The carbonation cell system is an electrochemical system which concentrates and separates carbon dioxide from an enclosed environment. Areas of application include spacecraft, submarines, and aircraft employing closed-loop oxygen rebreather systems.Concentration and separation of the carbon dioxide are performed in two stages; Stage I is the concentrating stage using an alkaline electrolyte and Stage II, which uses an acid electrolyte, accomplishes separation of oxygen from the carbon dioxide. The effluent oxygen is returned to the enclosed environment and the carbon dioxide supplied to a reduction system or vented overboard.This paper describes the research and development toward the design of a four-man prototype system. Initial feasibility tests are summarized and results from endurance tests in excess of 2000 hours on the individual system stages are discussed. A comparison with other carbon dioxide removal systems is included.