Protonic Ceramic Research Articles

Regulation of Cathode Mass and Charge Transfer by Structural 3D Engineering for Protonic Ceramic Fuel Cell at 400 °C (Adv. Funct. Mater. 33/2021)

3D Engineering In article number 2102907, Wei Wu, Meng Zhou, Dong Ding, and co-workers develop a 3D engineered cathode to enhance oxygen reduction reaction kinetics on a proton-conducting fuel cell at <600 °C. The results demonstrate remarkable cell performance at 400–600 °C by effectively regulating the mass and charge transfer through the electrode and across the interface of electrolyte and electrode.

Modeling and Techno-Economic Analysis of High Temperature Electrolysis Systems Using Protonic Ceramics

High temperature water splitting (HTWS) via electrochemical processes are of growing interest due to their potential for achieving high thermodynamic efficiency. In particular, protonic ceramic electrolysis cells (PCECs) operating between 500°-600°C have the attractive feature that, in theory, pure dry hydrogen is produced at the hydrogen electrode (see Figure 1) and, unlike more conventional solid oxide electrochemical cells (SOECs) operating at 800°C, no further gas separation is needed. These features allow much simpler and elegant hydrogen production system concepts that have the potential to be significantly less costly and more efficient. For example, the dry H2 gas production at the fuel electrode allows for a much simpler balance-of-plant. The lower operating temperature also has numerous benefits, including lower plant heat losses, the ability to find more options for integrating various process heat sources by virtue of the lower grade heat requirements, and reduced capital cost due to a reduction in both gas process heat exchanger temperature and surface area requirements. A simple thermodynamic evaluation indicates that balance-of-plant steam generation specific energy (kJ/kg) requirements are some 17% lower when operating at 500°C versus 800°C.The present work focuses on scale-up of advancing PCEC material sets developed by collaborating faculty at the Colorado School of Mines and an industrial partner, and their design/integration into MW-scale hydrogen production systems. Realizing high efficiency HTWS systems based on novel protonic ceramics requires understanding of numerous system-level considerations. One of our efforts is largely concerned with developing viable system designs that enable >75% system efficiency at centralized hydrogen production costs of < $2/kg (without compression, dispensing, and storage). This requires evaluation of plant operating conditions, especially in the PCEC stack periphery, where operating temperature, pressure, reactant utilization, sweep gas (if any) on the fuel electrode, thermal management, gas compression, and balance-of-plant integration all play critical roles in establishing cost effective, high performance HTWS systems. In this presentation, validated PCEC models using the latest large platform experimental cell data are used to explore optimal stack design parameter selection, such as cell voltage, reactant utilization, and reactant supply composition. System design implications from parameter sensitivity studies is summarized, and a comparative techno-economic analysis of PCEC-based hydrogen production systems with SOEC and PEMEC technologies is given. Figure 1

Improvement in Power Density of Protonic Ceramic Fuel Cells with Yb Doped BaZrO3 Electrolyte

Protonic ceramic fuel cells (PCFCs) have attracted much attention due to potential to achieve ultra-high energy-conversion efficiency. Besides high efficiency, high power density even at lower temperatures is needed to widespread application. We selected Yb doped BaZrO3 as the electrolyte material of our PCFCs and then developed anode-supported PCFCs. The resulting power density of the PCFCs at 600°C reached 0.4 W cm－2.

First-Principles Investigation on the BaM 2NiO5 Second Phase in Ba(Zr,M)O3 Solid Electrolyte in Proton-Conducting Solid Oxide Fuel Cell

