Advances in solid oxide fuel cell electrolyte fabrication by pulsed laser deposition

Solid oxide fuel cells (SOFCs) are emerging as energy conversion devices for large-scale electrical power generation because of their high energy conversion efficiency, excellent ability to minimize air pollution, and high fuel flexibility. In this context, this critical review has focussed on the recent advancements in developing a suitable electrolyte for SOFCs which has been required for the commercialization of SOFC technology after emphasizing the literature from the prior studies. In particular, the significant developments in the field of solid oxide electrolytes for SOFCs, particularly zirconia- and ceria-based electrolytes, have been highlighted as important advancements toward the production of sustainable and clean energy. It has been reported that among various electrolyte materials, zirconia-based electrolytes have the potential to be utilized as the electrolyte in SOFC because of their high thermal stability, non-reducing nature, and high mechanical strength, along with acceptable oxygen ion conductivity. However, some studies have proved that the zirconia-based electrolytes are not suitable for low and intermediate-temperature working conditions because of their poor ionic conductivity to below 850°C. On the other hand, ceria-based electrolytes are being investigated at a rapid pace as electrolytes for intermediate and low-temperature SOFCs due to their higher oxygen ion conductivity with good electrode compatibility, especially at lower temperatures than stabilized zirconia. In addition, the most emerging advancements in electrolyte materials have demonstrated that the intermediate temperature SOFCs as next-generation energy conversion technology have great potential for innumerable prospective applications.

The development and interest in environmentally friendly cars nowadays present new challenges to the lithium-ion batteries. With the safety problems caused by the liquid electrolyte in conventional batteries, the development of new electrolytes is becoming increasingly urgent. Based on the existing literature, this paper discusses the following: (1) the advantages and disadvantages of solid-state electrolytes; (2) Requirements for solid electrolytes; (3) Classification and characteristics of solid electrolytes; (4) Properties of different types of electrolytes; (5) Future application and research direction. Performance and possible applications of different solid-state electrolytes are presented in this paper. Specifically, it is found that inorganic solid electrolytes are the best in ion transference number, making them suitable for quick charging batteries. Polymer-based solid electrolytes perform better at electrochemical window, so they can be used to enhance the energy density of batteries. Polyethylene glycol (PEG) based composite solid electrolytes and sulfide solid electrolytes have the highest ionic conductivity, so they are optimum materials for high-rate performance batteries.

