Search Results (12)

Proton-conducting ceramics have gained significant attention in various applications. Yttrium-doped barium cerium zirconate (BaCe_xZr_1−x−yY_yO_3–δ) is the state-of-the-art proton-conducting electrolyte but poses a major challenge because of its high sintering temperature. Sintering aids have been found to substantially reduce the sintering temperature of BaCe_xZr_1−x−yY_yO_3–δ. This work evaluates, for the first time, the impact of NiO and ZnO addition in three different loadings (1, 3, 5 mol%), via wet mechanical mixing, on the sintering and electrical properties of a low cerium-containing composition, BaCe_0.2Zr_0.7Y_0.1O_3–δ (BCZY). The sintering temperature remarkably dropped from 1600 °C (for pure BCZY) to 1350 °C (for NiOBCZY and ZnOBCZY) while achieving > 95% densification. In general, ZnO gave higher densification than NiO, the highest being 99% for 5 mol% ZnOBCZY. Dilatometric studies revealed that ZnOBCZY attained complete shrinkage at temperatures lower than NiOBCZY. Up to 650 °C, ZnO showed higher conductivity compared to NiO for the same loading, mostly due to a higher extent of Zn incorporation inside the BCZY lattice as seen from the BCZY peak shift to a lower Bragg’s angle in X-ray diffractograms, and the bigger grain sizes of ZnO samples compared to NiO captured in scanning electron microscopy. At any temperature, the variation in conductivity as a function of sintering aid concentration followed the orders 1 mol% > 3 mol% > 5 mol% (for ZnO) and 1 mol% < 3 mol%~5 mol% (for NiO). This difference in conductivity trends has been attributed to the fact that Zn fully dissolves into the BCZY matrix, unlike NiO which mostly accumulates at the grain boundaries. At 600 °C, 1 mol% ZnOBCZY showed the highest conductivity of 5.02 mS/cm, which is, by far, higher than what has been reported in the literature for a Ce/Zr molar ratio <1. This makes ZnO a better sintering aid than NiO (in the range of 1 to 5 mol% addition) in terms of higher densification at a sintering temperature as low as 1350 °C, and higher conductivity. Full article

Proton-conducting ceramic materials have emerged as effective candidates for improving the performance of solid oxide cells (SOCs) and electrolyzers (SOEs) at intermediate temperatures. BaCeO₃ and BaZrO₃ perovskites doped with rare-earth elements such as Y₂O₃ (BCZY) are well known for their high proton conductivity, low operating temperature, and chemical stability, which lead to SOCs’ improved performance. However, the high sintering temperature and extended processing time needed to obtain dense BCZY-type electrolytes (typically > 1350 °C) to be used as SOC electrolytes can cause severe barium evaporation, altering the stoichiometry of the system and consequently reducing the performance of the final device. The cold sintering process (CSP) is a novel sintering technique that allows a drastic reduction in the sintering temperature needed to obtain dense ceramics. Using the CSP, materials can be sintered in a short time using an appropriate amount of a liquid phase at temperatures < 300 °C under a few hundred MPa of uniaxial pressure. For these reasons, cold sintering is considered one of the most promising ways to obtain ceramic proton conductors in mild conditions. This review aims to collect novel insights into the application of the CSP with a focus on BCZY-type materials, highlighting the opportunities and challenges and giving a vision of future trends and perspectives. Full article

