The
development of proton-exchange membrane fuel cell (PEMFC) technology
will give rise to a great evolution toward a more sustainable and
eco-friendly life by powering clean electric vehicles or stations.
However, several vital problems still hinder the commercialization
of PEMFCs. The foremost issue is the high cost compared to the contenders,
deriving from both the high consumption of Pt catalysts and low service
life under practical operations. In this review, deeper investigations
on how to further lower the cost of PEMFCs show the importance of
understanding and engineering the multiphase transport processes in
the membrane electrode assembly (MEA). The definitions, rules, numerical
simulations, and experimental validations of various mass transfer
processes across the MEA are introduced to provide a holistic evaluation
and enable optimization to improve the cell performance and reliability.
In addition, because the sluggish oxygen reduction reaction in the
cathode catalyst layer (CCL) requires most of the Pt catalysts, the
oxygen/water-related multiphase transfer in CCLs is taken as a focus
for detailed analysis. Several successful strategies, such as triple-phase
boundary engineering, graded design, and novel ordered three-dimensional
structure construction, are proven to be promising in greatly reducing
the Pt consumption in the CCL and facilitating the microscopic multiphase
transfer processes of the MEA. With optimized engineering of the electrode
structure and configuration inside the MEA, the mass transfer resistances
can be minimized to give the best operating conditions for electrochemical
reactions to occur in the catalyst layers. Finally, the main challenges
and some perspectives for developing advanced MEAs with lower cost
in high-performance and reliable PEMFCs are provided.