Research Trends in Development of Highly Active Single Metal Oxide Catalyst for Oxidative Coupling of Methane

The conversion of methane to a value-added chemical is important for methane utilization and industrial demand for primary chemicals. Oxidative coupling of methane (OCM) to C2 hydrocarbons is one of the most attractive ways to use natural gas. However, it is difficult to obtain higher C2 yield in classic OCM reaction due to a favorable COx formation. Regarding this, various catalysts for OCM have been studied to fulfill desirable C2 yields. In this review, we briefly overview the single metal oxide types of OCM catalysts (alkaline-earth metal oxides and rare-earth metal oxides) and highlight the characteristics of catalysts in OCM reaction such as methane activation, surface basicity and lattice oxygen.

Flash Light Sintered Lanthanum Strontium Cobalt Ferrite(LSCF) Electrode for High Performance IT-SOFCs

The high temperature(900oC~) thermal sintering process is necessary to fabricate the Solid oxide fuel cells(SOFCs). However, the chemical reaction has occurred between solid oxide material components, electrode and electrolyte. In the case of lanthanum strontium cobalt ferrite (La0.6Sr0.4Co0.2Fe0.8O3-δ, LSCF) electrode, the SrZrO3(SZO) secondary phase is produced at the electrolyte interface even when using the gadolinium doped ceria(GDC) buffer layer for blocking the strontium and zirconium diffusion. The SZO layer hinders the oxygen ion transfer and deteriorates fuel cell performance. By using a novel flash light sintering(FLS) method, we have successfully solved the problem of secondary phase formation in the conventional high temperature thermal sintering process. The microstructure and thickness of the LSCF electrode are analyzed using a field emission scanning electron microscope(FE-SEM). The strontium diffusion and secondary phase are confirmed by X-ray diffraction (XRD), energy dispersive spectrometer method of SEM, TEM (SEM-, TEM-EDS). The NiO-YSZ anode supported LSCF cathode cells are adopted for electro chemical analysis which is measured at 750oC. The maximum power density of the thermal sintered LSCF cathode at 1050oC is 699.6mW/cm2, while that of the flash light sintered LSCF cathode is 711.6mW/cm2. This result proves that the electrode was successfully sintered without a secondary phase using flash light sintering.

Recent Advances in High Temperature Electrolysis Cells using LaGaO3-based Electrolyte

High temperature electrolysis is a promising option for carbon-free hydrogen production and huge energy storage with high energy conversion efficiencies from renewable and nuclear resources. Over the past few decades, yttria-stabilized zirconia (YSZ) based ion conductor has been widely used as a solid electrolyte in solid oxide electrolysis cells (SOECs). However, its high operation temperature and lower conductivity in the appropriate temperature range for solid electrochemical devices were major drawbacks. Regarding improving ionic-conducting electrolytes, several groups have contributed significantly to developing and applying LaGaO3 based perovskite as a superior ionic conductor. La(Sr)Ga(Mg)O3 (LSGM) electrolyte was successfully validated for intermediate-temperature solid oxide fuel cells (SOFCs) but was rarely conducted on SOECs for its high efficient electrolysis performance. Their lower mechanical strengths or higher reactivity with electrode compared with the YSZ electrolysis cells, which make it difficult to choose compatible materials, remain major challenges. In this field, SOECs have attracted a great attention in the last few years, as they offer significant power and higher efficiencies compared to conventional YSZ based electrolysers. Herein, SOECs using LSGM based electrolyte, their applications, high performance, and their issues will be reviewed.

Application of Electrochemical Deposition in Solid Oxide Fuel Cell Technology

This review paper describes the principle of electrochemical deposition and introduces recent studies applying it to the electrode fabrication of a solid oxide fuel cell (SOFC), a next-generation energy conversion device. Electrochemical deposition can easily control the structure and morphology of the deposition layer according to the applied bias/time/temperature, etc., and the process is very simple and possible even at low temperatures. In addition, deposition of cerium-based oxides, which are the representative ion-conductors or mixed-conductors widely used for SOFCs, is also possible <i>via</i> electrochemical deposition. To elucidate the effectiveness/novelty of electrochemical deposition, we present examples of the application of electrochemical deposition in SOFCs. Moreover, examples of using this method to study the properties of a material and/or to fabricate perovskite oxide-based electrodes are included.

Progress in Metal-supported Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) have been attracting much attention as alternative energy conversion devices due to their high energy conversion efficiency and fuel flexibility. In current SOFCs, Ni-based Cermet anode, solid oxide electrolyte and ceramic cathode have been used. Since all components are ceramic-based materials, there is a problem in that mechanical strength and durability against thermal shock. In order to solve this problem, metal-supported solid oxide fuel cells have designed. Metal-supported solid oxide fuel cells provide significant advantages such as low materials cost, ruggedness, and tolerance to rapid thermal cycling and redox cycling. This paper review the types of metal supports used in metal-based solid oxide fuel cells and the advantages and disadvantages of each metal support.

