Effect of anodic current density on the spreading of infiltrated nickel nanoparticles in nickel-yttria stabilized zirconia cermet anodes

Nickel – yttria stabilized zirconia (Ni-YSZ) anodes for solid oxide fuel cells were infiltrated with nickel nanoparticles with the objective of improving its performance by increasing the density of triple phase boundaries (TPBs). However, the nanoparticles deposited on the YSZ grains are not connected to one another, so the additional TPBs are not electrochemically active. It is postulated that at highly humid conditions (>95% H2O) created by high current density, nickel nanoparticles near the anode-electrolyte interface will spread and percolate, becoming electrochemically active. To study this behavior, infiltrated nickel nanoparticles were exposed to low, high and extreme humidity conditions during testing. When exposed to low humidity, no performance improvement or changes to the nanoparticle morphology was observed. At high humidity, the cell showed performance improvement and when cooled they showed nanoparticle coarsening. Exposure to extreme humidity (≈100%) caused performance to degrade back towards that of an un-infiltrated cell and severe nickel nanoparticles coarsening was observed in the cooled cell. This study validates the hypothesis that exposure to controlled high local humidity conditions can lead to the right amount of spreading of the deposited nickel nanoparticles to achieve percolation, thereby activating their TPBs and improving cell performance.