1.Introduction Solid oxide fuel cells (SOFCs) have received much attention as promising electrochemical power generation devices because of their high electrical efficiency and environment adaptability. Development of SOFCs is now focused on lowering the operating temperature from the conventional range of 750-900°C to an intermediate range of 500-700ºC, allowing a wider range of materials for SOFC components and improvement of thermal reliability. Preparing the Yttlia Stabilized Zirconia (YSZ) and Gadolinia-doped ceria (GDC)) bilayer electrolytes are effective for reducing operating temperature [1]. In the present work, NiO-YSZ anode supported cells with YSZ/GDC bilayer electrolytes and (La,Sr) (Co,Fe) O3 (LSCF) thin film cathodes were fabricated by pulsed laser deposition (PLD) and screen printing. However, one thermal cycle test of a cell between 200°C and 600°C, with heating and cooling rates of 400°C /h, resulted in detachment of the LSCF thin film and thus reduced durability. To improve the adhesion between the LSCF and GDC, (La,Sr)CoO3(LSC), nano particles were deposited on the GDC thin films by PLD. This step was expected to increase contact area between electrolyte and cathode. We investigated the influence of the LSC nano particle on thermal reliability and I-V characteristic of SOFCs. 2.Experimental Details NiO-YSZ cermet (NiO:YSZ＝60:40 wt%, 500 μm thick) was used as the anode substrate, YSZ (8 mol% Y2O3) and GDC (10 mol% GdO2) as electrolyte materials, and La0.6Sr0.4Co0.2Fe0.8 (LSCF) and La0.6Sr0.4Co (LSC) as cathode materials. YSZ (8 μm thick) and LSCF (30 μm thick) films were prepared by screen printing and GDC (3 μm thick) was deposited by PLD. Two sets of unit cells were prepared: one set was with LSC nano particles deposited between GDC and LSCF thin films by PLD (NiO-YSZ / YSZ / GDC / LSC particle / LSCF) and the other set was without LSC nano particles (NiO-YSZ / YSZ / GDC / LSCF).Thermal cycle test between 200 and 600°C with heating and cooling rates of 400° C /h were performed. Power densities and I-V characteristics were measured. 3.Results (a) Deposition of LSC nano particles by PLD on the GDC thin film. Figure 1 shows a scanning electron microscopy image of the surface of a GDC thin film. Many LSC nano particles (50-nm diameter) were deposited on the dense GDC thin film by PLD, which increased the area of contact between the GDC and LSCF thin films. (b) Thermal cycle test of NiO-YSZ anode supported cells with or without LSC nano particles. Two types of unit cells, (1) NiO-YSZ / YSZ / GDC / LSC particle / LSCF and (2) NiO-YSZ / YSZ / GDC / LSCF were prepared by screen printing and PLD. Photographs of unit cells after one thermal cycle are shown in Fig. 2. It is evident that adding the LSC nano particles succeeded in suppressing detachment of the LSCF thin film. Spike effect resulted in high adhesion between LSCF and GDC. The unit cell with LSC nano particles survived 50 thermal cycles and yielded higher thermal reliability. (c) I-V characteristics of NiO-YSZ anode supported cells with or without LSC nano particles. Figure 3 shows the I-V characteristics of unit cells with and without LSC nano particles. The maximum power densities of unit cells with or without LSC nano particles were 0.5 and 0.3 W·cm-2, respectively. Cell performances were found to be better when LSC nano particles were deposited, because of increase in reactive sites.[1] T. Mukai et al., Journal of Fuel Cell Science and Technology , 10(2013) 061006-1-6.

Thin films are commonly utilized in industries such as electronics, packaging, decoration, and protection. The two primary techniques for thin‐film deposition include physical vapor deposition (PVD) and chemical vapor deposition (CVD). The selection and application of a particular technique depends on the desired properties of thin films. For example, for electronic applications where via filling is a requirement, preference is for the CVD process where gaseous precursor finds its way to all spaces, forming a uniform thin film on the whole topography. PVD techniques have limitation that the substrate surface has to be in the line of sight of the incoming flux. Contoured surfaces require special source and substrate manipulation for conformal coatings. Likewise, where large flat surface area coverage is needed, like thin films on decorative window glass, a simpler process such as PVD, both as evaporation and sputtering, is preferred over CVD. This article describes PVD and CVD techniques and their multiple variants. PVD processes, evaporation, sputtering, and pulsed laser deposition (PLD) with their variants, ion plating and high‐power impulse magnetron sputtering (HIPIMS), form the first part of the article, whereas the second part contains descriptions of CVD processes, including metalorganic chemical vapor deposition (MOCVD) and plasma‐assisted (or enhanced) chemical vapor deposition (PACVD). Notably absent in this article are molecular beam epitaxy (MBE), a PVD process and atomic layer epitaxy (ALE), a CVD process. These are very controlled deposition processes and require sophisticated control hardware. It is this sophistication that requires MBE and ALD to be dealt separately and, therefore, not included in this article.

Solid oxide fuel cells (SOFCs) have aroused worldwide attention for their high conversion efficiency, zero emissions, and fuel flexibility. Generally, a SOFC consists of an anode, a cathode and a electrolyte. The electrolytes usually exert a crucial role in the performance of SOFCs. The normal electrolyte materials could be generally divided into two subclasses: oxygen ion and proton-conducting electrolyte ones, based on their different types of conduction mechanisms. In this chapter, we describe the requirements for the materials as the electrolytes of SOFCs and the recent developments of oxygen-ion conducting electrolyte, proton-conducting electrolyte and dual-phase composite electrolyte materials. Major attention is paid to the influences of structures, preparation and modified methods on the ion conduction properties of fluorite and perovskite electrolyte materials of SOFCs.