BaZrO3, in which Zr sites are substituted with rare earth elements M, has been investigated for use as a solid electrolyte in Protonic Ceramic Fuel Cells (PCFC). However, co-sintered electrodes-derived Ni solution causes second phase formation of BaM 2NiO5 [1] and decrease of rare earth element solution level in BaZrO3. This problem greatly limits the operating temperature of the PCFCs and the selection of additive elements. In addition, the formation mechanism of the BaM 2NiO5 is still unclear. Even if the formation of BaM 2NiO5 is not confirmed in short-time synthesis experiments, it may precipitate during long-term operation, leading to degradation of the PCFCs. Thus, in this study, we investigated the formation tendency of BaM 2NiO5 and the precipitation mechanism in Ba(Zr,M)O3 by using first-principles calculations. All first-principles calculations were performed using the VASP code [2] with the consideration of spin polarization. Interactions between ions and electrons were described by the Projected Augmented Wave (PAW) method [3]. Perdew–Burke–Ernzerhof revised for solids (PBEsol) was utilized to approximate exchanges and correlate interactions of electrons [4,5]. 4f electron of M elements (M = Lu, Yb, Tm and Gd) was assumed to be treated as a frozen core state. The kinetic cut-off energy for the plane wave was 500 eV. The k-point mesh for integration in the Brillouin zone was carefully selected as a Γ-point centered dense k-mesh. These calculation conditions were confirmed to be sufficient to acquire well-converged total energy, below 0.1 meV/atom. Atomic positions and cell parameters of each structure were optimized until the forces on each atom and cell converged below 1×10-4eV/Å. Figure 1 (a) shows the schematic illustration of BaM 2NiO5 primitive cell. Formation energies of BaM 2NiO5 were evaluated by energy differences between BaM 2NiO5 and sum of the energy of each single oxide (BaO, M 2O3 and NiO). Figure 1 (b) shows the evaluated formation energies of BaM 2NiO5 (M = Sc, In, Lu, Yb, Tm, Y and Gd). BaSc2NiO5 and BaIn2NiO5 were found to be energetically unstable due to their positive formation energies. On the other hand, formation energies of BaLu2NiO5, BaYb2NiO5, BaTm2NiO5, BaY2NiO5 and BaGd2NiO5 show negative values. However, experimentally, the precipitation of BaLu2NiO5 and BaYb2NiO5 has not been confirmed [1]. This discrepancy can be attributed to the fact that the equilibrium condition including Zr was not considered in first-principles calculation. Therefore, considering the equilibrium condition of precipitation of Ba2 MNiO5 in Ba(Zr, M, Ni)O3, the experimentally confirmed threshold of precipitation is located around the formation energy of -0.4 eV/f.u. in Fig. 1(b). For the very early stage of the actual precipitation mechanism of Ba2MNiO5, it is thought that the binding energy between cations in Ba(Zr, M, Ni)O3 is involved. This point is still under investigation and will be discussed in detail on the day of the presentation.

Joining the BaZr0.1Ce0.7Y0.1Yb0.1O3-δ Electrolyte to AISI 441 Interconnect for Protonic Ceramic Fuel Cell Applications: Interfacial Microstructure and Long-Term Stability

Joining the BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δ Electrolyte to AISI 441 Interconnect for Protonic Ceramic Fuel Cell Applications: Interfacial Microstructure and Long-Term Stability

Building Ruddlesden–Popper and Single Perovskite Nanocomposites: A New Strategy to Develop High‐Performance Cathode for Protonic Ceramic Fuel Cells

Here a new strategy is unveiled to develop superior cathodes for protonic ceramic fuel cells (PCFCs) by the formation of Ruddlesden-Popper (RP)-single perovskite (SP) nanocomposites. Materials with the nominal compositions of LaSrx Co1.5 Fe1.5 O10- δ (LSCFx, x=2.0, 2.5, 2.6, 2.7, 2.8, and 3.0) are designed specifically. RP-SP nanocomposites (x=2.5, 2.6, 2.7, and 2.8), SP oxide (x=2.0), and RP oxide (x=3.0) are obtained through a facile one-pot synthesis. A synergy is created between RP and SP in the nanocomposites, resulting in more favorable oxygen reduction activity compared to pure RP and SP oxides. More importantly, such synergy effectively enhances the proton conductivity of nanocomposites, consequently significantly improving the cathodic performance of PCFCs. Specifically, the area-specific resistance of LSCF2.7 is only 40% of LSCF2.0 on BaZr0.1 Ce0.7 Y0.2 O3- δ (BZCY172) electrolyte at 600°C. Additionally, such synergy brings about a reduced thermal expansion coefficient of the nanocomposite, making it better compatible with BZCY172 electrolyte. Therefore, an anode-supported PCFC with LSCF2.7 cathode and BZCY172 electrolyte brings an attractive peak power output of 391 mW cm-2 and excellent durability at 600°C.