Electrochemical Evaluation of Layered Perovskite YBa0.5Sr0.5Co1.5Fe0.5O5+δ Cathode as a Triple Ionic and Electronic Conductor for Protonic Ceramic Fuel Cells

Protonic ceramic fuel cells (PCFCs) have receiving huge attention as a promising energy conversion device because of their high conversion efficiency, lack of fuel dilution, and high ionic conductivity at intermediate temperature regime (400 ∼ 600 oC). Although this fuel cell system can effectively solve the main obstacle for the commercialization of conventional solid oxide fuel cells, electrochemical performance is currently limited by the cathodic polarization due to insufficient catalytic activity. To overcome this issue, layered perovskite materials, PrBa0.5Sr0.5Co1.5Fe0.5O5+δ, have been discovered as triple ionic and electronic conductor, which enables to simultaneously conduct H+/O2-/e-. Despite great advantages, there is large gap in the thermal expansion coefficient (TEC) between the cathode and electrolyte. Herein, we developed a new triple conducting cathode material, YBa0.5Sr0.5Co1.5Fe0.5O5+δ (YBSCF) to minimize TEC while maintaining the high electro-catalytic activity with excellent hydration properties. Structural analysis, hydration properties, and electrochemical performances of YBSCF cathode were investigated. In particular, the peak power density of YBSCF cathode based on BaZr0.4Ce0.4Y0.1Yb0.1O3-δ (BZCYYb4411) electrolyte attained 0.702 W cm-2 at 600 oC. Moreover, power output is fairly stable for 300 h without observable degradation by applying a constant voltage of 0.7 V at 600 oC.

Development of Ammonia Fueled Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) can generate electricity through an electrochemical conversion of the chemical energy of fuels including hydrogen, hydrocarbons, and biogas because of high operation temperatures. Ammonia has recently been considered as a promising hydrogen carrier that is relatively convenient to store and transport and can be decomposed into hydrogen and nitrogen with no carbon emission via catalytic cracking. Thus, much effort has been made to utilize ammonia as a clean fuel to SOFCs for power generation at high efficiency. This review is aiming at delivering the current progress of developing high temperature ceramic fuel cells fed with ammonia, particularly more focused on the achievements of a direct ammonia fueled SOFC (DA-SOFC) to shed light on the challenges of degrading the performance and durability. The problems are primarily attributed to a lack of rational catalysts, thermal imbalance, and the evolution of nitrides on the components including the Ni based anode, Ni mesh as current collector, and stainless steels of metallic interconnect that are exposed to the ammonia fuel environment incurring microstructural deformations and electrical and electrochemical deteriorations. Lastly, strategic pathways to overcome the inadequate performance and the instability are suggested to accomplish a commercialization of DA-SOFCs.

A Review of Electrochemical Cells with Geometrically Well-defined Interfaces for Solid Oxide Fuel Cell Anodes

A solid oxide fuel cell (SOFC) is a high-temperature (above 750℃) energy conversion device that generates electricity with high efficiency and low CO2 emission. It is essential to develop high-activity electrodes for its commercialization by lowering the operating temperature to below 700℃. Understanding the electrode reaction kinetics can provide fundamental insights for the rational design of high-performance electrodes. However, the three-dimensional porous microstructures of the SOFC electrodes make it difficult to analyze the reaction processes precisely. To overcome this issue associated with the conventional electrodes, the model electrodes with geometrically well-defined interfaces have been widely employed. In this paper, focusing on the SOFC anodes, the fabrication techniques, cell types, analysis tools, and the modeling studies in the literature will be reviewed.

Recent Advances in High Temperature Electrolysis Cells using LaGaO3-based Electrolyte

High temperature electrolysis is a promising option for carbon-free hydrogen production and huge energy storage with high energy conversion efficiencies from renewable and nuclear resources. Over the past few decades, yttria-stabilized zirconia (YSZ) based ion conductor has been widely used as a solid electrolyte in solid oxide electrolysis cells (SOECs). However, its high operation temperature and lower conductivity in the appropriate temperature range for solid electrochemical devices were major drawbacks. Regarding improving ionic-conducting electrolytes, several groups have contributed significantly to developing and applying LaGaO3 based perovskite as a superior ionic conductor. La(Sr)Ga(Mg)O3 (LSGM) electrolyte was successfully validated for intermediate-temperature solid oxide fuel cells (SOFCs) but was rarely conducted on SOECs for its high efficient electrolysis performance. Their lower mechanical strengths or higher reactivity with electrode compared with the YSZ electrolysis cells, which make it difficult to choose compatible materials, remain major challenges. In this field, SOECs have attracted a great attention in the last few years, as they offer significant power and higher efficiencies compared to conventional YSZ based electrolysers. Herein, SOECs using LSGM based electrolyte, their applications, high performance, and their issues will be reviewed.

Giant Grain Growth in (K,Na)NbO3 Ceramics

In this manuscript, an interesting phenomenon is reported. It has been reported that the growth of single crystals is observed in donor-doped (K,Na)NbO3 (KNN)-based ceramics. It is very interesting that the growth happens without the addition of a seed. The growth of huge grains (single crystal, approximately 30 mm,) occurs due to the abnormal grain growth (AGG) in KNN-based ceramics. In the AGG compositions, moreover, the seed plates can be synthesized by not topochemical reaction but simple molten salt synthesis (SMSS) which is a simple-and-cheap process. They can be a good candidate for the seeds at reactive templated grain growth (RTGG) or templated grain growth (TGG) process.