Ceramic proton conductors have the potential to lower the operating temperature of solid oxide cells (SOCs) to the intermediate temperature range of 400–600 °C. This is attributed to their superior ionic conductivity compared to oxide ion conductors under these conditions. However, prominent proton-conducting materials, such as yttrium-doped barium cerates and zirconates with specified compositions like BaCe_1−xY_xO_3−δ (BCY), BaZr_1−xY_xO_3−δ (BZY), and Ba(Ce,Zr)_1−yY_yO_3−δ (BCZY), face significant challenges in achieving dense electrolyte membranes. It is suggested that the incorporation of transition and alkali metal oxides as sintering additives can induce liquid phase sintering (LPS), offering an efficient method to facilitate the densification of these proton-conducting ceramics. However, current research underscores that incorporating these sintering additives may lead to adverse secondary effects on the ionic transport properties of these materials since the concentration and mobility of protonic defects in a perovskite are highly sensitive to symmetry change. Such a drop in ionic conductivity, specifically proton transference, can adversely affect the overall performance of cells. The extent of variation in the proton conductivity of the perovskite BCZY depends on the type and concentration of the sintering aid, the nature of the sintering aid precursors used, the incorporation technique, and the sintering profile. This review provides a synopsis of various potential sintering techniques, explores the influence of diverse sintering additives, and evaluates their effects on the densification, ionic transport, and electrochemical properties of BCZY. We also report the performance of most of these combinations in an actual test environment (fuel cell or electrolysis mode) and comparison with BCZY. Full article

A ternary Ni–BaCe_0.9Y_0.1O₃ (BCY)–Ce_0.9Gd_0.1O₂ (GDC) cermet involving 40 vol% Ni was fabricated, and its hydrogen permeation characteristics were evaluated when the GDC volume fraction was varied from 0 to 30 vol%. The X-ray diffraction results of the cermet after sintering at 1400 °C revealed that GDC was dissolved in BCY when the GDC volume composition was 20 vol%. Regardless of the BCY and GDC volume fractions, the metal conductivity of the cermet was dominated by Ni. After the addition of only 1 vol% GDC, the particle sizes of Ni and BCY in the cermet significantly decreased, and the particle size decreased as the volume fraction of GDC increased. The hydrogen permeability increased with increasing temperature and for up to 10 vol% GDC, and a maximum permeation rate of 0.142 mL min⁻¹ cm⁻² was obtained at 700 °C. This value is comparable to or better than previously reported values for Ni-cermets under the same conditions. The amount of hydrogen permeation decreased above 10 vol% GDC. This study demonstrated that Ni-BCY-GDC cermet is a material that has both high hydrogen permeability and CO₂ resistance. Full article

Proton ceramic fuel cells offer numerous advantages compared with conventional fuel cells. However, the practical implementation of these cells is hindered by the poor sintering activity of the electrolyte. Despite extensive research efforts to improve the sintering activity of BCZY, the systematic exploration of the utilization of NiO as a sintering additive remains insufficient. In this study, we developed a novel BaCe_0.55Zr_0.35Y_0.1O_3-δ (BCZY) electrolyte and systematically investigated the impact of adding different amounts of NiO on the sintering activity and electrochemical performance of BCZY. XRD results demonstrate that pure-phase BCZY can be obtained by sintering the material synthesized via solid-state reaction at 1400 °C for 10 h. SEM analysis revealed that the addition of NiO has positive effects on the densification and grain growth of BCZY, while significantly reducing the sintering temperature required for densification. Nearly fully densified BCZY ceramics can be obtained by adding 0.5 wt.% NiO and annealing at 1350 °C for 5 h. The addition of NiO exhibits positive effects on the densification and grain growth of BCZY, significantly reducing the sintering temperature required for densification. An anode-supported full cell using BCZY with 0.5 wt.% NiO as the electrolyte reveals a maximum power density of 690 mW cm⁻² and an ohmic resistance of 0.189 Ω cm² at 650 °C. Within 100 h of long-term testing, the recorded current density remained relatively stable, demonstrating excellent electrochemical performance. Full article

