Conventional Thermal Sintering Research Articles

Solution infiltrated lanthanum nickelate–GDC composite cathode via flash-light sintering for intermediate temperature solid oxide fuel cells

Solid oxide fuel cells (SOFCs) require high operating temperatures to minimize the oxygen reduction reaction resistance at cathode and increase the ionic conductivity of oxygen. However, at high operating temperatures, their stability during long-term operation degrades because of material deterioration and the mutual chemical reactions occurring at the interfaces. Herein, an electrode–electrolyte composite is fabricated by solution infiltration of lanthanum nickelate (LNO) electrode material into a GDC electrolyte layer to ensure more reaction sites compared with the conventional powder mixing of the electrode and electrolyte material. Further, the conventional thermal sintering process is replaced with the flash-light sintering process. Thus, the performance of the LNO–GDC cathode cell manufactured by flash-light sintering improves owing to suppression of grain growth of the infiltrated LNO particles. The microstructures of the infiltrated solution and composite layer of the electrolyte material are analyzed using field-emission scanning electron microscopy, and the crystallinity of the LNO nanoparticles is analyzed using high-resolution transmission electron microscopy. A maximum power density of 1.1 W/cm2 is achieved, an improvement of 58 % over the LSCF cell without infiltration at 750 ℃. This study is expected to contribute to the commercialization of SOFCs by replacing conventional thermal sintering.

Vertical-cavity surface-emitting laser (VCSEL)-based ultrafast photonic sintering of solid oxide fuel cells (SOFCs): prospects for time-efficient/two-dimensional scalability to large-sized SOFCs

980 nm VCSEL illumination eliminates the organic additives and densifies the laminated multilayered SOFC NiO–YSZ|NiO–ScCeSZ|ScCeSZ|GDC|GDCscaffold in just 2.42 h compared to >100 h needed for the conventional thermal sintering process.

Comparative studies of structural and dielectric properties of mullite@zirconia composites synthesized by conventional sintering and thermal plasma sintering

Comparative studies of structural and dielectric properties of mullite@zirconia composites synthesized by conventional sintering and thermal plasma sintering

(Invited) A Novel, Ultra-Fast Fabrication of SOFCs By Flash Light Sintering Process

