The performance of a polymer electrolyte membrane fuel cell (PEMFC) closely depends on internal reactant diffusion and liquid water removal. As one of the key components of PEMFCs, bipolar plates (BPs) provide paths for reactant diffusion and product transport. Therefore, to achieve high fuel cell performance, one key issue is designing BPs with a reasonable flow field. This paper provides a comprehensive review of various modifications of the conventional parallel flow field, interdigitated flow field, and serpentine flow field to improve fuel cells’ overall performance. The main focuses for modifications of conventional flow fields are flow field shape, length, aspect ratio, baffle, trap, auxiliary inlet, and channels, as well as channel numbers. These modifications can partly enhance reactant diffusion and product transport while maintaining an acceptable flow pressure drop. This review also covers the detailed structural description of the newly developed flow fields, including the 3D flow field, metal flow field, and bionic flow field. Moreover, the effects of these flow field designs on the internal physical quantity transport and distribution, as well as the fuel cells’ overall performance, are investigated. This review describes state-of-the-art flow field design, identifies the key research gaps, and provides references and guidance for the design of high-performance flow fields for PEMFCs in the future.

The polymer electrolyte membrane water electrolysis (PEMWE) performance is closely related to the Nafion^® ionomer content in catalyst layers (CLs). This study experimentally investigates the impact of anode and cathode Nafion^® ionomer contents on the PEMWE performance at high temperatures. The Nafion^® ionomer content is 5–30 wt% on both anode and cathode sides, while the temperature and operating pressure change from 80°C to 120°C and 0.1 MPa to 0.3 MPa, respectively. Experimental results reveal that elevated temperature and operating pressure can remarkably promote the performance of PEMWE with a reasonable Nafion^® ionomer content and without dehydrating the membrane at 120°C and 0.3 MPa. However, the PEMWE performance deteriorates as the Nafion^® ionomer content is too low. The anode Nafion^® ionomer content has a relatively great impact on ohmic resistance, concentration, and activation overpotential, especially the concentration overpotential. Nevertheless, the cathode Nafion^® ionomer content only affects the ohmic resistance. Finally, under the operating conditions of 120°C and 0.3 MPa, employing a Nafion ionomer content of 10 wt% in the anode–cathode sides minimizes the electrolysis voltage to 2.18 V at 18 A/cm².