Engineering Structurally Ordered High-Entropy Intermetallic Nanoparticles with High-Activity Facets for Oxygen Reduction in Practical Fuel Cells

High-Entropy Alloy Nanoflower Array Electrodes with Optimizable Reaction Pathways for Low-Voltage Hydrogen Production at Industrial-Grade Current Density

Developing sufficiently effective non-precious metal catalysts for large-current-density hydrogen production is highly significant but challenging, especially in low-voltage hydrogen production systems. Here, we innovatively report high-entropy alloy nanoflower array (HEANFA) electrodes with optimizable reaction pathways for hydrazine oxidation-assisted hydrogen production at industrial-grade current densities. Atomic-resolution structural analyses confirm the single-phase solid-solution structure of HEANFA. The HEANFA electrodes exhibit the top-level electrocatalytic performance for both the alkaline hydrogen evolution reaction (HER) and hydrazine oxidation reaction (HzOR). Furthermore, the hydrazine oxidation-assisted splitting (OHzS) system assembled with HEANFA as both anode and cathode exhibits a record-breaking performance for hydrogen production. It achieves ultralow working voltages of 0.003, 0.081, 0.260, 0.376, and 0.646 V for current densities of 10, 100, 500, 1 000, and 2 000 mA cm-2, respectively, and remarkable stability for 300 h, significantly outperforming those of previously reported OHzS systems and other chemicals-assisted hydrogen production systems. Theoretical calculations reveal that extraordinary performance of HEANFA for OHzS is attributed to its abundant high-activity sites and optimizable reaction pathways in HER and HzOR. In particular, HEANFA enables intelligent migration of key intermediates during HzOR, thereby optimizing the reaction pathways and creating high-activity sites, ultimately endowing the extraordinary performance for OHzS.

A Library of Seed@High-Entropy-Alloy Core-shell Nanocrystals With Controlled Facets for Catalysis

High-entropy-alloy (HEA) nanocrystals hold immense potential for catalysis, offering virtually unlimited alloy combinations through the inclusion of at least five constituent elements in varying ratios. However, general and effective strategies for synthesizing libraries of HEA nanocrystals with controlled surface atomic structures remain scarce. In this study, a transferable strategy for developing a library of facet-controlled seed@HEA nanocrystals through seed-mediated growth is presented. The synthesis of seed@HEA core-shell nanocrystals incorporating up to ten different metallic elements, with control over the number of solid-solution HEA atomic layers is demonstrated. Epitaxial HEA growth on nanocrystal seeds with low-index and high-index facets leads to the formation of seed@HEA catalyst library with composition- and facet-dependent catalytic activities in both electrocatalysis and photocatalysis. In situ synchrotron X-ray absorption spectroscopy and density-functional theory calculations are employed to identify surface active sites of the HEA, rationalizing the high level of catalytic activities achieved. This work enables facet engineering in the multi-elemental chemical space and unveils the critical needs for their future development toward catalysis.

Accelerating Tandem Electroreduction of Nitrate to Ammonia via Multi-Site Synergy in Mesoporous Carbon-Supported High-Entropy Intermetallics

The electrochemical nitrate reduction reaction (NO3 -RR) for ammonia (NH3) synthesis represents a significant technological advancement, yet it involves a cascade of elementary reactions alongside various intermediates. Thus, the development of multi-site catalysts for enhancing NO3 -RR and understanding the associated reaction mechanisms for NH3 synthesis is vital. Herein, a versatile approach is presented to construct platinum based high-entropy intermetallic (HEI) library for NH3 synthesis. The HEI nanoparticles (NPs) are uniformly supported on a 2D nitrogen doped mesoporous carbon (N-mC) framework, featured with adjustable compositions (up to eight elements) and a high degree of atomic order (over 90%). Guided by the density functional theory (DFT) calculations and atomic structural analysis, a quinary Pt0.8Fe0.2Co0.2Ni0.2Cu0.2 HEI NPs based N-mC catalyst is designed, which demonstrates a large ammonia Faradaic efffciency (>97%) and a remarkable recyclability (>20 cycles) under both acidic and basic conditions. The combined in situ experimental analysis and further DFT calculation suggests that the well-defined multi-sites nature of the HEI NPs cooperate for a tandem reduction mechanism, in which the Pt-X (X represents the other four transition elements) bridging sites offer optimal adsorption for key nitrogen-oxygen species while the Pt sites facilitate the generation and adsorption of *H species.

