High-performing and stable non-doped ceria electrolyte with amorphous carbonate coating layer for low-temperature solid oxide fuel cells

In Situ Phase-Transformation Forming a Bicontinuous (Ni, Co, Ti, and Al)-Oxide/Li2CO3 Interpenetrating Network Electrolyte for Solid Oxide Fuel Cells

Designing heterogeneous electrolytes with superior interface charge transfer is promising for low-temperature solid oxide fuel cells (LT-SOFCs). However, a rational construction with optimal interfaces to maximize ionic conduction remains a challenge. Here an in situ phase-transformation strategy is demonstrated to prepare a highly conductive heterogeneous electrolyte. A pristine LiNiO2-TiO2 nanocomposite precursor undergoes chemical reactions and phase-transformation upon heating and feeding H2, destroying the original phases, and forming new species, including an amorphous Li2CO3 scaffold within a (Ni, Co, Al, and Ti)-oxide (NCAT) matrix. It creates an intertwining and continuous network inside the electrolyte with plentiful interfaces. The in situ formed NCAT/Li2CO3 heterogeneous electrolyte displays superior ionic conductivity and impressive fuel cell performance. This work emphasizes the potential of rational heterogeneous structure design and interface engineering for LT-SOFC electrolyte through an in situ phase-transform approach. The generated interfaces enhance ion transport, presenting an opportunity for further optimizing electrolyte candidates, and lowering the operating temperatures of SOFCs.

Enabling fast ionic transport in CeO2-La1-2xBaxBixFeO3 nanocomposite electrolyte for low temperature solid oxide fuel cell application

Recent studies indicate that electrolyte ionic conductivity plays a pivotal role in reducing the operating temperature of solid oxide fuel cells (SOFCs). In this regard, nanocomposite electrolytes have drawn significant attention owing to their enhanced ionic conductivity and fast ionic transport. In this study, we fabricated CeO₂-La_1-2xBa_xBi_xFeO₃ nanocomposites and tested them as a high-performance electrolyte for low-temperature solid oxide fuel cells (LT-SOFCs). The prepared samples were characterized by their phase structure, surface, and interface property via transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS), followed by being applied in SOFCs to examine their electrochemical performance. In the fuel cells, it was found that the optimal composition 90CeO₂-10La_1-2xBa_xBi_xFeO₃ electrolyte-based SOFC delivered a peak power density of 834 mW cm^-2 along with an open circuit voltage (OCV) of 1.04 V at 550 °C. A comparative study revealed that the nanocomposite electrolyte exhibited a total conductivity of 0.11 S cm^-1 at 550 °C. Moreover, the rectification curve manifested the formation of the Schottky junction, suppressing the electronic conduction. This study conclusively shows that the addition of La_1-2xBa_xBi_xFeO₃ (LBBF) into ceria electrolyte is a viable approach for constructing high-performance electrolytes for LT-SOFCs.

Toward next-generation fuel cell materials

The fuel cell's three layers-anode/electrolyte/cathode-convert fuel's chemical energy into electricity. Electrolyte membranes determine fuel cell types. Solid-state and ceramic electrolyte SOFC/PCFC and polymer based PEMFC fuel cells dominate fuel cell research. We present a new fuel cell concept using next-generation ceramic nanocomposites made of semiconductor-ionic material combinations. A built-in electric field driving mechanism boosts ionic (O^2- or H⁺ or both) conductivity in these materials. In a fuel cell device, non-doped ceria or its heterostructure might attain 1 Wcm^-2 power density. We reviewed promising functional nanocomposites for that range. Ceria-based and multifunctional semiconductor-ionic electrolytes will be highlighted. Owing to their simplicity and abundant resources, these materials might be used to make fuel cells cheaper and more accessible.

High-performing and stable semiconductor yttrium-doped gadolinium electrolyte for low-temperature solid oxide fuel cells

High-performing electrolytes at low operating temperatures have become an inevitable trend in the development of low-temperature solid oxide fuel cells (LT-SOFCs). Such electrolytes have drawn significant attention due to their appeal for high performance. Herein, we propose a new material by doping Y³⁺ into Gd₂O₃ for LT-SOFC electrolyte use. The prepared material was characterized in terms of crystal structure, surface, and interface properties, followed by its application in LT-SOFCs. YDG delivered promising SOFC performance with a power density of 1046 mW cm^-2 at 550 °C along with high ionic conductivity of 0.19 S cm^-1. Moreover, impedance spectra revealed that YDG exhibited the least ohmic resistance of 0.06-0.09 Ω cm² at 550-460 °C. Furthermore, stable operation for 60 h demonstrated the chemical stability of the material in reduced temperature environments. Density function theory was also applied to analyze the electronic band structure and density of states of the synthesized sample. Our findings thus certify that YDG as a high-performing electrolyte at low operating temperatures.

Novel n-i CeO2/a-Al2O3 Heterostructure Electrolyte Derived from the Insulator a-Al2O3 for Fuel Cells

Heterostructure technologies have been regarded as promising methods in the development of electrolytes with high ionic conductivity for low-temperature solid oxide fuel cells (LT-SOFCs). Here, a novel semiconductor/insulator (n-i) heterostructure strategy has been proposed to develop composite electrolytes for LT-SOFCs based on CeO₂ and the insulator amorphous alumina (a-Al₂O₃). The constructed CeO₂/a-Al₂O₃ electrolyte exhibits an ionic conductivity of up to 0.127 S cm^-1, and its fuel cell achieves a maximum power density (MPD) of 1017 mW cm^-2 with an open-circuit voltage (OCV) of 1.14 V at 550 °C without the short-circuiting problem, suggesting that the introduction of a-Al₂O₃ can effectively suppress the electron conduction of CeO₂. It is found that the potential energy barrier at the heterointerfaces caused by the ultrawide band gap of the insulator a-Al₂O₃ plays an important role in restraining electron conduction. Simultaneously, the thermoelectric effect of the insulator induces more oxygen vacancies because of interface charge compensation, which further promotes ionic transport and results in high ionic conductivity and fuel cell performance. This study presents a practical n-i heterostructure electrolyte design, and further research confirmed the advanced functionality of the CeO₂/a-Al₂O₃ electrolyte. Our study may open frontiers in the field of developing high-efficiency electrolytes of LT-SOFCs using insulating materials such as amorphous alumina.

Unveiling the role of lithium in cerium oxide based ceramic fuel cells employing lithium compounds as the anode

Cerium oxide based ceramic fuel cells (CFCs) enable a good cell performance with high ionic conductivity when a lithium compound is utilized as the anode material. However, the mechanism of enhancement of the ionic conductivity and its effect on the fuel cell performance as well as the stability involved via the lithium effect have not been fully understood in this stage. In this paper, the role of lithium was unveiled through experimental measurements and DFT calculations in cerium oxide-based CFCs. It is found that the redistribution of lithium in cerium oxide causes gradient Li⁺ distribution, resulting in the diffusion of Li⁺ in CeO₂ electrolyte to improve the cell performance. Further study discloses that the lithium at the anode is depleted and in situ doped into the cerium oxide lattice, modulating the band structure of CeO₂, leading to the increased electronic conductivity and open circuit voltage (OCV) degradation. This work provides an insight into the role of lithium in cerium oxide-based CFCs, opening a new methodology for designing high performance CFCs.