Matrix shaped pulsed laser deposition: New approach to large area and homogeneous deposition

We have reported the ultimate performance level that the anode-supported solid oxide fuel cell (SOFC) can reach by employing thin-film electrolytes and nano-structure electrodes, without drastically changing the component materials. Based on the platform named as multi-scale-architectured thin-film SOFC (TF-SOFC), thin-film electrolytes of thickness less than 1 micron and electrodes with particle size in nm scale are successfully realized on NiO-YSZ anode supports, and a peak power density exceeding 500 mWcm-2 at 500 oC is obtained. Although this approach proves the potential of the thin-film technology to significantly improve the low-temperature performance of the SOFC, it is highly questionable that this platform can be transferred to the commercial sector because pulsed laser deposition (PLD) is employed to fabricate the cells. PLD is the best thin-film deposition research tool for the oxide with complex composition and has a high deposition rate, which is tremedous advantages for the thin film components in the TF-SOFC. Nevertheless, PLD has a small deposition area which cannot be larger than several cm by several cm in general, which is the most critical disadvantage of PLD to be employed as a commerciallization processing technique. Therefore, to be employed in the commercial sector, it is the prerequisite that the multi-scale-architectured TF-SOFC should be realized by commercially viable techniques other than PLD. In this regard, the present study deals with the realization of the same platform by using other technique, specifically sputtering. Several key issues, such as nano-composite deposition, stoichiometry transfer, crystallinity of the thin films, etc., will be identified and the possible solutions to resolve these issues in sputtering will be suggested. A larger area (~ 5 cm by 5 cm) TF-SOFC using a 2-inch sputtering system will be fabricated to check the fesibility and its chracteristics will be compared with that of the cell fabricated using PLD.

Fuel cells could play an important role in the ongoing energy transition by providing clean and efficient energy conversion. Although the solid oxide fuel cell (SOFC) technology is a potential alternative for large-scale applications, its commercialization is limited by its electrolyte materials and has not yet been realized. Progress on new functional semiconductor-ionic materials (SIMs) and the fundamentals of SOFCs will provide new paths for their research and development. Herein, we discuss the nanoscale electrochemistry phenomena of SIMs in the context of new concepts for advanced SOFCs. A traditional SOFC consists of a three-layer anode/electrolyte/cathode structure, where the physically separated electrolyte layer is indispensable for ion transport to support the redox reaction and prevent the occurrence of short circuiting. A novel nano-SOFC concept is proposed to replace the traditional electrolyte by a SIM or semiconductor membrane and it can deliver superior performance, even at a lower temperature range (< 500 °C). The scientific basis and prospects of this new technological approach are presented and discussed.

At present, the solid oxide fuel cell (SOFC) is attracting much attention because it possesses the highest power generation efficiency among many types of fuel cell, and SOFC emits only water that does not harm the environment. Recently, the electrolyte structure for SOFC has been processed into various forms to increase the efficiency of SOFC. In this work, we tried to improve the performance of SOFC by changing the mesostructure on the interfaces between the electrolyte and electrodes. This hundred-micrometer-scaled mesostructure has been proposed to increase the reaction on the interfaces. However, there has been no effective method of fabricating the cells with the microstructure along the interfaces. We have already proposed the micro powder imprint (µPI) method to create fine patterns on ceramic samples. In this study, the µPI method for layered material was newly developed to fabricate the micropatterns on both sides of an electrolyte sheet. The optimization of process parameters, such as compounding ratio, debinding temperature, and sintering temperature, was examined to obtain desired wavy patterns on both surfaces of the electrolyte sheet.