Cermet films consisting of Ni, BaCe_0.4Zr_0.4Y_0.2O_3−δ (BCZY), and Gd_0.1Ce_0.9O_x (GDC), specifically, 60 wt%Ni–BCZY, 60 wt%Ni–BCZY–GDC, and 60 wt%Ni–GDC, were formed on BCZY electrolyte supports as anodes of proton ceramic fuel cells (PCFCs). The Ni grain size in these films after sintering at 1450 °C was around 2 μm. The GDC addition did not affect the Ni grain size in the case of the BCZY matrix. The anodic properties greatly depended on the oxide phase composition and worsened with increasing the GDC content. This probably occurred because of the addition of GDC, which has low proton conductivity and inhibited the proton conduction path of BCZY, reducing three-phase boundaries in the anode bulk. Since BCZY has a lower grain growth rate during sintering than BaCe_0.8Y_0.2O_3−δ, the Ni grain growth was likely suppressed by the surrounding Ni grains containing small BCZY grains. Full article

Understanding the impact of sintering temperature on the physical and chemical properties of Ni-BaCe_0.54Zr_0.36Y_0.1O_3-δ (Ni-BCZY) composite anode is worthy of being investigated as this anode is the potential for protonic ceramic fuel cell (PCFC) application. Initially, NiO–BCZY composite powder with 50 wt% of NiO and 50 wt% of BCZY is prepared by the sol–gel method using citric acid as the chelating agent. Thermogravimetric analysis indicates that the optimum calcination temperature of the synthesised powder is 1100 °C. XRD result shows that the calcined powder exists as a single cubic phase without any secondary phase with the lattice parameter (a) of 4.332 Å. FESEM analysis confirms that the powder is homogeneous and uniform, with an average particle size of 51 ± 16 nm. The specific surface area of the calcined powder measured by the Brunauer–Emmett–Teller (BET) technique is 6.25 m²/g. The thickness, porosity, electrical conductivity and electrochemical performance of the screen-printed anode are measured as a function of sintering temperature (1200–1400 °C). The thickness of the sintered anodes after the reduction process decreases from 28.95 μm to 26.18 μm and their porosity also decreases from 33.98% to 26.93% when the sintering temperature increases from 1200 °C to 1400 °C. The electrical conductivities of the anodes sintered at 1200 °C, 1300 °C and 1400 °C are 443 S/cm, 633 S/cm and 1124 S/cm at 800 °C, respectively. Electrochemical studies showed that the anode sintered at 1400 °C shows the lowest area specific resistance (ASR) of 1.165 Ω cm² under a humidified (3% H₂O) gas mixture of H₂ (10%) and N₂ (90%) at 800 °C. Further improvement of the anode’s performance can be achieved by considering the properties of the screen-printing ink used for its preparation. Full article

Hydrogen is expected to play an important role in the near future in the transition to a net-zero economy. Therefore, the development of new in situ and real-time analytical tools able to quantify hydrogen at high temperatures is required for future applications. Potentiometric sensors based on perovskite-structured solid-state electrolytes can be a good option for H₂ monitoring. Nevertheless, the geometry of the sensor should be designed according to the specific necessities of each technological field. Conventional shaping processes need several iterations of green shaping and machining to achieve a good result. In contrast, 3D printing methods stand out from conventional ones since they simplify the creation of prototypes, reducing the cost and the number of iterations needed for the obtainment of the final design. In the present work, BaCe_0.6Zr_0.3Y_0.1O_3-α (BCZY) was used as a proton-conducting electrolyte for potentiometric sensors construction. Two different shapes were tested for the sensors’ electrolyte: pellets (BCZY-Pellet) and crucibles (BCZY-Crucible). Ceramics were shaped using extrusion-based 3D printing. Finally, parameters, such as sensitivity, response time, recovery time and the limit of detection and accuracy, were evaluated for both types of sensors (BCZY-Pellet and BCZY-Crucible) at 500 °C. Full article

