Perspectives on Cathodes for Protonic Ceramic Fuel Cells

Nickel-Regulated Composite Cathode with Balanced Triple Conductivity for Proton-Conducting Solid Oxide Fuel Cells

Proton-conducting solid oxide fuel cells (H-SOFCs) have the potential to be a promising technology for energy conversion and storage. To achieve high chemical compatibility and catalytic activity, nickel-doped barium ferrate with triple conducting ability is developed as cathodes for H-SOFCs, presenting an impressive electrochemical performance at intermediate temperatures. The cell performance with the optimized BaCe0.26 Ni0.1 Fe0.64 O3 -δ (BCNF10) composite cathode reaches an outstanding performance of 1.04 W cm-2 at 600 °C. The high electrocatalytic capacity of the nickel-doped barium ferrate cathode can be attributed to its significant proton conductivity which is confirmed through hydrogen permeation experiments. Density functional theory (DFT) calculations are further conducted to reveal that the presence of nickel can enhance processes of hydration formation and proton migration, leading to improve proton conductivity and electro-catalytic activity.

Proton Transport in the Gadolinium-Doped Layered Perovskite BaLaInO4

Materials capable for use in energy generation have been actively investigated recently. Thermoelectrics, photovoltaics and electronic/ionic conductors are considered as a part of the modern energy system. Layered perovskites have many attractions, as materials with high conductivity. Gadolinium-doped layered perovskite BaLaInO4 was obtained and investigated for the first time. The high values of conductivity were proved. The composition BaLa0.9Gd0.1InO4 demonstrates predominantly protonic transport under wet air and low temperatures (<400 °C). The doping by rare earth metals of layered perovskite is a prospective method for significantly improving conductivity.

Direct Electrophoretic Deposition and Characterization of Thin-Film Membranes Based on Doped BaCeO3 and CeO2 for Anode-Supported Solid Oxide Fuel Cells

In this work, a technology was developed for the formation of BaCe0.8Sm0.2O3+1 wt% CuO (BCS-CuO)/Ce0.8Sm0.2O1.9 (SDC) thin-film electrolyte membranes for intermediate-temperature solid oxide fuel cells (IT-SOFCs) on porous NiO-BCS-CuO anode substrates using direct electrophoretic deposition (EPD). The effect of increasing the zeta potential when modifying the base suspension of a micro-sized SDC-gn powder (glycine–nitrate method) with the addition of a SDC-lec nanopowder (laser evaporation–condensation) was investigated. Dependences of the current strength on the deposition time and the deposited weight on the EPD voltage were obtained, and evolution of the morphology of the coatings during the modification of the SDC-gn suspension and a suspension of BCS-CuO powder was studied. The compatibility of the shrinkage kinetics of the SDC, the BCS-CuO electrolyte coatings and the NiO-BCS-CuO anode substrate was studied during the high-temperature sintering. Dense BCS-CuO/SDC films of different thicknesses were obtained for the first time on porous NiO-BCS-CuO anode substrates and comprehensive microstructural and electrochemical studies were carried out. The developed technology can be applied to the formation of anode-supported SOFCs with thin-film electrolyte membranes.

Multi-Physical and Electrochemical Coupling Model for the Protonic Ceramic Fuel Cells with H+/e−/O2− Mixed Conducting Cathodes

A protonic ceramic fuel cell (PCFC) has great potential for medium temperature power generation. Its working process, however, is complicated and quite different from the traditional oxygen ionic solid oxide fuel cell (O2−-SOFC) and proton exchange membrane fuel cell (PEMFC). In this paper, a multi-physical model for the PCFC with H+/e−/O2− mixed conducting cathode is established, in which the fuel- and oxidant-diffusing processes; electron-, oxygen ion-, and proton-conducting processes; three electrochemical reactions; and their coupling working details are carefully considered. Taking Ni-BZCY/BZCY/BZCY-LSCF PCFC as an example, the validation of the model is well verified by good agreements with the experiment iop-Vop curves at different temperatures. The result shows that the cathodic electrochemical reactions will be concentrated to a small thickness near the electrolyte because of the greatly decreased ionic conductivity compared with the high electronic conductivity at an intermediate temperature. O2− within the PCFC cathode is only an intermediate transform substance between the electrons and protons. Thus, there is a peak oxygen ion current distribution within the composite cathode of PCFC. The cathodic oxygen reduction half reaction is found to be a key factor to dominate the total PCFC voltage loss at the intermediate temperature zone. The concentration polarization of anode-supported PCFC is small, due to the vapors that are generated in the cathode side instead of anode side.

