Rational design of nickel-based perovskite-type cathode for improved performance of protonic ceramic fuel cells

Abstract

Protonic ceramic fuel cells (PCFCs) are highly efficient and promising de-vices for energy conversion, offering a way to transform chemical energy directly into electricity. PCFCs operate at a temperature range 550-700 °C. However, PCFCs face numerous challenges. One of the most significant challenges is the slow oxygen reduction reaction (ORR) kinetics. Additionally, protons react with oxygen to produce water at the cathode. Thus, proton transfer is also necessary for cathode. To accelerate ORR kinetics and proton transfer of cathodes simultaneously, traditional perovskite materi-als are modified and optimized in this work. Some improvements have been achieved:

Ni-doped La0.5Sr0.5MnO3-δ (LSM) cathode was synthesized with glycine sol-gel technique. The PCFC with La0.5Sr0.5Mn0.9Ni0.1O3-δ (LSMNi) cathode delivers a peak power density (Pmax) of 1.1 W cm-2 at 700 °C compared to LSM cathode (788 mW cm-2). LSMNi as cathode demonstrates promising stability over 220 h. Simulation results revealed Ni doping LSM cathode accelerated in both ORR kinetics and proton transfer.

Ni-doped PrBaFe1.9Mo0.1O6-δ (PBFMN) cathode was prepared with EDTA-citric acid sol-gel technique. PBFMN consists of a predominant perovskite phase and a minor NiO phase. The composite cathode demonstrates exceptional catalytic activity and stability. The simulations reveal that the perovskite phase enhances oxygen vacancy and facilitates proton transfer, while the NiO phase enhances oxygen adsorption and dissociation. The fuel cell with PBFMN delivers a Pmax of 1230 W cm-2 at 700 °C.

La0.8Sr0.2Co0.7Ni0.3O3-δ (LSCN) cathode was prepared through glycine sol-gel technique and evaluated as a cathode for PCFC. A single cell with LSCN cathode delivers a Pmax of 1620 mW cm-2 at 700 °C. The LSCN cathode also shows a good durability.

La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) is widely used as cathode of SOFCs due to its high mixed ionic-electronic conductivity, but it faces challenges in PCFC due to slow proton transfer and sluggish ORR kinetics. The Pr2Ni0.5Co0.5O4−δ (PNC), consisting of a perovskite phase and a PrO2 phase, was impregnated onto LSCF surface to enhance the ORR activity and proton transfer. The PCFC with PNC-impregnated LSCF cathode delivers a Pmax of 1857 mW cm−2 at 700 °C.

In this thesis, the traditional perovskite materials were modified and optimized to significantly improve the ORR kinetics of cathode in PCFC.