Developing highly durable and active catalysts is essential for improving the performance and longevity of proton exchange membrane fuel cells (PEMFCs). In this study, we propose a novel strategy to enhance catalyst dispersion and stability by incorporating pyrrolic nitrogen-rich carbon (pNC) quantum dots into highly crystalline carbon supports. The introduction of pNC generates strong anchoring sites for Pt nanoparticles, facilitating uniform dispersion and minimizing aggregation, which are key factors in enhancing catalytic performance and durability. The synthesized Pt/CVC150 catalyst exhibited excellent oxygen reduction reaction activity, with a half-wave potential of 0.842 V and a limiting current density of 6.3 mA cm− 2. Under accelerated stress test conditions, the catalyst retained 61.4% of its initial peak power density after prolonged cycling, indicating enhanced durability. Furthermore, single cell testing confirmed its improved electrochemical activity and stability of the Pt/CVC150 catalyst in a practical PEMFC operating environment. These findings suggest that the incorporation of heteroatom-doped carbon moieties onto carbon supports represents a promising strategy for the development of nextgeneration PEMFC catalysts with enhanced performance and longevity.

Low-loaded (1–5 wt%) platinum on carbon-based electrocatalysts (l-Pt/C) for the oxygen reduction reaction (ORR) has garnered attention as a promising approach to advancing fuel cell commercialization. Carbon materials, known for their morphological diversity, high specific surface area, ease of doping, cost-effectiveness, and high electrical conductivity, are widely used as supports for l-Pt/C catalysts. This review provides a comprehensive overview of recent progress in carbonbased l-Pt/C catalysts, focusing on three major strategies: modulating pore structure, utilizing the Pt size effect, and introducing novel Pt active sites. Each strategy is detailed, highlighting its principles, characteristics, and limitations with illustrative examples. Finally, we discuss and offer guidance for future research perspectives on highly active l-Pt/C catalysts for ORR.

Ammonia is considered a promising hydrogen carrier due to its high hydrogen density and liquefaction temperature. Considering that the energy efficiency generally decreases as chemical conversion is repeated, it is more efficient to directly use ammonia as a fuel for fuel cells. However, catalysts in direct ammonia fuel cells have the critical issues of sluggish ammonia oxidation reaction (AOR) rate and poisoning of reaction intermediates. In particular, the use of precious metal as cathodic catalysts has been limited due to ammonia crossover and poisoning. In this study, we introduce Fe-based single-atom catalysts with selective activity for the oxygen reduction reaction (ORR) even in the presence of ammonia. As the Fe content increased, the single-atom structure of the catalysts changed into Fe nanoparticles or carbides. Among our Fe–N–C catalysts, FeNC-50 with a Fe loading amount of 0.34 wt% showed the highest ORR performance regardless of the ammonia concentration. In particular, the difference in activity between the catalysts increased as the concentration increased. The FeNC-50 catalyst showed remarkable stability after 1000 cycles. Therefore, we believe that single-atom dispersion is an important factor in the development of stable non-precious catalysts with high activity and inactivity for the ORR and AOR, respectively.

The poor durability issue of polymer electrolyte membrane fuel cells is a major concern in terms of their commercialization. To understand the degradation mechanism of the catalysts, an accelerated durability test (ADT) was conducted according to the protocol established by internationally accredited organizations. However, reversible and irreversible factors contributing to the loss of activity have not yet been practically segregated because of the limitations of a batch-type three-electrode system, leading to the misunderstanding of the deactivation mechanism. In this study, we investigated the effect of a fresh electrolyte on the ADT and recovery process. When the fresh electrolyte was used at every range of the cycle, the chances of incorrect detection of dissolved CO and Pt ions in the electrolyte were very low. When the same electrolyte was used throughout the test, the accumulated Pt ions were deposited on the surface of the Pt nanoparticles or carbon support, affording an increased electrochemical surface area (ECSA) of Pt. Therefore, we believe that periodic replacement by a fresh electrolyte or a continuous-flow electrolyte is essential for the precise determination of the structural and electrochemical changes in Pt/C catalysts.

Metal–organic frameworks (MOFs) are widely used as supports for single-atom catalysts (SACs) owing to their high specific surface area, porosity, and ordered metal–ligand structure. Their activity can be increased by increasing the number of electrochemically accessible active sites via the formation of atomically dispersed metal catalysts (M–Nx) that coordinate with nitrogen atoms on the MOF. Herein, we introduce the relationship between the size of the MOF as a starting material and the catalytic activity for the oxygen reduction reaction in alkaline media. The morphology and features of the MOFs are critically dependent on their size. Remarkably, cage-like MOFs below 33 nm are converted into collapsed structures and are connected between each MOF, even carbon fiber- or tube-like features, after carbonization. SACs derived from medium-sized MOFs exhibit excellent activity and are comparable to commercial Pt/C catalysts owing to their porous structure. Therefore, we believed that controlling the size of MOFs containing active atoms is an effective method of modulating the morphological properties of the support and even the number of active sites that are closely related to the activity.