Passive hydrogen recovery schemes using a vacuum ejector in a proton exchange membrane fuel cell system

The present work describes the development of a passive hydrogen-recirculating scheme for the anode of a proton exchange membrane (PEM) fuel cell system. A vacuum ejector is fluidly connected to the stack anode outlet to entrain the unused hydrogen into the main hydrogen supply. A combination of a continuous-flow mode and a pulse-flow mode is employed to cover a wide range of power consumption. The former deals with the normal and high stack power conditions, while the latter is active only at low stack power. Transient results showed that the hydrogen anode stoichiometry has been successfully stabilized in the range of 1.4-1.6 with an entrainment ratio of 40-50% under the constant system load of 1.45 kW. In addition, the reliable operation of the PEM fuel cell system without any failure during the approximate 1-h test indicates the stability and reliability of the present hydrogen recovery scheme.