Impedance spectroscopy has been used to optimize the three-phase boundaries of porous electrodes in solid oxide fuel cells. The three-phase boundaries (TPBs) are the sites where the electrode reaction occurs and their nature is determined by the microstructure of the electrode. The three-phase boundary length (TPBL) of the cathode can be optimized by using small powder particles and a high loading of the particles on the electrolyte surface. The TPBL of the Ni/8YSZ anode can be optimized by using small Ni particles and a high 8YSZ/Ni-particle size ratio.