Entropy Engineering of 2D Materials

Entropy, a measure of disorder or uncertainty in the thermodynamics system, has been widely used to confer desirable functions to alloys and ceramics. The incorporation of three or more principal elements into a single sublattice increases the entropy to medium and high levels, imparting these materials a mélange of advanced mechanical and catalytic properties. In particular, when scaling down the dimensionality of crystals from bulk to the 2D space, the interplay between entropy stabilization and quantum confinement offers enticing opportunities for exploring new fundamental science and applications, since the structural ordering, phase stability, and local electronic states of these distorted 2D materials get significantly reshaped. During the last few years, the large family of high-entropy 2D materials is rapidly expanding to host MXenes, hydrotalcites, chalcogenides, metal-organic frameworks (MOFs), and many other uncharted members. Here, the recent advances in this dynamic field are reviewed, elucidating the influence of entropy on the fundamental properties and underlying elementary mechanisms of 2D materials. In particular, their structure-property relationships resulting from theoretical predictions and experimental findings are discussed. Furthermore, an outlook on the key challenges and opportunities of such an emerging field of 2D materials is also provided.

High-entropy alloy nanomaterials for electrocatalysis

High-entropy alloys (HEAs) exhibit a remarkable capacity to modulate geometric and electronic structures for the construction of catalysts with unpredictable and exceptional performance, and have attracted substantial acclaim within the domain of materials science. In this comprehensive review, we present a thorough summary of the synthesis and multiple applications of HEAs in the realm of electrocatalysis. Our review encompasses the diverse synthesis methodologies of HEA nanomaterials and their pivotal roles in amplifying electrocatalytic performance in hydrogen evolution reactions (HERs), oxygen evolution reactions (OERs), oxygen reduction reactions (ORRs), alcohol oxidation reactions (AORs), and CO2 reduction reactions (CO2RRs), and more. Furthermore, we address the intricate challenges and promising avenues that lie ahead in this research area. Reviewing recent breakthroughs, emerging paradigms, and prospects on the horizon, it becomes increasingly evident that HEAs harbor immense potential to reshape the landscape of energy conversion and storage, and emerge as paramount contenders for the development of cutting-edge electrocatalytic materials that hold the key to a sustainable energy future.

L10-PtCo and L12-Pt3Co Intermetallics for Oxygen Reduction Reaction: The Influence of Composition and Structure on Properties

Pt-based intermetallics are regarded as highly efficient electrocatalysts for oxygen reduction reaction (ORR). However, Pt-based intermetallics with different Pt: M atomic ratios have different atomic arrangements and crystal structures, which will change the electronic structure and coordination environment of Pt, thus affecting the electrocatalytic activity. In this work, we prepared L12-Pt3Co and L10-PtCo intermetallic catalysts by modulating the molar ratio of Pt and Co precursors using a thermal annealing method. The mass activity (MA) of L10-PtCo is 0.52 A mg-1 Pt at 0.9 V, which is 1.44 times larger than that of L12-Pt3Co (0.36 A mg-1 Pt). In addition, the MA of L10-PtCo decreases by 17.31 % after 10,000 CV cycles, which is smaller than that of L12-Pt3Co (25.00 % loss in MA), showing excellent structural stability. Theoretical calculations reveal that compared to L12-Pt3Co, L10-PtCo has more electrons transferred to the Pt sites, which further optimizes the electronic structure of Pt and reduces the d-band center, leading to the increase of the electrocatalytic performance. This work provides new insights into the study of Pt-based intermetallics with different Pt: M ratios, which is helpful for the screening and preparation of high-performance Pt-based intermetallics.

Flame Spray Pyrolysis Synthesis of Ultra-Small High-Entropy Alloy-Supported Oxide Nanoparticles for CO2 Hydrogenation Catalysts

The synthesis of high-entropy alloys (HEAs) with ultra-small particle sizes has long been a challenging task. The complex and time-consuming synthesis process hinders their practical application and widespread adoption. This study presents the novel synthesis of TiO2 nanoparticles loaded with a quinary high-entropy alloy through flame spray pyrolysis (FSP) for the first time. The extremely fast heating rate of flame combustion makes the precursor fast pyrolysis gasification, high temperature in the flame field promotes the metal vapor mixing uniformly, and the fast quenching process can reduce the particle aggregation sintering, the ultra-small particle size of HEA firmly attached to the TiO2 surface. The catalysts prepared via this gas-to-particle pathway exhibit excellent performance in CO2 hydrogenation, achieving a conversion rate of 62% at 450 °C, and maintaining their activity for over 220 h without significant particle agglomeration. This finding provides valuable insights for the future design of catalytically active materials with enhanced activity and long-term stability.