Low‐Temperature Protonic Ceramic Fuel Cells through Interfacial Engineering of Nanocrystalline BaCe0.7Zr0.1Y0.1Yb0.1O3−δ Electrolytes

Nanocrystalline BaCe0.7Zr0.1Y0.1Yb0.1O3−δ (BCZYYb) is designed by a novel strategy with improved proton transport properties at low temperatures (&lt;300 °C). In situ Raman spectroscopy and electrical conductivity relaxation (ECR) are used to quantitatively evaluate the surface exchange coefficients during the hydrogen isotope exchange process. Similar surface exchange coefficients are measured via in situ Raman spectroscopy and ECR measurements, representing new tools to better understand proton transport behaviors at the materials’ interface. The surface exchange coefficient in nanocrystalline BCZYYb is nearly four times higher than that in conventional dense BCZYYb at 300 °C, indicating higher surface mobility of protonic species in the designed BCZYYb membrane. The improved performance originates from the combined interfacial and bulk effects for proton transport at low temperatures. In addition, low‐temperature protonic ceramic fuel cells (PCFCs) are built based on a nanocrystalline BCZYYb electrolyte with improved single‐cell performance at 300 °C, which indicates enhanced proton transport properties in contemporary energy conversion and storage materials can be achieved through interfacial engineering.

Improvement in Power Density of Protonic Ceramic Fuel Cells with Yb Doped BaZrO3 Electrolyte

This paper reports our development of protonic ceramic fuel cells (PCFCs) with BaZr0.8Yb0.2O3−δ (BZYb) electrolyte. Although PCFCs can theoretically achieve ultra-high energy-conversion efficiency for power generation, higher power density even at lower temperatures below 600°C is required to widespread application. Here, a zirconate-based oxide of BZYb was selected as electrolyte material of PCFCs because of its high chemical stability against CO2. Also, cost-effective conventional wet processes were used to fabricate the PCFCs. High-temperature co-sintering successfully produced a dense and thin BZYb electrolyte. The PCFC showed a stable operation for 400 h without significant degradation. Investigation into changing parameters of large-size PCFCs (50 × 50 mm) such as anode porosity, interlayer function, electrolyte thickness, and cathode material improved the power density of the PCFCs with BZYb electrolyte. At 600°C, the power density reached 0.38 and 0.48 W cm−2 at 0.85 and 0.75 V, respectively.

Perspectives on Cathodes for Protonic Ceramic Fuel Cells

Protonic ceramic fuel cells (PCFCs) are promising electrochemical devices for the efficient and clean conversion of hydrogen and low hydrocarbons into electrical energy. Their intermediate operation temperature (500–800 °C) proffers advantages in terms of greater component compatibility, unnecessity of expensive noble metals for the electrocatalyst, and no dilution of the fuel electrode due to water formation. Nevertheless, the lower operating temperature, in comparison to classic solid oxide fuel cells, places significant demands on the cathode as the reaction kinetics are slower than those related to fuel oxidation in the anode or ion migration in the electrolyte. Cathode design and composition are therefore of crucial importance for the cell performance at low temperature. The different approaches that have been adopted for cathode materials research can be broadly classified into the categories of protonic–electronic conductors, oxide-ionic–electronic conductors, triple-conducting oxides, and composite electrodes composed of oxides from two of the other categories. Here, we review the relatively short history of PCFC cathode research, discussing trends, highlights, and recent progress. Current understanding of reaction mechanisms is also discussed.

