Development of an advanced composite bipolar plate is proposed for a unitized regenerative fuel cell and electrolyzer system that operates on pure feed streams (H2/O2 and water, respectively). The composite bipolar plate can greatly simplify "closed-loop" unitized fuel cell/electrolyzer power systems, as it eliminates the need for saturators, a second stack and water/gas phase separation. It provides a substantial system improvement over presently used alkaline systems in that it allows for simple high pressure operation with a high differential pressure. Additionally, it allows for dead-ended H2 and O2 feed for the fuel cell, eliminating parasitic pumping losses required for water removal. Phase I will demonstrate composite bipolar plate-based fuel cell and electrolyzers, and quantify the composite bipolar plate transport and mechanical properties required for system design. In Phase II a full unitized composite bipolar plate stack would be designed and built to size according to NASA requirements.