High Performance Nano-Ceria Electrodes for Solid Oxide Cells

In solid oxide electrochemical cells, the conventional Ni-based fuel-electrodes provide high electrocatalytic activity but they are often a major source of long-term performance degradation due to carbon deposition, poisoning of reaction sites, Ni mobility, etc. Doped-ceria is a promising mixed ionic-electronic conducting oxide that could solve these issues if it can be integrated into an appropriate electrode structure. Two new approaches to obtain high-performance nanostructured doped-ceria electrodes are highlighted. The first is an infiltration-based architecture with Ce0.8Pr0.2O2-δ forming the active surfaces on a porous backbone with embedded electronic current collector material, yielding one of the highest performances reported for an electrode that operates either on fuel or oxidant. The second is a nano-Ce0.9Gd0.1O2-δ thin film prepared by spin-coating, which provides an unprecedented electrode polarization resistance of ~0.01 Ω cm2 at 650 °C in H2/H2O. These results demonstrate that nano-ceria has the ability to achieve higher performance than Ni-based electrodes and show that the main challenge is obtaining sufficient electronic current collection without adding too much inactive material.</jats:p

Exploring the Processing of Tubular Chromite- and Zirconia-Based Oxygen Transport Membranes

Tubular oxygen transport membranes (OTMs) that can be directly integrated in high temperature processes have a large potential to reduce CO2 emissions. However, the challenging processing of these multilayered tubes, combined with strict material stability requirements, has so far hindered such a direct integration. We have investigated if a porous support based on (Y2O3)0.03(ZrO2)0.97 (3YSZ) with a dense composite oxygen membrane consisting of (Y2O3)0.01(Sc2O3)0.10(ZrO2)0.89 (10Sc1YSZ) as an ionic conductor and LaCr0.85Cu0.10Ni0.05O3−δ (LCCN) as an electronic conductor could be fabricated as a tubular component, since these materials would provide outstanding chemical and mechanical stability. Tubular components were made by extrusion, dip coating, and co-sintering, and their chemical and mechanical integrity was evaluated. Sufficient gas permeability (≥10−14 m2) and mechanical strength (≥50 MPa) were achieved with extruded 3YSZ porous support tubes. The high co-sintering temperature required to densify the 10ScYSZ/LCCN membrane on the porous support, however, causes challenges related to the evaporation of chromium from the membrane. This chemical degradation caused loss of the LCCN electronic conducting phase and the formation of secondary lanthanum zirconate compounds and fractures. LCCN is therefore not suitable as the electronic conductor in a tubular OTM, unless means to lower the sintering temperature and reduce the chromium evaporation are found that are applicable to the large-scale fabrication of tubular components

Partial oxidation of biomass gasification tar with oxygen transport membranes

Dual phase oxygen transport membranes were directly integrated into the producer gas stream of a low temperature circulating fluidized bed (LT-CFB) gasifier for partial oxidation of tar. Ce0.9Gd0.1O1.95–La0.6Sr0.4FeO3-d composite membranes were prepared by extrusion and dip-coating, co-sintered and infiltrated with electro-catalysts. These were investigated in two different set-ups: i) a membrane test rig, and ii) a partial oxidation testing unit connected to a biomass gasifier. The stability and performance of the membrane were tested in two different gas-streams; i) H2 and ii) producer gas. An oxygen flux of 1.5 Nml∙cm−2∙min−1 was measured in an air/H2 gradient at 850 °C through a 10 cm long membrane with a diameter of 10 mm, whereas a lower oxygen flux of 0.5 Nml∙cm−2∙min−1 was measured for the air/producer gas case. The producer gas contained ca. 2000 mg Nm−3 of primary tar. Analysis of the gas and the tar composition at the output of the membrane unit demonstrated that it contributed to the partial oxidation of the primary tar, resulting in a twofold increase of H2, CH4 and CO in the producer gas. This successful integration of oxygen transport membranes demonstrated that these membranes can reduce the tar content in producer gas from biomass gasifiers.This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement no.101022432 (FLEXSNG project) and from “Highly Flexible Energy Production by Oxy-Fired Biomass Gasification (HighFlex)” EUDP grant No.: 64018–0028 (previously 12403).Peer reviewe