Regulation of Cathode Mass and Charge Transfer by Structural 3D Engineering for Protonic Ceramic Fuel Cell at 400 °C

AbstractLowering the operating temperature (ideally below 400 °C) for solid oxide fuel cell (SOFC) technology deployment has been an important transition that introduces the benefit of reduced operational costs and system durability. However, the key technical issue limiting the transition is the sluggish cathodic performance, namely the oxygen reduction reaction (ORR) rate of the conventional sponge‐like cathode dramatically drops as the temperature reduces. In this paper, 3D engineering of a cathode is conducted on a protonic ceramic fuel cell to obtain an enhanced ORR between 400 and 600 °C. Compared with a cell using a conventional sponge‐like cathode, 3D engineering improves the cathode ORR by 41% at 400 °C with a peak power density of 0.410 W cm−2. A phase field simulation is applied to assist the engineering by understanding the competition between the cathode mass and charge transfer with different cathode porosities. The results show that structural engineering of existing well‐developed cathodes is a simple and effective method to promote cathode ORR for low temperature SOFC by regulating the mass and charge transfer.

Performance Degradation in Proton-Conducting Ceramic Electrochemical Cells

Proton-conducting ceramics are a promising new class of electrochemical cells with a lower-temperature operational range in comparison to more-conventional solid-oxide or molten-carbonate counterparts. In the past, we have successfully demonstrated the scalability of this technology from the button-cell to the lab-scale stacks shown in the figure, along with strong performance and stability over thousands of hours under methane fuel at 550 ºC. This encouraging result was achieved through careful tuning of materials, fabrication procedures, and operating conditions. We have found that the degradation rates of protonic-ceramics stacks can be intense, especially at lower temperatures under fuel-cell operating mode. We have observed lower degradation rates under electrolysis operation, and at higher operating temperatures. These are both perhaps counterintuitive; lower-temperature operation is expected to improve the long-term stability, and degradation is typically more pronounced for more-common solid-oxide electrolyzers. In this presentation, we will review our studies on the root causes of performance degradation in protonic ceramics, and approaches to mitigate degradation.Previous work on performance degradation in oxygen-ion conducting electroceramics provides clues into the sources of degradation in protonic ceramics. That said, a number of degradation mechanisms are avoided by the nature of the protonic-ceramic device. For example, our microstructural characterizations reveal no nickel coarsening or agglomeration in the fuel electrode, likely due to the lower-temperature operation near 550 ºC. Operating conditions are shown to have a large impact on degradation rates in our protonic-ceramics; such conditions provide important clues about degradation’s root causes. Electrochemical Impedance Spectroscopy reveals how the slow kinetics of the electrochemical processes are closely tied to the degradation behaviors observed in our experiments.While we will continue to explore our root causes of degradation in proton-conducting electrochemical cells, we also report the impact of a gadolinium-doped ceria (GDC) interlayer on improving the durability of the cells, especially at low temperatures. This is perhaps a surprising, as GDC is a common O2--conducting material, and perhaps ill-matched to protonic ceramics. Regardless, the presence of the GDC layer at the air electrode - electrolyte interface has proven to be an effective strategy for minimizing protonic-ceramics degradation throughout our research, falling to 1.2% / 1000 hr for the methane-fueled stack at 600 ºC. While the root causes of this performance improvement remain unclear, we find the use of the GDC interlayer to impactful in reducing performance degradation in protonic ceramics. Figure 1

