The Chevrolet Sequel is a hybrid crossover SUV concept vehicle developed by General Motors and introduced at the 2005 North American International Auto Show. The Sequel is powered by a fuel cell powertrain, which includes an electronic control unit and a fourth-generation version of GM's fuel-cell stack. A fuel-cell is an electrochemical device that combines hydrogen fuel with oxygen from air to produce electricity. The only waste by-product of that conversion is water vapor.