The global energy demand has raised concerns about environmental sustainability and economic stability. This has led to significant efforts to identify renewable and green energy sources. Hydrogen production through the water splitting reaction offers a promising pathway, since it yields hydrogen and oxygen as by-products. The photoelectrochemical technique has emerged as one of the effective methods for water splitting, offering vast potential for hydrogen production on a large scale. Among the various semiconductor photoelectrodes, tungsten oxide (WO3) has attracted considerable attention due to its suitable band gap, good chemical stability, and strong absorption in the visible region. This review addresses the fabrication of WO3-based thin films prepared using physical vapor deposition (PVD) techniques, including thermal evaporation, sputtering, pulsed laser deposition (PLD), and electron-beam evaporation. Reported studies highlight that sputtered WO3 films often achieve high photocurrent densities and improved crystallinity, while PLD enables precise control over stoichiometry and nanostructure. Nevertheless, key challenges persist, such as controlling stoichiometry and phase stability, charge-carrier recombination, limited light absorption due to the wide band gap, low conductivity, and structural defects. The review concludes strategies to overcome these limitations, such as conducting thermal and electron-beam evaporation, combining CVD and PVD techniques, and optimizing sputtering conditions.

Recently, while eco-friendly energy storage/conversion technologies have been attracting attention, researches have been reported to improve performance and provide multiple functions by applying three-dimensional nano-/micro-structures to energy devices. In general energy devices, the electrolyte and electrodes located on both sides have been designed to have a flat interface, but in the end, developed structures in consideration of three-dimensional efficiency should be required. Among them, in solid oxide fuel cells (SOFCs), which have advantages such as high efficiency and fuel flexibility, studies on the use of advanced cell structures were conducted to lower the operating temperature. Although micro-SOFC using etching or laser processing has been reported, there are limitations in practical operation due to poor material/structural stability and low pattern resolution. In this paper, we developed a novel ceramic micropatterning process by imprinting a pyramid-shaped polymer mold made by soft lithography on the anode support. Furthermore, we have implemented a three-dimensional SOFC with record-high cell performance through the combination of thin film process and large-area cell manufacturing technology. For microscale patterning of the anode, polymer-ceramic anode films with low elastic modulus was prepared by the tape casting process, and the anode support with pyramidal patterns was fabricated through the subsequent imprinting process. The imprinted pattern was maintained after the sintering process. Then, through RF sputtering and pulsed laser deposition (PLD) process, the nanoscale anode functional layer (nAFL), Y2O3-stabilized ZrO2 (YSZ), Gd0.1Ce0.9O1.95 (CGO) and La0.6Sr0.4CoO3- δ (LSC) layer were deposited to fabricate a full cell. To analyze the electrochemical effect of three-dimensional electrode/electrolyte interface, 3DA-cell with ceramic micropatterning process and Planar-cell with flat interface were compared. Interestingly, 3DA-cell showed higher performance than Planar-cell at all operating temperatures, and resulted in 55 % enhanced maximum power density (PDmax) and 19 %, 52 % decreased polarization, ohmic resistance at 500 °C, respectively. Notably, the CGO-based 3DA-cell using CGO as the main electrolyte material recorded a high PDmax of 0.931 W/cm2 at 500 °C. Therefore, to find the factors that improve the electrochemical performance, the microstructures of two different cells were analyzed by scanning electron microscope (SEM), transmission electron microscopy (TEM) and 3D reconstruction method. From the 3D reconstruction result, the nAFL/YSZ interface area, CGO/LSC interface area, and active TPB length of AFL of 3DA-cell increased by about 33 %. 23 %, and 64 % compared to Planar-cell, whereas pore volume ratio of AFL did not change. Therefore, it was confirmed that the increase of the electrode/electrolyte interface area by ceramic micropatterning had a direct effect on the improvement of cell performance, and the internal structure of AFL was not affected by the imprinting process. Furthermore, to demonstrate the versatility of ceramic micropatterning process, a 5 cm x 5 cm large-area three-dimensional thin film SOFC was fabricated and its performance was evaluated. As a result, we set a new milestone in SOFC technology by reporting a power of ~ 13 W at 500 °C, and confirmed the consistency of our process through a cell reproducibility test. Additionally, the stability of the three-dimensional structure was verified through the operation without notable degradation for 500 hours under the condition of 5 A and 8 A current load. This work exhibits an outstanding breakthrough to accomplish high-performance, high-stable large-area SOFCs, and can accelerate commercialization to the portable and transportation devices.

