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High-entropy nanoparticles have become a rapidly growing area of research in recent years. Because of their multielemental compositions and unique high-entropy mixing states (i.e., solid-solution) that can lead to tunable activity and enhanced stability, these nanoparticles have received notable attention for catalyst design and exploration. However, this strong potential is also accompanied by grand challenges originating from their vast compositional space and complex atomic structure, which hinder comprehensive exploration and fundamental understanding. Through a multidisciplinary view of synthesis, characterization, catalytic applications, high-throughput screening, and data-driven materials discovery, this review is dedicated to discussing the important progress of high-entropy nanoparticles and unveiling the critical needs for their future development for catalysis, energy, and sustainability applications.

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Platinum group metal-free (PGM-free) materials based on pyrolyzed M–N–C precursors offer a promising approach to replacing rare and expensive platinum group metal-based oxygen reduction reaction (ORR) electrocatalysts in proton exchange fuel cells (PEFCs). A major issue, however, is the stability of these materials in acidic environments and at potentials experienced in situ in PEFC cathodes and rotating disk electrode (RDE) experiments. Density functional theory (DFT)-based approaches have been valuable to understand how atomic scale structures couple to ORR activity. Little has been reported, however, on quantification of active site structure stability. This work proposes a set of DFT-accessible descriptors for M dissolution (demetalation) that directly address this need. Through the application of this approach to a specific Fe–N4 bilayer graphene-hosted active site structure, the roles of the environment (pH and potential), ORR intermediates, and graphene underlayers are explored. Ranges of stability are reported and hypotheses explaining previously reported experimental behavior based on these findings are proposed. In particular, proposed are model implications for experimental trends in stability with respect to alkaline and acidic conditions; experimental trends for dissolution to occur below a given potential; and observed discrepancies in stability for materials in O2-bearing vs O2-purged environments. Based on these findings, suggestions for improving active site resistance to metal dissolution are provided.

Development of effective nonprecious metal and nitrogen codoped carbon catalysts for the oxygen reduction reaction (ORR) requires a fundamental understanding of the mechanisms underlying their catalytic activity. In this study, we employed the first-principles density functional theory calculations to predict some key parameters (such as activation energy for O−O bond breaking and free-energy evolution as a function of electrode potential) of ORR on three FeN 4 -type active sites with different local carbon structures. We find that the FeN 4 site surrounded by eight carbon atoms and at the edge of micropores has the lowest activation energy (about 0.20 eV) for O−O bond breaking among the three FeN 4 -type active sites for promoting a direct four-electron ORR. Consequently, our computational results suggest that introduction of micropores in the nonprecious metal catalysts could enhance their catalytic activity for ORR through facilitating the formation of FeN 4 −C 8 active sites with high specific activity.

Development of platinum group metal (PGM)-free and iron-free catalysts for the kinetically sluggish oxygen reduction reaction (ORR) is crucial for proton-exchange membrane fuel cells. A major challenge is their insufficient performance and durability in the membrane electrode assembly (MEA) under practical hydrogen-air conditions. Herein, we report an effective strategy to synthesize atomically dispersed Mn−N−C catalysts from an environmentally benign aqueous solution, instead of traditional organic solvents. This innovative synthesis method yields an extremely high surface area for accommodating an increased density of MnN 4 active sites, which was verified by using advanced electron microscopy and X-ray absorption spectroscopy. The Mn−N−C catalyst exhibits promising ORR activity along with significantly enhanced stability, achieving a peak power density of 0.39 W cm −2 under 1.0 bar H 2 -air condition in a MEA, outperforming most PGM-free ORR catalysts. The improved performance is likely due to the unique catalyst features, including the curved surface morphology and dominant graphitic carbon structure, thus benefiting mass transport and improving stability. The first-principles calculations further elucidate the enhanced stability, suggesting that MnN 4 sites have a higher resistance to demetallation than the traditional FeN 4 sites during the ORR.

We elucidate the structural evolution of CoN4 sites during thermal activation by developing a zeolitic imidazolate framework (ZIF)‐8‐derived carbon host as an ideal model for Co2+ ion adsorption. Subsequent in situ X‐ray absorption spectroscopy analysis can dynamically track the conversion from inactive Co−OH and Co−O species into active CoN4 sites. The critical transition occurs at 700 °C and becomes optimal at 900 °C, generating the highest intrinsic activity and four‐electron selectivity for the oxygen reduction reaction (ORR). DFT calculations elucidate that the ORR is kinetically favored by the thermal‐induced compressive strain of Co−N bonds in CoN4 active sites formed at 900 °C. Further, we developed a two‐step (i.e., Co ion doping and adsorption) Co‐N‐C catalyst with increased CoN4 site density and optimized porosity for mass transport, and demonstrated its outstanding fuel cell performance and durability.