Solid oxide fuel cells (SOFCs) have strong potential for next-generation energy conversion systems because of their high energy conversion efficiency, fuel flexibility and low emission of pollutant. In the last decades, the SOFC technology has rapid progress in terms of performance and durability aspect, expanding its application ranges from stationary system to portable devices. In the fabrication of SOFCs, a simple and mass productive fabrication process such as screen-printing, tape casting and sol-gel method are widely used in the industry because it is easy, scalable and economical process. However, a high temperature post heat-treatment process is required to ensure material properties of the ceramic electrolyte and electrode in these processes. In particular, to achieve a highly dense electrolyte layer, a high sintering temperature above 1300oC is usually employed in the fabrication process, which causes considerable amount of time and significant manufacturing costs. Therefore, reducing the sintering temperature and long process time is one of the major challenges to reduce the fabrication cost and facilitate the commercialization of SOFCs. To overcome this problem, many efforts have been made to demonstrate alternative sintering process to reduce the sintering temperature and process time. For example, several researchers proposed spark plasma sintering process as an alternative sintering process because of the high heating rate within a short time based on Joule heating mechanism [1, 2]. However this process has a limitation of complex vacuum system configuration and high equipment cost for commercialization. In addition, excimer laser ablation annealing and microwave sintering process have been also suggested but there are still limitations such as extremely narrow spot size and complexity of microwave interactions with materials respectively [3, 4]. On the other hand, the flash light sintering process presented here uses a white flash light generated by a xenon arc lamp discharge as a heat treatment sources and has many advantages of an extremely short process time, scalability and simple process condition as standard ambient and temperature. Most of all, because this process conducted within a few seconds, it can significantly improve the productivity and cost-effectiveness of the SOFCs. Our previous works successfully demonstrated that the solution-based YSZ thin films was annealed by flash light sintering and it showed comparable material properties to the conventional thermal sintering process [5]. Nevertheless, due to the low light absorption property and difficulty to sinter the ceramic particles, studies on the flash light sintering process for the powder-based films are still limited. In this work, we demonstrate for the first time rapid fabrication of SOFCs using a novel flash light sintering process. The ceramic electrolyte and electrode was fabricated by using mass productive screen-printing method and flash light sintering process was employed as an alternative sintering process of conventional thermal sintering method. In the sintering process, the effect of various pulse conditions on the sinterbility of the ceramic components were investigated, and the material properties such as microstructure, crystallinity and electrochemical property were analyzed. The optimized ceramic components were employed to fabricate SOFC unit cell and their cell performance and impedance behavior was evaluated to demonstrate the flash light sintering process. Reference [1] Deepash Shekhar Saini et al. “Improved conductivity of spark plasma sintered Ho-Substituted Ba-ZrO3 electrolyte ceramics for IT-SOFCs.” ACS Applied Energy Materials. 1, 7, 3469-3478 (2018)[2] Tatiana L. Simonenko et al. “Spark plasma sintering of nanopowders in the CeO2-Y2O3 system as a promising approach to the creation of nanocrystalline intermediate-temperature solid electrolytes.” Ceramics International, 44, 16, 19879-19884 (2018)[3] Hao, H., Xu, L., Huang, Y., Zhang, X. & Xie, Z. “Kinetics mechanism of microwave sintering in ceramic materials.” Science in China Series E: Technological Sciences 52, 2727–2731 (2009).[4] Bayati, R. et al. “Modifcation of properties of yttria stabilized zirconia epitaxial thin flms by excimer laser annealing.” ACS applied materials & interfaces 6, 22316–22325 (2014).[5] Park, J.S. et al. Rapid, cool sintering of wet processed yttria-stabilized zirconia ceramic electrolyte thin films. Scientific reports 7, 12458 (2017)

Flash Light Sintered SOFC Cathode Functional Layer through Electrostatic Spray Deposition

Solid oxide fuel cells(SOFCs), which are attracting attention as an eco-friendly power generation system, are being actively studied due to their fuel flexibility and high efficiency. Since the charge carriers are oxygen ions and have to pass through the solid oxide electrolyte, they require a higher operating temperature (~900 oC) than other fuel cells. To overcome the disadvantages of high-temperature operation, research is being conducted to lower the operating temperature of the SOFCs. In particular, in order to minimize performance degradation even at low operating temperatures, research is being conducted to fabricate cell components as thin films or to apply electrodes with high catalytic activity and large reaction areas.Among the methods of manufacturing thin films, the deposition method using chemical solution deposition(CSD) has the advantage of being cost effective and easily controllable compared to the vacuum deposition method. Electrostatic spray deposition(ESD), one of the CSD deposition methods, is simple to set-up and a variety of compounds can easily be made by controlling the proportions of the precursors. However, a characteristic of the CSD method is that a post heat treatment process is required to obtain desired properties, which consumes a lot of time and cost during the entire process. To solve this problem, processes such as rapid thermal annealing, microwave, and excimer laser ablation are being studied, but these processes have limitations in that they damage the substrate, have a long cooling time, and have a small sintering area. [1, 2] On the other hand, the flash light sintering method using a xenon lamp can perform a post-heat treatment process quickly at room temperature and atmospheric pressure using intense pulsed light, and has the advantage of minimizing damage to the substrate and being applicable to a large area. [3, 4]In this study, the cathode functional layer, which is closely related to the performance of SOFC, was fabricated using the ESD method, and the flash light sintering method was applied for the post-heat treatment process. By applying the flash light sintering method, the heat treatment process, which used to take tens of hours, was shortened to just a few seconds. The sintering behavior of the film produced by flash light sintering was confirmed by comparing the microstructure and crystallinity. In addition, it was confirmed that the film manufactured by flash light sintering worked successfully by comparing the performance with the cell manufactured by the conventional thermal sintering method. Reference [1] R. Bayati et al., "Modification of Properties of Yttria Stabilized Zirconia Epitaxial Thin Films by Excimer Laser Annealing," (in English), Acs Applied Materials & Interfaces, vol. 6, no. 24, pp. 22316-22325, Dec 24 2014.[2] H. S. Hao, L. H. Xu, Y. Huang, X. M. Zhang, and Z. P. Xie, "Kinetics mechanism of microwave sintering in ceramic materials," (in English), Science in China Series E-Technological Sciences, vol. 52, no. 9, pp. 2727-2731, Sep 2009.[3] J. S. Park, D. J. Kim, W. H. Chung, Y. Lim, H. S. Kim, and Y. B. Kim, "Rapid, cool sintering of wet processed yttria-stabilized zirconia ceramic electrolyte thin films," (in English), Scientific Reports, vol. 7, Sep 29 2017.[4] J. S. Park, H. Lee, S. Heo, and Y. B. Kim, "Heater-assisted intense pulsed light irradiation for lanthanum strontium cobaltite thin film electrode fabrication," (in English), Thin Solid Films, vol. 697, Mar 1 2020.