Stable, asymmetric, tubular oxygen transport membranes of (Sc₂O₃)_0.10(Y₂O₃)_0.01(ZrO₂)_0.89 – LaCr_0.85Cu_0.10Ni_0.05O_3-δ

Oxygen transport membranes have the potential to deliver pure and cheap oxygen to chemical reactors, combustors, gasifiers etc., given that geometry, microstructure and material properties are optimized. This work demonstrates the first successful preparation of dual-phase tubular, asymmetric oxygen transport membranes consisting of a new electronic conductor LaCr0.85Cu0.10Ni0.05O3-δ mixed with (Sc2O3)0.10(Y2O3)0.01(ZrO2)0.89 as ionic conductor. Challenges related to Cr-volatility were overcome by using Fe2O3 as a sintering aid. The sintering aid decreased mismatches in shrinkage and thermal expansion between the four layers in the asymmetric membrane and decreased the sintering temperature such that the Cr-volatility was suppressed. The membranes reached an oxygen flux of 0.28 ml∙min−1∙cm−2 in an air/N2 atmosphere at 950 °C. Furthermore, the membranes showed a stable oxygen flux after exposure to different atmospheres, including air/CO2 and air/H2 gradients. The successful fabrication of stable, asymmetric, tubular membranes opens the possibility for future integration in syngas or oxy-combustion applications

A review on dual-phase oxygen transport membranes: from fundamentals to commercial deployment

Oxygen transport membranes (OTMs) are a promising alternative to cryogenic air separation (ASU) or pressure swing adsorption (PSA) for oxygen production. Using these ceramic membranes allows producing high purity oxygen on various scales in a continuous single-step process, at lower costs and power consumption, making it an advantageous technique for oxy-combustion in connection with carbon capture and delocalized oxygen production on a small scale. Moreover, their use in membrane reactors, directly utilizing the permeating oxygen in chemical reactions towards green chemistry, is an emerging research field. Especially dual-phase OTMs, where the membrane consists of a composite of a stable ionic conductor and a stable electronic conductor, are of high interest, because they can overcome the disadvantages of single-phase membranes like low chemical and mechanical stability at elevated temperatures and under harsh operation conditions. However, despite the progress in the development of dual-phase OTMs over the last years, and their potential applications in classic and emerging fields, challenges preventing their large-scale employment remain. This review aims to guide new studies that will promote the development and upscaling of dual-phase OTMs. Recent developments, current opportunities and challenges, and future directions of research are thoroughly discussed. Through this review paper, information about the basic working principle, properties, performance and current application in industry of dual-phase OTM membranes can be comprehended. Next to material properties, preparative methods and manufacturing are in focus, intending to accelerate development and upscaling of new materials and components. Furthermore, existing challenges and research strategies to overcome these are discussed, and focus areas and prospects of future application areas are suggested

A review on dual-phase oxygen transport membranes: from fundamentals to commercial deployment

Oxygen transport membranes (OTMs) are a promising alternative to cryogenic air separation (ASU) or pressure swing adsorption (PSA) for oxygen production. Using these ceramic membranes allows producing high purity oxygen on various scales in a continuous single-step process, at lower costs and power consumption, making it an advantageous technique for oxy-combustion in connection with carbon capture and delocalized oxygen production on a small scale. Moreover, their use in membrane reactors, directly utilizing the permeating oxygen in chemical reactions towards green chemistry, is an emerging research field. Especially dual-phase OTMs, where the membrane consists of a composite of a stable ionic conductor and a stable electronic conductor, are of high interest, because they can overcome the disadvantages of single-phase membranes like low chemical and mechanical stability at elevated temperatures and under harsh operation conditions. However, despite the progress in the development of dual-phase OTMs over the last years, and their potential applications in classic and emerging fields, challenges preventing their large-scale employment remain. This review aims to guide new studies that will promote the development and upscaling of dual-phase OTMs. Recent developments, current opportunities and challenges, and future directions of research are thoroughly discussed. Through this review paper, information about the basic working principle, properties, performance and current application in industry of dual-phase OTM membranes can be comprehended. Next to material properties, preparative methods and manufacturing are in focus, intending to accelerate development and upscaling of new materials and components. Furthermore, existing challenges and research strategies to overcome these are discussed, and focus areas and prospects of future application areas are suggested