A magnesium-solution phase catholyte semi-fuel cell (SFC) is under development at the Naval Undersea Warfare Center (NUWC) as an energetic electrochemical system for low rate, long endurance undersea vehicle applications. This electrochemical system consists of a magnesium anode, a sodium chloride anolyte, a conductive membrane, a catalyzed carbon current collector, and a catholyte of sodium chloride, sulfuric acid and hydrogen peroxide. Bipolar electrode fabrication to minimize cell stack volume, long duration testing, and scale-up of electrodes from 77 to 1000cm2 have been the objectives of this project. Single cell and multi-cell testing at the 77cm2 configuration have been utilized to optimize all testing parameters including start-up conditions, flow rates, temperatures, and electrolyte concentrations while maintaining high voltages and efficiencies. The fabrication and testing of bipolar electrodes and operating parameter optimization for large electrode area cells will be presented. Designs for 1000cm2 electrodes, electrolyte flow patterns and current/voltage distribution across these large area cells will also be discussed.