A solid oxide fuel cell (SOFC) is expected to be applied to the distributed energy systems because of its high thermal efficiency and exhaust gas utilization. The exhaust heat from the SOFC can be transferred to the electric power by a gas turbine, and the high efficiency power generation can be achieved by constructing the SOFC and gas turbine hybrid system. In this study, we analyze the local processes in the electrodes and electrolyte of unit SOFC taking into account the heat conduction, mass diffusion, electrode reactions and the transport of electron and oxygen ion. The temperature and concentration distributions perpendicular to the electrolyte membrane are shown. The effects of the operating conditions on the cell performance are also shown. Furthermore, the entropy generation and exergy loss of each process in the electrodes and electrolyte are analyzed and the reason for generating the exergy loss in the SOFC is clarified. It is noted that two electrode reactions are responsible for the major exergy loss.

Summary: Solid Oxide Fuel Cells (SOFCs) represent a promising technology for efficient and clean energy conversion. This study focuses on the design and development of a novel cathode material for SOFCs, specifically exploring the use of a free-cobalt cathode within a composite structure. Investigating the structure of cobalt-free composites of Ba0.5Sr0.5FeO3-δ (BSF) and Ba0.5Sr0.5Fe0.8B0.2O3-δ (B=Cu, Zn) (BSFB) have been prepared and evaluated as cathodes for IT-SOFCs. The solid-state reaction was employed for generating and modifying the composite structure of the model system. The decomposition reaction and the formation of perovskite structure have been observed using thermal gravimetric analysis and X-ray diffraction. The study encompasses experimental procedures, data processing using GSAS software, and the application of the Rietveld method to achieve precise analysis results. Rietveld analysis outcomes offer intricate details about the crystal structure, encompassing crystal unit parameters, and scale factors. The solid-state reaction led to the reduction in the weight of the composite during the heating process. The decomposition reaction of oxides was generated between 650 to 950 oC. The average of total weight loss during the period treatment was achieved up to 18 % and the perovskite phase formed in the composite structure. A single-phase perovskite from a cubic structure with space group Pm-3m was demonstrated by all composite’s models. The lattice parameter and a unit cell volume were obtained from the model system of BSF, BSFC and BSFZ, respectively. This study explores the potential development of SOFCs technology with the hope of making a positive contribution to advancing clean and sustainable energy solutions in the future

We present a review on fuel cells with emphasis on solid oxide fuel cells (SOFCs). We give an overview of proton exchange membrane, alkaline, phosphoric acid, molten carbonate and direct methanol fuels cells. For SOFCs we discuss electrolytes, anodes, cathodes, interconnects, fabricating processes, materials alternatives and industry. We also give an overview on thermodynamics, electrochemistry and kinetics of fuel cell reactions, mathematical models, fluid dynamics and simulation/computational methods in fuel cells (MM, HF, SE, HF, QM/MM, DFT, MC, MD, FF, Periodic, hybrid, coarse grain). Which are the best SOFCs electrolytes and how they work. We discuss breakthroughs, recent developments and the next generation fuel cells. Keywords: Alkaline, fuel cells, molten carbonate, proton exchange membrane, simulation models, solid oxide.

One of the major advantages of pulsed laser deposition (PLD) for thin- film growth is the use of simply prepared solid targets. Especially for our work with CdTe-related materials in photovoltaics, target preparation by cold pressing from high purity powders works well, partly because the II-VI semiconductors such as CdTe, CdS, and ZnTe do not create serious problems with particulate generation in the PLD plume. Thus we have used mixtures of these binary compounds to produce ternary alloy films with good results. These alloy films are being used to produce band-gap-graded structures in PV cells. In addition, the PLD technique lends itself readily to the preparation of doped films again through appropriate target mixing such as elemental copper mixed into ZnTe or elemental indium mixed into CdS. In addition, doping from the vapor phase by reactive deposition of CdTe in the presence of small pressures of O<SUB>2</SUB> has been successful in reducing the normally very high resistivity of the polycrystalline CdTe Films. Electrical measurements, Raman and photoluminescence, x-ray diffraction, and scanning electron microscopy results from these materials will be presented.