₂ production. At high temperatures, water dissociates into hydrogen and oxygen. The oxygen permeates through OPM and oxidizes hydrogen in a waste stream on the other side of the membrane. Pure hydrogen can be obtained on the water‐splitting side after condensation. However, the existing Co‐ and Fe‐based OPMs are chemically instable as a result of the over‐reduction of Co and Fe ions under reducing atmospheres. Herein, a dual‐phase membrane Ce_0.9Pr_0.1O_2−δ‐Pr_0.1Sr_0.9Mg_0.1Ti_0.9O_3−δ (CPO‐PSM‐Ti) with excellent chemical stability and mixed oxygen ionic‐electronic conductivity under reducing atmospheres was developed for H₂ purification. An acceptable H₂ production rate of 0.52 mL min⁻¹ cm⁻² is achieved at 940 °C. No obvious degradation during 180 h of operation indicates the robust stability of CPO‐PSM‐Ti membrane. The proven mixed conductivity and excellent stability of CPO‐PSM‐Ti give prospective advantages over existing OPMs for upgrading low‐purity hydrogen.

Catalytic mixed conducting ceramic membrane reactors for methane conversion

Schematic of catalytic mixed conducting ceramic membrane reactors for various reactions: (a) O₂ permeable ceramic membrane reactor; (b) H₂ permeable ceramic membrane reactor; (c) CO₂ permeable ceramic membrane reactor.

Effect of strontium on Nd doped Ba1-x Sr x Ce0.65Zr0.25Nd0.1O3-δ proton conductor as an electrolyte for solid oxide fuel cells

This paper investigated the Sr doping effect on the microstructure, chemical stability, and conductivity of Ba_1−xSr_xCe_0.65Zr_0.25Nd_0.1O_3−δ (0 ⩽ x ⩽ 0.2) electrolyte prepared by sol-gel method. The lattice constants and unit cell volumes were found to decrease as Sr atomic percentage increased in accordance with the Vegard law, confirming the formation of solid solution. Incorporation of Sr into the composition resulted in smaller grains besides suppressing the formation of secondary phases of SrCeO₃. Among the synthesized samples BaCe_0.65Zr_0.25Nd_0.1O_3−δ pellet with orthorhombic structure showed highest conductivity with a value of 2.08 × 10⁻³ S/cm(dry air) and 2.12 × 10⁻³ S/cm (wet air with 3% relative humidity) at 500 °C due to its smaller lattice volume, larger grain size, and lower activation energy that led to excessive increase in conductivity. Ba_0.8Sr_0.2Ce_0.65Zr_0.25Nd_0.1O_3−δ recorded lower conductivity with a value of 4.62 × 10⁻⁴ S/cm (dry air) and 4.83 × 10⁻⁴ S/cm (wet air with 3% relative humidity) at 500 °C than Sr undoped but exhibited better chemical stability when exposed to air and H₂O atmospheres. Comparisons with the literature showed the importance of the synthesis method on the properties of the powders. Hence this composition can be a promising electrolyte if all the values such as sintering temperature, Sr dopant concentration, and time are proportionally controlled.

Hydrogen separation through tailored dual phase membranes with nominal composition BaCe0.8Eu0.2O3-δ:Ce0.8Y0.2O2-δ at intermediate temperatures

Hydrogen permeation membranes are a key element in improving the energy conversion efficiency and decreasing the greenhouse gas emissions from energy generation. The scientific community faces the challenge of identifying and optimizing stable and effective ceramic materials for H₂ separation membranes at elevated temperature (400-800 °C) for industrial separations and intensified catalytic reactors. As such, composite materials with nominal composition BaCe_0.8Eu_0.2O_3-δ:Ce_0.8Y_0.2O_2-δ revealed unprecedented H₂ permeation levels of 0.4 to 0.61 mL·min^-1·cm^-2 at 700 °C measured on 500 μm-thick-specimen. A detailed structural and phase study revealed single phase perovskite and fluorite starting materials synthesized via the conventional ceramic route. Strong tendency of Eu to migrate from the perovskite to the fluorite phase was observed at sintering temperature, leading to significant Eu depletion of the proton conducing BaCe_0.8Eu_0.2O_3-δ phase. Composite microstructure was examined prior and after a variety of functional tests, including electrical conductivity, H₂-permeation and stability in CO₂ containing atmospheres at elevated temperatures, revealing stable material without morphological and structural changes, with segregation-free interfaces and no further diffusive effects between the constituting phases. In this context, dual phase material based on BaCe_0.8Eu_0.2O_3-δ:Ce_0.8Y_0.2O_2-δ represents a very promising candidate for H₂ separating membrane in energy- and environmentally-related applications.

Unprecedented CO2-promoted hydrogen permeation in Ni-BaZr0.1Ce0.7Y0.1Yb0.1O(3-δ) membrane

Conventional Ni-BaCeO3-based membranes possess high hydrogen permeation flux but suffer serious flux degradation in CO2-containing atmosphere because of the formation of BaCO3 insulating layer. In this work, we report a novel Ni-BaZr0.1Ce0.7Y0.1Yb0.1O(3-δ) (Ni-BZCYYb) membrane, capable of both high hydrogen permeation flux and stable performance in CO2-containing atmosphere at 900 °C. Most importantly, the flux is found to be promoted rather than being diminished by CO2 normally observed for other high temperature proton conductors. The flux enhancement in Ni-BZCYYb membrane is attributed to the increase of moisture content in feed gas. When CO2 is introduced, the reverse water-gas shift reaction takes place generating H2O and CO. This work demonstrates that CO2 can be beneficial rather than detrimental for hydrogen permeation membranes that possess high chemical stability.