Fabrication of Nano Samarium Doped Ceria(SDC) Infiltrated La6Sr4Co2Fe8O3-δ(LSCF) Composite Cathode for High Performance It-SOFCs

The solid oxide fuel cells(SOFCs) use oxygen ions generated by an oxygen reduction reaction(ORR) supplied to the cathode as charge carrier. Oxygen ions transferring across the solid oxide electrolyte via a hoping mechanism require a high operating temperature to overcome the low ionic conductivity. High ionic conductivity and performance can be obtained at high operating temperature, but the stability is reduced during operation condition due to deterioration of component materials and mutual chemical reactions at the interface. For this reason, researches have proceeded to lower operating temperature of to the intermediate temperature regime(650~750℃) and to develop the electrode layers having high performance at the lower operating temperature. However, since the oxygen reduction reaction resistance is increased, the performance of the SOFCs is reduced at the lower operating temperature. Therefore, many research institutes of fuel cells have added the composite cathode functional layer(CFL) to improve the fuel cell performance between electrolyte and electrode layers using various methods, composite powder, and infiltration. [1, 2] In this study, the solid oxide fuel unit cells are fabricated having the electrolyte/electrode composite layer which was applied to the LSCF electrode infiltrated with nanoparticle SDC for obtaining the many reaction site compared with conventional powder composite materials. When the LSCF-SDC composite cathode functional layer is manufactured, it is applied that the novel flash light sintering method replace the conventional thermal sintering method. Since it can finish the manufacturing process in seconds, the LSCF-SDC cathode layer has the LSCF cathode with nanoparticle SDC suppressed grain growth of the particles which can contribute to improving the performance of the fuel cells.[3] The microstructure of the infiltrated solution and the composite layer of the electrolyte material is analyzed using scanning electron microscopy (FE-SEM) and transmission electron microscopes energy dispersive spectroscopy (TEM-EDS). The crystallinity of nanoparticle SDC is analyzed using FR-TEM and X-ray diffraction. And, the electrochemical analysis of LSCF-SDC cathode cell is carried out at 650~750°C. The performance improvement of the solid oxide fuel cell at intermediate operating temperature is maximized through the fabrication of the cathode functional layer using the solution infiltration method and the alternative flash light sintering process. Reference [1] J. Hong, A. Bhardwaj, Y. Namgung, H. Bae, S.-J. Song, Evaluation of the effects of nanocatalyst infiltration on the SOFC performance and electrode reaction kinetics using the transmission line model, Journal of Materials Chemistry A, 8 (2020) 23473-23487.[2] J. Shin, S. Yang, H.-I. Ji, S. Park, H. Kim, J.-W. Son, J.-H. Lee, B.-K. Kim, J. Hong, K.J. Yoon, Low-temperature processing technique of Ruddlesden-Popper cathode for high-performance solid oxide fuel cells, Journal of Alloys and Compounds, 868 (2021) 159092.[3] Y. Lim, J. Park, H. Lee, M. Ku, Y.-B. Kim, Rapid fabrication of lanthanum strontium cobalt ferrite (LSCF) with suppression of LSCF/YSZ chemical side reaction via flash light sintering for SOFCs, Nano Energy, 90 (2021) 106524.

