Abstract
In this paper, the composition, function and structure of the catalyst layer (CL) of a proton exchange membrane fuel cell (PEMFC) are summarized. The hydrogen reduction reaction (HOR) and oxygen reduction reaction (ORR) processes and their mechanisms and the main interfaces of CL (PEM|CL and CL|MPL) are described briefly. The process of mass transfer (hydrogen, oxygen and water), proton and electron transfer in MEA are described in detail, including their influencing factors. The failure mechanism of CL (Pt particles, CL crack, CL flooding, etc.) and the degradation mechanism of the main components in CL are studied. On the basis of the existing problems, a structure optimization strategy for a high-performance CL is proposed. The commonly used preparation processes of CL are introduced. Based on the classical drying theory, the drying process of a wet CL is explained. Finally, the research direction and future challenges of CL are pointed out, hoping to provide a new perspective for the design and selection of CL materials and preparation equipment.
Highlights
At present, the cost and durability of a fuel cell are the key factors that hinder its largescale commercial application [1,2,3], which is closely related to the properties of membrane electrode assembly (MEA)
These results show that water flooding firstly occurred at the catalyst layer (CL) crack site and eventually resulted in proton exchange membrane (PEM) cracks or pinholes, which was confirmed by X-ray computed tomography (CT) results
Dissolution and redeposition of Pt particles [135] (Ostwald ripening): Within the fuel cell environment, Pt nanoparticles tend to dissolve into ionic form at high potential and re-precipitate on the surface of large particles at low potential, resulting in the continuous reduction of small particles and the continuous growth of large particles, or the dissolved Pt ions will diffuse into PEM and be reduced to Pt particles in the presence of hydrogen
Summary
The cost and durability of a fuel cell are the key factors that hinder its largescale commercial application [1,2,3], which is closely related to the properties of membrane electrode assembly (MEA). MEA is the place where electrochemical reaction takes place in the fuel cell, and it is the key component to convert chemical energy into electrical energy During the power generation process of a fuel cell stack, the properties of MEA affect the transportation of reaction gas, protons and electrons; formation of three phase boundary; output of heat; and production of water [5].
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