“…Driven by increasing demands for renewable clean energy and concerns about environmental pollution, enormous efforts have been devoted to exploring new, green, and sustainable energy sources. , Hydrogen is not only the most abundant element in the universe but also the cleanest fuel on the earth, and it possesses a high energy density (120 MJ kg –1 , three times higher than that of gasoline) with only an exhaust product of water. − Currently, H 2 is mainly produced from fossil fuels ( e.g. , natural gas reforming, petroleum fractionation, and coal gasification). − Therefore, fossil fuel-based hydrogen production is nonrenewable, and its byproductsthe greenhouse effect, acidic rain, ozone holes, and airborne fine particulate matterare environmentally hazardous. , Consequently, green H 2 produced using renewable energy (such as wind, tidal, and solar) has been considered a potential alternative to fossil fuels, as it could address both the energy shortage and environmental pollution caused by fossil fuels. , Among various energy-conversion technologies powered by H 2 , such as solid-oxide fuel cells (SOFCs), alkaline-exchange membrane fuel cells (AEMFCs), and proton-exchange membrane fuel cells (PEMFCs), PEMFCs are more promising due to their easy fabrication, low operation temperature, high efficiency, and technology maturity. , PEMFCs can directly convert the chemical energy released in the reaction of H 2 with O 2 into electrical energy via the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR), at the anode and cathode, respectively, and they can be used for transportation, portable, and stationary applications. Platinum (Pt) group metals (PGMs) are state-of-the-art electrocatalysts for HOR and ORR.…”