Does plasma jet sintering follow an Arrhenius‐type expression?

AbstractAtmospheric pressure, ambient temperature plasma jets have become a promising candidate for material processing in parallel with developments in additive manufacturing. Recent work has shown that plasma jets can be used to sinter printed nanoparticles at temperatures much lower than typically required for conventional thermal sintering. Here, we conduct a mechanistic study on plasma jet sintering that correlates specific energy input with the electrical conductivity of printed silver films after sintering. Increasing the specific energy input accelerated the sintering process following an Arrhenius‐like exponential trend across a large range of conditions, including both helium and argon plasma jets. Although an exponential relationship is also found with the plasma heated substrate temperature, independent studies indicate that heating is not the primary mechanism. These results suggest there is a general behavior that couples the plasma jet with the surface.

ESB 소결 조제를 이용한 고체산화물 연료전지용 YSZ 전해질의 초고속 광소결 공정에 관한 연구

A high temperature sintering process for solid electrolyte is the main cause of the increase in manufacturing costs of SOFCs. In this study, we developed a novel flash light sintering technique as an alternative sintering process of the conventional thermal sintering process. The YSZ electrolyte films were fabricated by conventional screen-printing method and the flash light sintering process and ESB sintering aid were applied to improve the flash light sinterability of the YSZ electrolyte. In the flash light sintering process, the effect of various pulse conditions such as energy density, and pulse interval were investigated and the microstructure, crystallinity, and sintering behavior of the sintered films were analyzed to demonstrate the effectiveness of the flash light sintering process. The flash light sintered YSZ electrolyte layer was used to fabricate the anode-supported SOFCs and its functionality is successfully demonstrated with the high open circuit voltage. The significance of this study includes minimization of the process time from tens of hours to just a few seconds, thus facilitating the commercialization of SOFCs.

Effect of laser power on conductivity and morphology of silver nanoparticle thin films prepared by a laser assisted electrospray deposition method

Silver nanoparticle-based electrodes were studied extensively in recent years as an electrode material for wearable and flexible electronics due to their stability and conductivity. A wet chemical deposition technique is considered as a low-cost scalable technique. The current wet chemical-based nanoparticle deposition techniques include electrospray deposition, drop casting, spin coating, and the inkjet printing process. These techniques generally require a separate postdeposition annealing step. This can be a problem for substrates with a low melting point. In addition, some of the above-mentioned methods require physical contact, which increases the probability of cross-contamination. In this research, we present a technique that combines electrospray and laser radiation to deposit and sinter nanoparticles simultaneously on a rigid or flexible substrate. In this process, the microdroplets of aqueous silver nanoparticle suspension ejected in what is known as the microdripping mode from a metallic capillary nozzle, which can be controlled by an electric potential. A conical hollow laser beam is used to vaporize the liquid and sinter the nanoparticles at desired locations on a substrate. This is a promising technique compared to the traditional methods to fabricate conductive micropatterns due to its simplified one step deposition, suppressed cross-contamination, and applicability to various surfaces. Thin-film micropatterns of silver nanoparticles were fabricated using a Nd:YAG laser with powers from 5 to 13 W. The correlation between the grain size distribution, composition, and electrical resistivity was studied using a scanning electron microscope, energy-dispersive x ray, and four-point probe analysis. The results are comparable to the conventional thermal sintering method.

