Electrospinning of porous fibrous electrode materials for solid oxide fuel cells: fundamentals and challenges

Background

Solid oxide fuel cells (SOFCs) are high-temperature electrochemical devices that convert the chemical energy of fuels directly into electrical energy with high conversion efficiency. SOFCs can use a variety of fuels, including hydrogen and hydrocarbons, to provide electricity for residential, industrial or transportation applications. SOFCs consist of a porous cathode, a dense electrolyte layer and a porous anode. The two porous electrodes provide gas transport pathways, active sites for electrochemical reactions, and paths for ions and electrons required for the reactions.

The main point of this paper

Balance between operating temperature and performance:

Increasing the operating temperature can improve electrochemical performance, but may reduce durability; lowering the operating temperature can improve durability and reduce material costs, but may reduce the ionic conductivity of the electrolyte and increase interface resistance

Advances in electrode preparation technology:

The maximum power density (MPD) and durability of SOFCs have been significantly improved by enhancing the microstructure and performance of the cathode. For example, the cathode was prepared by co-sputtering (La0.6Sr0.4)0.98CoO3 and (Gd0.2Ce0.8) alloy, and the MPD was 2.56 and 3.01 W cm−2 at 600℃ and 650℃, respectively

Development of composite cathode:

La0.6Sr0.4CoO3−δ (LSC) was impregnated in the laser sintered Ce0.9Gd0.1O2−δ (GDC) framework to prepare the composite cathode, and the SOFC with MPD of 2.24 W cm−2 was obtained at 750℃, and the performance did not decrease within 50 h

Thermal expansion coefficient (TEC) mismatch problem:

Adding 20% ​​Sm0.85Zn0.15MnO3 to SrNb0.1Co0.9O3-δ (SNC) cathode (SZM), the obtained SNC-SZM composite cathode has good thermal expansion performance matching the electrolyte GDC. At 700°C, the cathode polarization resistance (Rp) is 0.012 Ω cm2, the MPD of a single cell is 1.22 W cm−2, and it works stably for 120 h at 0.8 a cm−2

Application of electrospinning technology:

Preparing fiber cathodes by electrospinning or introducing more nanoactive sites on the cathode frame by impregnation can further improve the performance of the electrode. SOFC using composite fiber cathodes has significantly improved battery performance durability.

Application progress and challenges of electrospinning technology in solid oxide fuel cells

Advantages of electrospinning:

Electrospinning technology is conducive to the preparation of high-porosity SOFCs fiber electrodes, which have high triple-phase boundary density and electrochemical activity

Combined with impregnation process:

When electrospinning is combined with impregnation process, unique electrode structures can be further created to improve the output power and durability of the battery

Challenges of production efficiency and electrode preparation process:

Electrospinning to produce fiber electrodes is limited by production efficiency and subsequent electrode preparation processes (such as calcination, grinding and sintering), which may lead to the destruction of continuous fiber morphology

Maintaining the continuous morphology of fibers:

Maintaining the continuous fiber morphology inside the electrode is a hot topic of research, which is crucial to improving electrode performance

Porosity and durability of fiber electrodes:

The porosity and durability of fiber electrodes are explored, which are crucial to the long-term stability and performance of batteries

Summarize

Electrospinning technology is of great significance in the preparation of high-performance porous electrodes for solid oxide fuel cells (SOFCs). This paper reviews the basic knowledge of electrospinning for preparing porous materials, analyzes the effects of key spinning parameters on fiber properties, and focuses on the challenges of electrospinning for preparing SOFC electrode materials, including improving production efficiency and avoiding damage to the fiber structure morphology. Important literature data on SOFC fiber cathodes and anodes in recent years are summarized, covering topics such as electrode porosity and long-term battery performance.

According to the literature review, in the past decade, electrospinning has improved the performance of SOFC electrode materials, especially cathode materials, which has helped to increase the maximum output power of the battery to 1-3 W cm−2 in the medium temperature range.