A review of key components of hydrogen recirculation subsystem for fuel cell vehicles

•Recent advances in key hydrogen recirculation components for fuel cell vehicles are reviewed.•The design challenge of key components and corresponding suggestions are discussed.•The two-phase flow in hydrogen recirculation components needs to be further investigated.•Research on the dynamic response, integration and control of hydrogen recirculation components is necessary. Hydrogen energy and fuel cell technology are critical clean energy roads to pursue carbon neutrality. The proton exchange membrane fuel cell (PEMFC) has a wide range of commercial application prospects due to its simple structure, easy portability, and quick start-up. However, the cost and durability of the PEMFC system are the main barriers to commercial applications of fuel cell vehicles. In this paper, the core hydrogen recirculation components of fuel cell vehicles, including mechanical hydrogen pumps, ejectors, and gas–water separators, are reviewed in order to understand the problems and challenges in the simulation, design, and application of these components. The types and working characteristics of mechanical pumps used in PEMFC systems are summarized. Furthermore, corresponding design suggestions are given based on the analysis of the design challenges of the mechanical hydrogen pump. The research on structural design and optimization of ejectors for adapting wide power ranges of PEMFC systems is analyzed. The design principle and difficulty of the gas–water separator are summarized, and its application in the system is discussed. In final, the integration and control of hydrogen recirculation components controlled cooperatively to ensure the stable pressure and hydrogen supply of the fuel cell under dynamic loads are reviewed.