![]() ![]() Therefore, in the last two decades, research has focused on reducing or even eliminating the amount of Pt in cathodes by developing catalysts based on low usage of platinum group metals (PGMs) and alternative PGM-free catalysts 2. However, a significant amount of Pt is required to achieve high voltage output and sufficient power densities, which accounts for a substantial part of the total cost of the PEMFCs stack 1. Currently, the state-of-the-art (SoA) ORR catalysts in PEMFCs consist of Pt-based nanoparticles (NPs), and have a broad deployment in hydrogen-powered fuel cell electric vehicles (FCEVs). Relative to the HOR, the sluggish kinetics and high over-potential of the ORR is the critical technical bottleneck for the overall performance of PEMFCs. ![]() In principle, PEMFCs can directly convert renewable chemical energy into electrical energy based on two key electrochemical reactions: the hydrogen oxidation reaction (HOR) at the anode and the oxygen reduction (ORR) at the cathode. Moreover, PEMFCs find applications in the fields of transportation, material handling, stationary, and portable power generation. Among them, proton exchange membrane fuel cells (PEMFCs) stand out owing to their unique advantages of zero-emission of greenhouse gases, high theoretical power density, and energy conversion efficiency. Increasing global energy demand and environmental concerns have driven the development of sustainable energy conversion and storage technologies. This review focuses on all these recent developments and it closes with a discussion of future research directions in the field. Furthermore, the development of advanced characterization techniques allows a deeper understanding of the catalyst evolution under different conditions. These include platinum-based alloys with shape-selected nanostructures, platinum-group-metal-free catalysts such as metal-nitrogen-doped carbon materials and modification of the carbon support to control surface properties and ionomer/catalyst interactions. Recent advances in nanotechnologies and material sciences have led to the discoveries of several highly promising families of materials. This is why improved catalyst and support materials as well as catalyst layer design are critically needed. High platinum cathode loadings contribute significantly to costs. Proton exchange membrane fuel cells have been recently developed at an increasing pace as clean energy conversion devices for stationary and transport sector applications. ![]()
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