Accelerating the Discovery of Efficient High-Entropy Alloy Electrocatalysts: High-Throughput Experimentation and Data-Driven Strategies

High-entropy alloys (HEAs) present both significant potential and challenges for developing efficient electrocatalysts due to their diverse combinations and compositions. Here, we propose a procedural approach that combines high-throughput experimentation with data-driven strategies to accelerate the discovery of efficient HEA electrocatalysts for the hydrogen evolution reaction (HER). This enables the rapid preparation of HEA arrays with various element combinations and composition ratios within a model system. The intrinsic activity of the HEA arrays is swiftly screened using scanning electrochemical cell microscopy (SECCM), providing precise composition-activity data sets for the HEA system. An ensemble machine learning (EML) model is then used to predict the activity database for the composition subspace of the system. Based on these database results, two groups of promising catalysts are recommended and validated through actual electrocatalytic evaluations. This procedural approach, which combines high-throughput experimentation with data-driven strategies, provides a new pathway to accelerate the discovery of efficient HEA electrocatalysts.

Materials Containing Single-, Di-, Tri-, and Multi-Metal Atoms Bonded to C, N, S, P, B, and O Species as Advanced Catalysts for Energy, Sensor, and Biomedical Applications

Modifying the coordination or local environments of single-, di-, tri-, and multi-metal atom (SMA/DMA/TMA/MMA)-based materials is one of the best strategies for increasing the catalytic activities, selectivity, and long-term durability of these materials. Advanced sheet materials supported by metal atom-based materials have become a critical topic in the fields of renewable energy conversion systems, storage devices, sensors, and biomedicine owing to the maximum atom utilization efficiency, precisely located metal centers, specific electron configurations, unique reactivity, and precise chemical tunability. Several sheet materials offer excellent support for metal atom-based materials and are attractive for applications in energy, sensors, and medical research, such as in oxygen reduction, oxygen production, hydrogen generation, fuel production, selective chemical detection, and enzymatic reactions. The strong metal-metal and metal-carbon with metal-heteroatom (i.e., N, S, P, B, and O) bonds stabilize and optimize the electronic structures of the metal atoms due to strong interfacial interactions, yielding excellent catalytic activities. These materials provide excellent models for understanding the fundamental problems with multistep chemical reactions. This review summarizes the substrate structure-activity relationship of metal atom-based materials with different active sites based on experimental and theoretical data. Additionally, the new synthesis procedures, physicochemical characterizations, and energy and biomedical applications are discussed. Finally, the remaining challenges in developing efficient SMA/DMA/TMA/MMA-based materials are presented.

"One-Stone, Two-Birds": Zinc-Rich Metal-Organic Frameworks as Precursors for High-Entropy Zn-Air Battery Electrocatalysts with Hierarchical Pore Structures

The active sites of inexpensive transition metal electrocatalysts are sparse and singular, thus high-entropy alloys composed of non-precious metals have attracted considerable attention due to their multi-component synergistic effects. However, the facile synthesis of high-entropy alloy composites remains a challenge. Herein, we report a "one-stone, two-birds" method utilizing zinc (Zn)-rich metal-organic frameworks as precursors, by virtue of the low boiling point of Zn (907 °C) and its high volatility in alloys, high-entropy alloy carbon nanocomposite with a layered pore structure was ultimately synthesized. The experimental results demonstrate that the volatilization of zinc can prevent metal agglomeration and contribute to the formation of uniformly dispersed high-entropy alloy nanoparticles at slower pyrolysis and cooling rates. Simultaneously, the volatilization of Zn plays a crucial role in creating the hierarchically porous structure. Compared to the zinc-free HEA/NC-1, the HEA/NC-5 derived from the precursor containing 0.8 Zn exhibit massive micropores and mesopores. The resulting nanocomposites represent a synergistic effect between highly dispersed metal catalytic centers and hierarchical adsorption sites, thus achieving excellent electrocatalytic oxygen reduction performance with low catalyst loading compared to commercial Pt/C. This convenient zinc-rich precursor method can be extended to the production of more high-entropy alloys and various application fields.

