Anode-supported planar solid oxide fuel cells (SOFC) were fabricated by a single step co-firing process. The cells were composed of a Ni + yittria-stabilized zirconia (YSZ) anode, a YSZ electrolyte, an industrial Ca-doped LaMnO3 (LCM) (or lab-made LCM) + YSZ cathode active layer, and an industrial LCM (or lab-made LCM) cathode current collector layer. The fabrication processes involved tape casting of the anode, screen printing of the electrolyte and the cathode, and one step co-firing of the green-state cells at 1300 degrees C for 2 h. The performance of the cells was greatly improved by optimization of these materials and fabrication processes. The electrochemical performance tests of these cells showed that they could provide a stable power density of 0.2-1.0 W/cm(2) with hydrogen as fuel and air as oxidant while operating in the temperature range 700-900 degrees C. The effects of various polarization losses including ohmic polarization, activation polarization, and concentration polarization were studied by impedance spectroscopy measurements and curve-fitting experimentally measured voltage vs current density traces into an appropriate model. Based on these measurements and curve fitting results, the relationships between cell performance and various polarization losses and their dependence on temperature and microstructure, were rationalized.