3D-Printing of Proton Conducting Ceramics

3D-printing technology is being extensively utilized in energy sector, as it allows for manufacturing complex structures (compacted stacks, desired microarchitectures and porosity) and customizable shapes for specific devices. Moreover, fast prototyping time and reduction of production cost make this technology promising for industrial applications. Up to now, plenty of 3D-printed energy conversion and storage devices and hence precursor materials have been proposed. Reported examples concern solar cells, biofuel cells, rechargeable ion batteries, carbon-based supercapacitors and others [1-2]. On the other hand, 3D-printing of proton-conducting materials is rarely reported. The pioneering research was presented by Mu et al., who have developed novel laser 3D-printing method which allows to obtain protonic ceramics with the desired crystal structures, microstructures, and geometries [3]. The method consists of the preparation of printable paste from component raw materials (carbonate and single metal oxides) mixed with sintering aid, the deposition of a thin green film of the targeted protonic ceramics, and the reactive sintering by rapid CO2 laser scanning. Such method was successfully applied for the synthesis of dense electrolytes (e.g. BCZYYb, BZY20), porous electrodes (e.g. BCZYYb+NiO, BaCo0.4Fe0.4Zr0.1Y0.1O3-δ), dense interconnect (La0.7Sr0.3CrO3-δ/LSC), and dense mixed protonic and electronic-conduction composite (BaCe0.85Fe0.15O3-δ– BaCe0.15Fe0.85O3-δ/BCF) [4]. The second available example is devoted to the 3D-printed proton exchange membrane and has been recently reported by K. Iwase and co-workers [5]. Scientists developed UV-cured ink (mixture of proton-conducting ionic liquids, inorganic silica nanoparticles, and UV-sensitive photocurable resins) which can be successfully applied to the printing of proton exchange membranes.In the present study, we developed 3D-printing of protonic ceramics- Ba0.5La0.5Co1-xFexO3-δ (0 ≤x≤ 1), which are promising materials for positrodes in protonic ceramic fuel cells [6]. The Project is devoted both to the construction of 3D-printer and ink preparation. Two printing technology- fused deposition modeling and extrusion-based 3D-printing were selected and embedded into one 3D-printer. In addition, the system was equipped with IR laser for post-processing. Ink (solid filament or gel) was prepared from ceramic powder and polymer (i.e. polylactic acid or polyvinyl alcohol), which act as a matrix and is removed at the end. Various compositions (e.g.ceramic to polymer ratio, polymer concentration, solvent) and synthesis conditions (e.g. time, temperature) were tested. A lot of attention was paid to the proper ceramic dispersion, which ensures printouts homogeneity. Therefore, various approaches such as ball-milling of ceramic and ultrasonication of gel were optimized and implemented. The last important step was devoted to the laser post-processing, during which polymer is removed and ceramic is sintered. Various laser powers, scan speeds and number of scans were tested. Printed layers before and after post-processing were characterized by X-Ray diffraction, Fourier Transform Infra-Red spectroscopy and Scanning Electron Microscopy. In the future it is planned to adopt developed technology and use it for the printing of multi-layered positrodes with graded functionality.

Insights into Interfacial Proton Transport in Protonic Ceramic Conductors

Understanding the mechanism of proton conduction at the interface of materials enables the development of a new generation of protonic ceramic conductors at low temperatures (< 300 °C) through water absorption and proton transport on the interface. In-situ Raman spectroscopy was performed on water-saturated, porous, and nanostructured TiO2 membranes directly observe the isotope exchange reactions suggested a Grotthuss-type proton transport and faster isotope exchange rate at 175 °C than that at 25 °C with a corresponding activation energy of 9 kJ mol-1. Comparing to traditional high-temperature protonic ceramic conductors through bulk transport, water absorption on the interface in simple oxides system has higher proton mobility and similar proton concentration, indicating the interface is a facile route for proton transport. In addition, the measured hydrogen isotope exchange rates in nanostructured BCZYYb by in-situ Raman spectroscopy in the temperature range of 100-300 °C were comparable or even higher than that in fully dense BCZYYb in the range of 400-600 °C, suggesting the possibility of using the nanostructured BCZYYb membrane as an electrolyte materials in protonic ceramic fuel cells at low temperatures (<300 °C).