This study reports on the structure analyses of NiO-BCZY (BCZY = BaCe_0.54Zr_0.36Y_0.1O_3-δ) anode composite materials with the ratio of 50:50 for proton ceramic fuel cells (PCFCs) application. A product of sintered NiO-BCZY was developed to understand the structural properties of the anode materials. The objectives of this work were (a) to investigate the lattice expansion of the anode by using a high-temperature XRD (HT-XRD) from 400–700 °C; and (b) to calculate the crystallite size of the sample by using Scherrer’s and Williamson Hall’s methods. The results obtained from the HT-XRD revealed that the diffraction peaks of NiO and BCZY are matched with the cubic phase perovskite structure. For example at T = 400 °C, the lattice parameter of NiO is a = 4.2004 Å and BCZY is a = 4.3331 Å. The observation also showed that the lattice expansion increased with the temperature. Furthermore, analyses of the Scherrer and Williamson Hall methods, respectively, showed that the crystallite size is strongly correlated with the lattice expansion, which proved that the crystallite size increased as the operating temperature increased. The increment of crystallite size over the operating temperature contributed to the increment of conductivity values of the single cell. Full article

BaCe_0.2Zr_0.6Y_0.2O_3−δ (BCZY) perovskite electrolytes were synthesized for intermediate-temperature solid oxide fuel cell with a cost-effective and versatile co-precipitation method. The synthesized BCZY electrolytes were sintered at 900, 1000, and 1100 °C to observe the effects of low sintering temperature on the structural, morphological, thermal, and electrical properties of BCZY. All BCZY electrolytes materials exhibited a crystalline perovskite structure and were found to be thermally stable. The crystallinity and conductivity of BCZY electrolyte enhanced with increased sintering temperature, due to the grain growth. At the same time, secondary phases of carbonates were also observed for samples sintered at a temperature lower than 1100 °C. The BCZY sintered at 1100 °C exhibited a density >95%, and a power density of 350 mWcm⁻² with open-circuit voltage 1.02 V at 650 °C was observed due its dense and airtight structure. Based on the current investigation, we suggest that the BaCe_0.2Zr_0.6Y_0.2O_3−δ perovskite electrolyte sintered at a temperature of 1100 °C is a suitable electrolyte for IT-SOFC. Full article

Slip casting was used to prepare BaCe_xZr_0.9−xY_0.1O_3−d(BCZY)-NiO tubes with a diameter of ½ inches (1.25 cm) and ¾ inches (1.875 cm). Two compositions were studied: BCZY18 and BCZY27 for x = 0.1 and 0.2, respectively. The unfired tubes were then dip-coated with three layers of the BCZY electrolyte membrane. Solid-state reactive sintering was used, meaning that the support and membrane were prepared with the precursors (oxides and carbonates). After co-sintering at 1550 °C, a 20-micron thick dense BCZY layer was well-adhered to the 1 mm thick BCZY-NiO support, as confirmed by scanning electron microscopy. The sintered BCZY-NiO/BCZY tubes were sealed onto alumina or BCZY substrates using a silver-based braze (with TiO₂ and CuO additions). Gas tightness was achieved under 2 bar when covering the silver braze with a ceramic (Resbond) sealing layer. These slip cast tubes are intended for use as hydrogen electrodes in various protonic ceramic devices, and the advantages of short tubes for reactor design are discussed. Full article

Three polyimides and six inorganic fillers in a form of nanometer-sized particles were studied as thick film solution cast mixed matrix membranes (MMMs) for the transport of CO₂, CH₄, and H₂O. Gas transport properties and electron microscopy images indicate good polymer-filler compatibility for all membranes. The only filler type thatdemonstrated good distribution throughout the membrane thickness at 10 wt.% loading was BaCe_0.2Zr_0.7Y_0.1O₃ (BCZY). The influence of this filler on MMM gas transport properties was studied in detail for 6FDA-6FpDA in a filler content range from one to 20 wt.% and for Matrimid^® and P84^® at 10 wt.% loading. The most promising result was obtained for Matrimid^®—10 wt.% BCZY MMM, which showed improvement in CO₂ and H₂O permeabilities accompanied by increased CO₂/CH₄ selectivity and high water selective membrane at elevated temperatures without H₂O/permanent gas selectivity loss. Full article