Flash light sintered SDC cathodic interlayer for enhanced oxygen reduction reaction in LT-SOFCs

To commercialize solid oxide fuel cells, many methods for reducing the production time of manufacturing a fuel cell membrane-electrode-assembly (MEA) using a non-vacuum process have been studied and still the post-heat treatment process is an issue. This paper discusses an alternative sintering method to replace the conventional thermal sintering step for ceramic thin film fabrication, which is time consuming and costly. We fabricated samarium-doped ceria (SDC) thin films, which has high ionic conductivity and high surface exchange coefficient for oxygen reactions at the cathode side. The films were deposited by chemical solution deposition (CSD) method utilizing electrostatic spray deposition (ESD) technique. Thermal decomposition and crystallization steps are required as a post-heat treatment process to obtain desired material properties. For this purpose, the flash light sintering method is adopted and compared with the conventional thermal sintering process using halogen furnace. With this flash light sintering method, the conventional post-heat treatment process time can be significantly reduced from tens of hours to a few seconds. Scanning electron microscopy, X-ray diffraction, and transmission electron microscopy analyses were carried out for material characterizations. Additionally, electrochemical impedance analysis and current-voltage behavior measurements were conducted. By successful fabrication of SDC cathodic functional layer utilizing flash light irradiation process, the 2-folds of fuel cell performance enhancement was obtained in terms of the peak power density at the measurement temperature of 450 °C.

Cold sintering ZnO based varistor ceramics with controlled grain growth to realize superior breakdown electric field

Controlling the grain growth and grain boundary morphology is of great importance in the manipulation of electrical properties of electro-ceramics. However, it has been a challenge to achieve dense varistor ceramics with grain sizes in submicrons and nanometers using conventional thermal sintering at high temperatures. Here we present a strategy to fabricate dense ZnO based ceramics with controlled grain growth and thin grain boundaries using cold sintering process (CSP). With CSP, the sintering temperature of ZnO based ceramics dramatically drops from 1100 °C to 300 °C. The Bi2O3, Mn2O3, and CoO dopants suppress the grain growth of ZnO under CSP conditions, and Bi-rich intergranular films (2−5 nm) can be observed along grain boundaries. The cold sintered ZnO-Bi2O3-Mn2O3-CoO ceramic shows a non-linear coefficient of 33.5, and a superior breakdown electric field of 3550 V/mm. This work thus demonstrates that CSP is a promising technique for designing new submicron-/nano-ceramics with superior performances.

Size effect on the thermal expansion of ZrO2/ZrW2O8 composites fabricated by the conventional sintering process

The size effect on the thermal expansion of ZrO2/ZrW2O8 fabricated by the conventional thermal sintering process is investigated systematically. The small-sized sample with dense microstructure and few ZrW2O8 decomposition exhibits near-zero thermal expansion. While the microstructure and thermal expansion property of the large-sized sample deteriorates due to the serious decomposition of ZrW2O8. The finite element analysis is used to investigate the thermal transfer during the quenching, demonstrating that the smaller specific surface area (SSA) of the large-sized sample is the direct reason of the size effect, and the core causes are the instability of ZrW2O8 and the low thermal conductivity of the ZrO2/ZrW2O8. A thermal conductive pathway is further designed for the large-sized sample to verify and attenuate the size effect by increasing the SSA. The technique of ultra-low sintering temperature is urgently recommended to effectively solve the obstruction caused by the size effect.

