It is essential to realize an expected low usage of platinum (Pt) in proton exchange membrane fuel cells (PEMFCs) for the large-scale market penetration of PEMFC-powered vehicles. As well as seeking Pt-based catalysts with a high specific activity, improving Pt utilization through structure optimization of the catalyst layer (CL) has been the main route and apparently a more practical way so far to develop high-performance low-Pt PEMFCs. Despite the significant progress achieved in the past 2–3 decades, a visible gap remains between the current Pt demand of automobile PEMFCs and the target value. To further increase Pt utilization, insights from previous studies are necessary. This review analyzes the structural factors that impact the current-generation efficiency of Pt in PEMFC electrodes in great detail, with emphasis particularly put on the mechanistic and molecule-level insights into the structural effects. The contents include the so-called local transport resistance associated with the permeation and diffusion of oxygen molecules in the ionomer film covering the Pt surface, regulation of ionomer aggregation through molecular interactions between ink components, modulation of ionomer distribution through pore size exclusion and surface electrostatic interaction of the carbon support, optimization of the coupling between the reaction and transport processes through graded composition, and the formation of highways of protons, electrons, and gas molecules through component alignment. We provide a critical analysis of the measurement methods and theoretical models assessing the local transport resistance, which is considered as a crucial issue in the current-generation efficiency of Pt in ultralow-Pt CL. Finally, new opportunities toward the further promotion of Pt utilization are proposed. These subjects and discussions should be of great significance in the rational design and precise fabrication of PEMFC electrodes, and may also inspire similar subjects in other electrochemical energy technologies such as water electrolysis, CO₂ reduction, and batteries.

Low cost alternatives to the expensive and scarce Pt to catalyze the oxygen reduction reaction (ORR) in acid media are essential for the proton-exchange-membrane (PEM) fuel cells to become economically viable. Chemically doped nanocarbons are among the most promising candidates in this regard. We report the facile synthesis and superior electrocatalytic activity of an Fe–N doped nanocarbon composite of carbon nanotubes (CNTs) grown on/between graphene sheets. The structure and composition of the composite is characterized by using a variety of techniques including SEM, TEM, N₂ adsorption/desorption isotherms, XPS, XRD, and Mössbauer spectroscopy. It is shown that the in situ growth of CNTs in the presence of graphene sheets not only produces a tubes-on/between-sheets architecture that enhances the dispersion of CNTs and graphene sheets, but also leads to optimized doping and coordination of nitrogen and Fe which favour the ORR. The composite can catalyze the ORR much more efficiently than either of the single materials containing only CNTs or graphene synthesized under similar conditions, and similarly to Pt/C in both alkaline and acid media.