Fuel cells are among the most promising and flexible power generation systems, which can directly convert chemical energy into electricity with high efficiency and low emissions. However, the industrial use of fuel cells is hindered by the sluggish activity of the electrodes. In this thesis, we will focus on metal and metal oxide thin films and nanoparticles as the catalysts for fuel cells, including solid oxide fuel cells (SOFCs) and alkaline fuel cells.

The main project in this thesis is about the growth of metal nanoparticles from perovskites. We start from developing a novel A-site deficient perovskite material La_0.4Sr_0.4Sc_0.9Ni_0.1O_3-δ as SOFCs anode material. Ni nanoparticles are in situ exsolved after reduction in H₂ and the sample shows a high electrochemical catalytic ac...[ Read more ]

Fuel cells are among the most promising and flexible power generation systems, which can directly convert chemical energy into electricity with high efficiency and low emissions. However, the industrial use of fuel cells is hindered by the sluggish activity of the electrodes. In this thesis, we will focus on metal and metal oxide thin films and nanoparticles as the catalysts for fuel cells, including solid oxide fuel cells (SOFCs) and alkaline fuel cells.

The main project in this thesis is about the growth of metal nanoparticles from perovskites. We start from developing a novel A-site deficient perovskite material La_0.4Sr_0.4Sc_0.9Ni_0.1O_3-δ as SOFCs anode material. Ni nanoparticles are in situ exsolved after reduction in H₂ and the sample shows a high electrochemical catalytic activity. Insights into the exsolution mechanism are also derived for further material design. To further understand the exsolution mechanism, we use a combined computational and experimental study to understand the Ni segregation in SrTiO₃ system. We find out that A-site vacancy and O vacancy promotes the Ni segregation, while A-site substitution of La hinders it. The nanoparticle exsolution is also found to be catalytic active towards room temperature fuel cell. La_0.9Mn_0.9Pt_0.075Ni_0.025O_3-δ with in situ exsolved Pt₃Ni nanoparticles is developed as a catalyst for oxygen reduction reaction in alkaline solution. The catalytic activity improves significantly after exsolution, which is attributed to the synergistic interaction between the perovskite and the nanoparticles.

Besides from the project of exsolution, there are also some materials that show interesting properties. Layered perovskite oxide films with different orientations show different catalytic activities for SOFCs, which are attributed to the anisotropic oxygen vacancy pathway. Meso-porous MnO_x/S doped graphitized carbon hybrid shows high activity for oxygen catalysis, which is synthesized in situ from wasted polyvinyl chloride plastic.