Fabrication and characterization of Ag flake hybrid circuits with IPL-sintering

The study of photonic sintering has gained interest based on the advantages of fast processing at room temperature. However, printed electronics made from photonic sintering with an intensive pulsed light (IPL) energy source exhibit more mechanical instability than those made from conventional thermal sintering processes. To solve the mechanical instability problems, we fabricated Ag flake hybrid pastes with a variety of concentrations of Ag flake (0, 25, 50, 75, and 100 wt.%). All of the screen-printed hybrid Ag circuits were fabricated on polyimide substrates and were sintered at 3.5 MW. Surface porosity was analyzed using the Brunauer-Emmett-Teller method. An IPC (Packaging Electronic Circuits) sliding test was performed to analyze the flexibility of the screen-printed Ag flake hybrid circuits. The adhesion strength of the hybrid circuits was evaluated with a roll-type 90° peel test. The hybrid Ag printed circuit showed improvements in both the flexibility and adhesion strength with the addition of Ag flake.

Current-ramp assisted sintering of 3YSZ: Electrochemical and microstructural comparison to flash and thermal sintering

Flash sintering features an unoptimized and uncontrolled rise in current density and sample conductivity. By using a controlled current-ramp technique with a predetermined ramp function, microstructure and electrochemical properties can be improved. This current-ramp method is investigated through use of test functions that follow square-root, linear, and parabolic time dependence with comparison to conventional flash sintering and thermal sintering. Steeper ramp functions during the sintering result in higher activation energy, suggesting a change in the vacancy concentration for both the bulk and grain boundary regions. Estimation of the grain boundary domain width suggests a grain size dependence of the unique space charge contribution to conduction independent of sintering method. Contrary to conventional wisdom, flash sintering can actually result in enhanced grain growth compared to controlled current-ramps and conventional sintering, implying that uncontrolled rise in current to a set cutoff may not be the optimal method for densification.

Rapid Fabrication of Chemical Solution-Deposited Lanthanum Nickelate Thin Films via Intense Pulsed-Light Process

In this paper, we demonstrate the practicality and feasibility of the flash light-sintering method to fabricate the ceramic material perovskite structure for lanthanum nickel oxide (LaNiO3; LNO) thin films using flash light irradiation equipment. LNO thin films are deposited on an Si wafer and Al2O3 substrate via the chemical solution deposition (CSD) method and sintered by a thermal and flash light-irradiation process with a bottom heater. The properties of flash light-sintered LNO thin films are compared with those of thermally sintered films. The surface morphology, crystal development, and electric conductivity of the LNO thin films are measured by field-emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD), and a four-point probe, respectively. Flash light sintering was accomplished in milliseconds. Through the comparison of thermal sintering and flash light-sintering results, it was confirmed that perovskite LNO thin films deposited by the CSD method can be fabricated by flash light sintering. We show that the flash light sintering method can solve several inherent issues of the conventional thermal sintering method.

Combined Chemical and Thermal Sintering for High Conductivity Inkjet-printed Silver Nanoink on Flexible Substrates

Electrical conductivity is a key factor in measuring performance of printed electronics,<br /> but the conductivity of inkjet-printed silver nanoinks greatly depends on post-fabrication<br /> sintering. In this work, two different conductive silver nanoinks, in which the silver nanoparticles were stabilized by two different capping agents – Poly(acrylic acid) (PAA) and Poly(methacrylic acid) (PMA) – were synthesized. The inks were inkjet-printed on flexible PET substrates, coated with an additional polycation layer, which facilitated<br /> chemical sintering. The printed features were then exposed to moderately elevated<br /> temperatures to evaluate the effect of combined chemical and thermal sintering. Both<br /> inks produced conductive features at room temperature, and the conductivity increased<br /> with both temperature and duration of sintering. At temperatures above 100 °C, the choice of capping agent had no pronounced effect on conductivity, which approached very high values of 50 % of bulk silver in all cases. The lowest resistivity (2.24 μΩ cm) was obtained after sintering at 120 °C for 180 min. By combining chemical and conventional thermal sintering, we have produced remarkably conductive silver electrodes on flexible substrates, while using low-cost and simple processes.

Selective Laser Sintering of Laser Printed Ag Nanoparticle Micropatterns at High Repetition Rates.