Rational Identification of Doping Strategy to Achieve a Highly Conductive and Reliable Protonic Electrolyte for Electrochemical Cells

While protonic ceramics are being utilized as electrolyte materials in electrochemical cells for hydrogen or electricity production, the higher proton conductivity and chemical stability under realistic operating conditions are required to deliver fast proton flux. For widely used Y or/and Yb doped Ba(Ce,Zr)O3 electrolytes, there are still some concerns with indistinct doping mechanism and uncertain element precipitation problem during sintering, which raise practical problem on electrolyte selection. In this work, the strategy of single element doping and co-element doping has been investigated to understand how they behave differently in proton conductivity and chemical instability. Three compositions, BaCe0.4Zr0.4Y0.2O3-δ, BaCe0.4Zr0.4Yb0.2O3-δ and BaCe0.4Zr0.4Y0.1Yb0.1O3-δ, are chosen to study the overall conductivity as function of B-site environment and gas conditions to provide experimental evidences for composition optimization. More importantly, the Y or/and Yb precipitation in each composition under various sintering conditions is extensively studied to explore the safe window for sintering the electrolyte with minimal element diffusion. In addition, the diffusion of nickel element into the electrolyte grain is also studied to understand the detrimental effects on grain boundary conductivity and consequently the electrochemical performance in the cells. This study will provide some insights into protonic electrolyte selection based on technical considerations on both excellence and stability.

Proton-Conducting Ceramics for Electrochemical Ammonia Synthesis

We report our progress in developing proton-conducting ceramics for flexible storage of intermittent renewable electricity in the form of ammonia. Various electrochemical and thermochemical synthesis strategies have been investigated in pursuit of “green ammonia”. Electrochemical ammonia synthesis can harness water-splitting to source hydrogen, displacing steam-methane reforming widely used in conventional ammonia production through the well-established Haber-Bosch process (HB).This electrochemical approach potentially provides an efficient solution to the energy-storage challenges presented by the expanding market penetration of solar and wind power. The intermittent nature of these renewables presents strain on the conventional power plants tasked with stable electricity production. Through creative application of novel proton-conducting electroceramics, intermittent renewable electricity can be used to drive the synthesis of green ammonia, effectively storing electricity in the form of an easily transported, carbon-neutral, energy-dense commodity chemical. Further, the process is reversible; NH3 can be electrochemically re-converted back into electricity as needed in meeting peak load demands.Displacing Haber-Bosch proves challenging, as it requires process solutions that can simultaneously achieve high NH3 conversion and high NH3-synthesis rate while minimizing energy costs. The Haber-Bosch process achieves both through high-pressure operation (up to 300 bar), where thermodynamics are more favorable. Electrochemical systems have yet to reach this stage of technological development. All previous work has been limited to atmospheric-pressure operation, where NH3-synthesis rates are orders-of-magnitude lower. Further, most reports on electrochemical ammonia synthesis have utilized molecular H2 as the source of protons for NH3 synthesis, rather than water electrolysis as described here.In this work, we present our efforts to apply proton-conducting ceramics to enable electrochemical ammonia synthesis from H2O and N2 feedstocks. Protonic ceramics are emerging materials finding applications in efficient electricity generation, energy storage, and fuels synthesis. As shown in the figure, renewable electricity is used to drive hydrogen production through high-temperature water splitting in the protonic-ceramic electrolyzer. The hydrogen mixes with nitrogen and is then converted to NH3 over a ruthenium catalyst. The process is executed at pressures up to 12 bar, bringing significant challenges in packaging of the protonic ceramic and the catalyst. In this presentation, we review our progress in establishing pressurized operation, and the benefits it brings to electrochemical synthesis of ammonia. Figure 1

Improvement of Ni-Cermet performance of protonic ceramic fuel cells by catalyst

Generally, the NiO composite anode becomes porous after reduction. To infiltrate additional catalysts such as Pd into the NiO-composite anode before reducing NiO to Ni, a porous NiO composite anode for protonic ceramic fuel cells (PCFCs) was fabricated in this study. The porous NiO composite was fabricated by adding graphite as a pore former along with CuO as a sintering agent. The addition of graphite increased the porosity of the NiO composite anode but resulted in poor sinterability, which was addressed by adding CuO as a sintering agent to the NiO composite anode. The Pd catalyst was added to the NiO-composite anode before reducing NiO to Ni. The composite anode for PCFC with three components, namely Ni, protonic ceramics, and a Pd catalyst, was obtained by reducing NiO to Ni during the measurement. The addition of the Pd catalyst improved the anode performance in methane fuel and hydrogen fuel by enhancing the catalytic activity for the electrochemical reaction on the surface.