High-entropy intermetallics: emerging inorganic materials for designing high-performance catalysts

Alloy materials have been used as promising platforms to upgrade catalytic performance that cannot be achieved with conventional monometallic materials. As a result of numerous efforts, the recent progress in the field of alloy catalysis has been remarkable, and a wide range of new advanced alloys have been considered as potential electro/thermal catalysts. Among advanced alloy materials, high-entropy intermetallics are novel materials, and their excellent catalytic performance has recently been reported. High-entropy intermetallics have several advantages over disordered solid-solution high-entropy alloys, that is, greater structural/thermal stability, more facile site isolation, more precise control of electronic structures, tunability, and multifunctionality. A multidimensional compositional space is indeed limitless, but such a compositional space also provides a well-designed surface configuration because of its ordered nature. In this review, we will provide fundamental insights into high-entropy intermetallics, including thermodynamic properties, synthesis requirements, characterization techniques, roles in catalysis, and reaction examples. The comprehensive information provided in this review will highlight the great application potential of high-entropy intermetallics for catalysis, and will accelerate the development of this newly developed field.

Island-in-Sea Structured Pt3Fe Nanoparticles-in-Fe Single Atoms Loaded in Carbon Materials as Superior Electrocatalysts toward Alkaline HER and Acidic ORR

In this work, Pt3Fe nanoparticles (Pt3Fe NPs) with the ordered internal structure and Pt-rich shells surrounded by plenty of Fe single atoms (Fe SAs) as active species (Pt3Fe NP-in-Fe SA) loaded in the carbon materials are successfully fabricated, which are abbreviated as island-in-sea structured (IISS) Pt3Fe NP-in-Fe SA catalysts. Moreover, the synergistic effect of O-bridging between Pt3Fe NPs and Fe SAs, and the ordered internal structured Pt3Fe NPs with Pt-rich shells of an optimal thickness contributes to the achievement of the local acidic environments on the surfaces of Pt3Fe NPs in the alkaline hydrogen evolution reaction (HER) and the enhancement of the desorption rate of *OH intermediate in the acidic oxygen reduction reaction (ORR). In addition, the electronic interactions between Pt3Fe NPs and dispersed Fe SAs cannot only provide efficient electrons transfer, but also prevent the aggregation and dissolution of Pt3Fe NPs. Furthermore, the overpotential and the half wave potential of the as-prepared IISS Pt3Fe NP-in-Fe SA catalysts toward the alkaline HER and toward the acidic ORR are 8 mV at a current density of 10 mA cm-2 and 0.933 V, respectively, which is 29 lower and 86 mV higher than those (37 mV and 0.847 V) of commercial Pt/C catalysts.

A catalyst family of high-entropy alloy atomic layers with square atomic arrangements comprising iron- and platinum-group metals

We report a catalyst family of high-entropy alloy (HEA) atomic layers having three elements from iron-group metals (IGMs) and two elements from platinum-group metals (PGMs). Ten distinct quinary compositions of IGM-PGM-HEA with precisely controlled square atomic arrangements are used to explore their impact on hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR). The PtRuFeCoNi atomic layers perform enhanced catalytic activity and durability toward HER and HOR when benchmarked against the other IGM-PGM-HEA and commercial Pt/C catalysts. Operando synchrotron x-ray absorption spectroscopy and density functional theory simulations confirm the cocktail effect arising from the multielement composition. This effect optimizes hydrogen-adsorption free energy and contributes to the remarkable catalytic activity observed in PtRuFeCoNi. In situ electron microscopy captures the phase transformation of metastable PtRuFeCoNi during the annealing process. They transform from random atomic mixing (25°C), to ordered L10 (300°C) and L12 (400°C) intermetallic, and finally phase-separated states (500°C).

High-entropy alloy electrocatalysts go to (sub-)nanoscale

Alloying has proven power to upgrade metallic electrocatalysts, while the traditional alloys encounter limitation for optimizing electronic structures of surface metallic sites in a continuous manner. High-entropy alloys (HEAs) overcome this limitation by manageably tuning the adsorption/desorption energies of reaction intermediates. Recently, the marriage of nanotechnology and HEAs has made considerable progresses for renewable energy technologies, showing two important trends of size diminishment and multidimensionality. This review is dedicated to summarizing recent advances of HEAs that are rationally designed for energy electrocatalysis. We first explain the advantages of HEAs as electrocatalysts from three aspects: high entropy, nanometer, and multidimension. Then, several structural regulation methods are proposed to promote the electrocatalysis of HEAs, involving the thermodynamically nonequilibrium synthesis, regulating the (sub-)nanosize and anisotropic morphologies, as well as engineering the atomic ordering. The general relationship between the electronic structures and electrocatalytic properties of HEAs is further discussed. Finally, we outline remaining challenges of this field, aiming to inspire more sophisticated HEA-based nanocatalysts.