High-Temperature Behavior, Oxygen Transport Properties, and Electrochemical Performance of Cu-Substituted Nd1.6Ca0.4NiO4+δ Electrode Materials

In this study, Nd1.6Ca0.4Ni1−yCuyO4+δ-based electrode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) are investigated. Materials of the series (y = 0–0.4) are obtained by pyrolysis of glycerol-nitrate compositions. The study of crystal structure and high-temperature stability in air and under low oxygen partial pressure atmospheres are performed using high-resolution neutron and in situ X-ray powder diffraction. All the samples under the study assume a structure with Bmab sp.gr. below 350 °C and with I4/mmm sp.gr. above 500 °C. A transition in the volume thermal expansion coefficient values from 7.8–9.3 to 9.1–12.0 × 10−6, K−1 is observed at approximately 400 °C in air and 500 °C in helium.The oxygen self-diffusion coefficient values, obtained using isotope exchange, monotonically decrease with the Cu content increasing, while concentration dependence of the charge carriers goes through the maximum at x = 0.2. The Nd1.6Ca0.4Ni0.8Cu0.2O4+δ electrode materialdemonstrates chemical compatibility and superior electrochemical performance in the symmetrical cells with Ce0.8Sm0.2O1.9, BaCe0.8Sm0.2O3−δ, BaCe0.8Gd0.19Cu0.1O3−δ and BaCe0.5Zr0.3Y0.1Yb0.1O3−δ solid electrolytes, potentially for application in IT-SOFCs.

Unusual Lattice Parameters Behavior for La1.9Ca0.1NiO4+δ at the Temperatures below Oxygen Loss

In this work, we studied the structural features of La1.9Ca0.1NiO4.11, which is considered a promising cathode material for intermediate temperature solid-oxide fuel cells (IT-SOFC). The effect of different pretreatments on the structural characteristics of the sample was studied using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) in order to elucidate the origin of a peculiar change of lattice parameters observed earlier during in situ XRD studies. The XRD studies have shown that anisotropic broadening for reflections with a high Miller index l appears after tempering of a quenched (from 1100 °C) sample at 250 °C. This temperature is too low for the release/incorporation of oxygen into the structure but is sufficient for oxygen migration inside the structure. The HRTEM assisted us in revealing differences in the defect structure after different pretreatments. Based on obtained results, the following possible explanation was proposed. Observed additional microstrains and non-oriented planar defects as well as a decrease in the coherent scattering region size in the [00l] direction are caused by the non-homogeneous redistribution of interstitial oxygen in the structure during tempering.

Slip Casting and Solid-State Reactive Sintering of BCZY(BaCexZr0.9−xY0.1O3−d)-NiO/BCZY Half-Cells

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.

Layered Oxygen-Deficient Double Perovskites as Promising Cathode Materials for Solid Oxide Fuel Cells

Development of new functional materials with improved characteristics for solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs) is one of the most important tasks of modern materials science. High electrocatalytic activity in oxygen reduction reactions (ORR), chemical and thermomechanical compatibility with solid electrolytes, as well as stability at elevated temperatures are the most important requirements for cathode materials utilized in SOFCs. Layered oxygen-deficient double perovskites possess the complex of the above-mentioned properties, being one of the most promising cathode materials operating at intermediate temperatures. The present review summarizes the data available in the literature concerning crystal structure, thermal, electrotransport-related, and other functional properties (including electrochemical performance in ORR) of these materials. The main emphasis is placed on the state-of-art approaches to improving the functional characteristics of these complex oxides.