The increasing development of flexible and printed electronics has fueled substantial advancements in selective laser sintering, which has been attracting interest over the past decade. Laser sintering of metal nanoparticle dispersions in particular (from low viscous inks to high viscous pastes) offers significant advantages with respect to more conventional thermal sintering or curing techniques. Apart from the obvious lateral selectivity, the use of short-pulsed and high repetition rate lasers minimizes the heat affected zone and offers unparalleled control over a digital process, enabling the processing of stacked and pre-structured layers on very sensitive polymeric substrates. In this work, the authors have conducted a systematic investigation of the laser sintering of micro-patterns comprising Ag nanoparticle high viscous inks: The effect of laser pulse width within the range of 20–200 nanoseconds (ns), a regime which many commercially available, high repetition rate lasers operate in, has been thoroughly investigated experimentally in order to define the optimal processing parameters for the fabrication of highly conductive Ag patterns on polymeric substrates. The in-depth temperature profiles resulting from the effect of laser pulses of varying pulse widths have been calculated using a numerical model relying on the finite element method, which has been fed with physical parameters extracted from optical and structural characterization. Electrical characterization of the resulting sintered micro-patterns has been benchmarked against the calculated temperature profiles, so that the resistivity can be associated with the maximal temperature value. This quantitative correlation offers the possibility to predict the optimal process window in future laser sintering experiments. The reported computational and experimental findings will foster the wider adoption of laser micro-sintering technology for laboratory and industrial use.

Fast Fabrication of SOFCs with Screen-Printed YSZ Electrolyte Films By Flash Light Sintering

Solid oxide fuel cells (SOFCs) are attractive energy conversion system because of their high energy conversion efficiency, fuel flexibility and no emission of pollutant. SOFCs are composed of a dense electrolyte and two porous electrodes of anode and cathode. In the fabrication of SOFCs, many fabrication techniques such as screen-printing, tape casting, sol-gel, sputtering, chemical vapor deposition (CVD) and atomic layer deposition (ALD) are used to fabricate the solid electrolyte and the electrodes. Among various fabrication techniques, screen-printing is most widely used method in the industry because it is easy, scalable and economical process. Meanwhile, for the fabrication of solid electrolyte in this technique, high temperature sintering process is essential because the electrolyte should be fully densified to prevent any penetration of electrons and fuels. However, this high process temperature takes a considerable amount of time and thus causes significant manufacturing costs. Therefore, reducing the sintering temperature and long process time is one of the major challenges to reduce the fabrication cost and facilitate the commercialization of SOFCs. In recent years, to address these issues, many researchers demonstrated alternative sintering processes to reduce the sintering temperature and process time. For example, several researchers proposed rapid thermal annealing (RTA) process as an alternative sintering process because it can raise temperature to the target temperature within short time [1,2]. However, this process still requires relatively long maintaining and cooling processes. In addition, the excimer laser ablation annealing and the microwave sintering process have been also suggested but there are still limitations such as extremely narrow spot size and complexity of microwave interactions with materials respectively [3,4]. On the other hand, the flash light sintering process presented here uses white light flash irradiation with a broad visible wavelength range as a heat treatment source and this process has many advantages such as simplicity, scalability, and cost-effectiveness. Above all, because this process conducted within a few seconds at room temperature under ambient conditions, it can effectively reduce the manufacturing time and cost. Our previous works successfully demonstrated that the YSZ thin films deposited by solution-based process was annealed by flash light sintering and it showed comparable material properties to the conventional thermal sintering process [5]. In this work, the YSZ electrolyte films were fabricated by conventional screen-printing method and flash light sintering process was employed as an alternative sintering process of conventional thermal sintering method. In the sintering process, the effect of various pulse conditions and additional substrate heating were investigated. Microstructure, crystallinity and sintering behaviors of sintered films were analyzed to demonstrate the effectiveness of flash light sintering process. Reference [1] Wang, S. J. & Ong, C. K. Rapid thermal annealing efect on crystalline yttria-stabilized zirconia gate dielectrics. Semiconductor Science and Technology 18, 154 (2003). [2] Beltrán, N. H., Balocchi, C., Errazu, X., Avila, R. E. & Piderit, G. Rapid thermal annealing of zirconia flms deposited by spray pyrolysis. Journal of Electronic Materials 27, L9–L11 (1998). [3] Hao, H., Xu, L., Huang, Y., Zhang, X. & Xie, Z. Kinetics mechanism of microwave sintering in ceramic materials. Science in China Series E: Technological Sciences 52, 2727–2731 (2009). [4] Bayati, R. et al. Modifcation of properties of yttria stabilized zirconia epitaxial thin flms by excimer laser annealing. ACS applied materials & interfaces 6, 22316–22325 (2014). [5] Park, J.S. et al. Rapid, cool sintering of wet processed yttria-stabilized zirconia ceramic electrolyte thin films. Scientific reports 7, 12458 (2017)