Electrokinetic Proton Transport in Triple (H+ /O2- /e- ) Conducting Oxides as a Key Descriptor for Highly Efficient Protonic Ceramic Fuel Cells.

Recently, triple (H+/O2−/e−) conducting oxides (TCOs) have shown tremendous potential to improve the performance of various types of energy conversion and storage applications. The systematic understanding of the TCO is limited by the difficulty of properly identifying the proton movement in the TCO. Herein, the isotope exchange diffusion profile (IEDP) method is employed via time‐of‐flight secondary ion mass spectrometry to evaluate kinetic properties of proton in the layered perovskite‐type TCOs, PrBa0.5Sr0.5Co1.5Fe0.5O5+ δ (PBSCF).Within the strategy, the PBSCF shows two orders of magnitude higher proton tracer diffusion coefficient (D * H, 1.04 × 10−6 cm2 s−1 at 550 °C) than its oxygen tracer diffusion coefficient at even higher temperature range (D * O, 1.9 × 10−8 cm2 s−1 at 590 °C). Also, the surface exchange coefficient of a proton (k*H) is successfully obtained in the value of 2.60 × 10−7 cm s−1 at 550 °C. In this research, an innovative way is provided to quantify the proton kinetic properties (D * H and k*H) of TCOs being a crucial indicator for characterizing the electrochemical behavior of proton and the mechanism of electrode reactions.

Continuous hydrothermal synthesis in supercritical conditions as a novel process for the elaboration of Y-doped BaZrO3

The present work describes a novel process for the elaboration of a ceramic material. Y-doped barium zirconate, an electrolyte material for Protonic Ceramic Fuel cell, was synthesized by a continuous hydrothermal process in supercritical conditions (410 °C/30.0 MPa) using nitrate precursors and NaOH reactants. The use of supercritical water allowed the formation of particles of about 50 nm in diameter with a narrow size distribution. X-Ray Diffraction examination revealed that a major perovskite phase with few BaCO3 and YO(OH) impurities was obtained. BaCO3 is assumed to form due to faster kinetics than Y-doped BaZrO3 resulting in a Ba-deficient perovskite phase. The Ba-deficiency limits the incorporation of yttrium into the perovskite structure. However, a thermal treatment at 1000 °C for 1 h allows to homogenize the composition and thus to obtain the compound Ba1.01Zr0.85Y0.15O3-δ.

Percolation Micro-Model to Predict the Electrochemical Properties of Composite Anode and Cathode in Protonic Ceramic Fuel Cell

Percolation Micro-Model to Predict the Electrochemical Properties of Composite Anode and Cathode in Protonic Ceramic Fuel Cell

Moderate temperature sintering of BaZr0.8Y0.2O3-δ protonic ceramics by A novel cold sintering pretreatment

The state-of-the-art protonic ceramic conductor BaZr0.8Y0.2O3-δ (BZY20) requires an extremely high sintering temperature (≥1700 °C) to achieve the desired relative density and microstructure necessary to function as a proton conducting electrolyte. In this work, we developed a cold sintering pretreatment assisted moderate-temperature sintering method for the fabrication of high-quality pure BZY20 pellets. BZY20 pellets with high relative density of ~94% were fabricated with a final sintering temperature of 1500 °C (200 °C lower than the traditional sintering temperature). A comparison with BZY20 control samples indicated that the proper amount of BaCO3 introduced on the BZY20 particle surface and the high green density achieved by cold sintering pretreatment were the main drivers for lowering the sintering temperature. The electrical conductivity measurement by electrochemical impedance spectroscopy showed that the as-prepared BZY20 pellets have a proton conductivity comparable to the state-of-the-art values. The cold sintering pretreatment outlined in this work has the potential to lower the sintering temperatures for similar types of protonic ceramic materials under consideration for a wide range of energy conversion and storage applications.