Novel proton-conducting nanocomposites for hydrogen separation membranes

Design of oxide and nanocomposite materials with high mixed protonic-electronic conductivity such as lanthanide niobates and tungstates is encouraging approach in developing hydrogen separation membranes. This work aims at elucidating the relation of structure, oxygen and protonic mobility of such materials. La0.99Ca0.01NbO4, LaNb3O9 and Nd5.5WO11.25−δ were synthesized by Pechini and citrate route. Nanocomposites with LaNb3O9 and Ni + Cu were prepared by ultrasonic dispersion or mechanical treatment in a high energy mill and wet impregnation, then sintered using conventional thermal sintering and hot pressing. All obtained materials were characterized using XRD, SEM, TEM with EDX analysis, IR and Raman spectroscopy. The oxygen and proton mobility were studied by isotope exchange, unit cell volume and weight relaxation techniques. The proton conductivity was studied by Van der Pauw technique. The main phases were scheelite for La0.99Ca0.01NbO4, perovskite for LaNb3O9 and fluorite for Nd5.5WO11.25−δ, extended defects were observed agreeing with IR and Raman spectroscopy data. The oxygen mobility studies revealed two types of bulk oxygen related to two phases in samples. D2O exchange studies demonstrated very fast protonic transport in samples. H2O desorption experiments revealed the working temperature range being 300–450 °C. The protonic conductivity values (~10−4 Ω−1 cm−1 at 400 °C) agree with the literature data and are sufficiently high for the practical application. Proton tracer and chemical diffusion coefficients values are ~10−11 and ~10−3 cm2/s at working temperatures, respectively. Successful test of proton conducting membrane with Nd5.5WO11.25−δ based functional layer showing promising performance has been carried out.

Highly-conductive proton-conducting electrolyte membranes with a low sintering temperature for solid oxide fuel cells

The microwave sintering strategy was for the first time adopted to prepare proton-conducting electrolyte membranes for solid oxide fuel cells. The preparation of a dense proton-conducting BaCe0.7Zr0.1Y0.2O3-δ (BCZY) electrolyte membrane can be achieved at 1200 °C with the microwave sintering method. In sharp contrast, a BCZY sample prepared at 1200 °C using the conventional thermal sintering method was found to be porous. In comparison with a dense BCZY sample prepared at 1400 °C using the conventional sintering method, the microwave-sintered BCZY electrolyte showed an improved proton conductivity, which is beneficial for fuel cell applications. Experimental results showed that the microwave sintering method enabled a homogenous elemental distribution and a suppression of barium evaporation, leading to the conductivity improvement in both bulk and grain boundaries. With the microwave sintered BCZY film as the electrolyte, a proton-conducting solid oxide fuel cell delivered a maximum power density of 838 mW cm−2 at 700 °C with an electrolyte film conductivity as high as 1.4 × 10−2 S cm−1. This study suggests that the microwave sintering method is a promising strategy to prepare electrolyte membranes at a relatively low temperature with high conductivity, which could advance the development of proton-conducting solid oxide fuel cells.