High Entropy Alloys Enable Durable and Efficient Lithium-Mediated CO2 Redox Reactions

Designing electrocatalysts with high activity and durability for multistep reduction and oxidation reactions is challenging. High-entropy alloys (HEAs) are intriguing due to their tunable geometric and electronic structure through entropy effects. However, understanding the origin of their exceptional performance and identifying active centers is hindered by the diverse microenvironment in HEAs. Herein, NiFeCoCuRu HEAs designed with an average diameter of 2.17 nm, featuring different adsorption capacities for various reactants and intermediates in Li-mediated CO2 redox reactions, are introduced. The electronegativity-dependent nature of NiFeCoCuRu HEAs induces significant charge redistribution, shifting the d-band center closer to Fermi level and forming highly active clusters of Ru, Co, and Ni for Li-based compounds adsorptions. This lowers energy barriers and simultaneously stabilizes *LiCO2 and LiCO3+CO intermediates, enhancing the efficiency of both CO2 reduction and Li2CO3 decomposition over extended periods. This work provides insights into specific active site interactions with intermediates, highlighting the potential of HEAs as promising catalysts for intricate CO2 redox reactions.

Nanostructured High Entropy Alloys as Structural and Functional Materials

Since their introduction in 2004, high entropy alloys (HEAs) have attracted significant attention due to their exceptional mechanical and functional properties. Advances in our understanding of atomic-scale ordering and phase formation in HEAs have facilitated the development of fabrication techniques for synthesizing nanostructured HEAs. These materials hold immense potential for applications in various fields including automobile industries, aerospace engineering, microelectronics, and clean energy, where they serve as either structural or functional materials. In this comprehensive Review, we conduct an in-depth analysis of the mechanical and functional properties of nanostructured HEAs, with a particular emphasis on the roles of different nanostructures in modulating these properties. To begin, we explore the intrinsic and extrinsic factors that influence the formation and stability of nanostructures in HEAs. Subsequently, we delve into an examination of the mechanical and electrocatalytic properties exhibited by bulk or three-dimensional (3D) nanostructured HEAs, as well as nanosized HEAs in the form of zero-dimensional (0D) nanoparticles, one-dimensional (1D) nanowires, or two-dimensional (2D) nanosheets. Finally, we present an outlook on the current research landscape, highlighting the challenges and opportunities associated with nanostructure design and the understanding of structure-property relationships in nanostructured HEAs.

Stabilizing Diluted Active Sites of Ultrasmall High-Entropy Intermetallics for Efficient Formic Acid Electrooxidation

The poisoning of undesired intermediates or impurities greatly hinders the catalytic performances of noble metal-based catalysts. Herein, high-entropy intermetallics i-(PtPdIrRu)2FeCu (HEI) are constructed to inhibit the strongly adsorbed carbon monoxide intermediates (CO*) during the formic acid oxidation reaction. As probed by multiple-scaled structural characterizations, HEI nanoparticles are featured with partially negative Pt oxidation states, diluted Pt/Pd/Ir/Ru atomic sites and ultrasmall average size less than 2 nm. Benefiting from the optimized structures, HEI nanoparticles deliver more than 10 times promotion in intrinsic activity than that of pure Pt, and well-enhanced mass activity/durability than that of ternary i-Pt2FeCu intermetallics counterpart. In situ infrared spectroscopy manifests that both bridge and top CO* are favored on pure Pt but limited on HEI. Further theoretical elaboration indicates that HEI displayed a much weaker binding of CO* on Pt sites and sluggish diffusion of CO* among different sites, in contrast to pure Pt that CO* bound more strongly and was easy to diffuse on larger Pt atomic ensembles. This work verifies that HEIs are promising catalysts via integrating the merits of intermetallics and high-entropy alloys.

Platinum-group-metal quaternary alloys with lattice defects for enhanced oxygen electrocatalysis

We propose a facile coreduction method to synthesize a platinum-group-metal quaternary alloy anchored on nitrogen-doped hollow carbon spheres (PtPdRuIr/HCS) by using [MClx]y--1-butyl-3-methylimidazole (M = Pt, Pd, Ru, and Ir) ionic liquid. Owing to the steric hindrance of the imidazolium cations, Pt-group metal atoms of different sizes can be deposited at approximately the same pace for the growth of an alloy with lattice defects. The lattice-distorted PtPdRuIr/HCS exhibits enhanced activity toward oxygen electroreduction when benchmarked against Pt counterparts.

Constructing Fully-Active and Ultra-Active Sites in High-Entropy Alloy Nanoclusters for Hydrazine Oxidation-Assisted Electrolytic Hydrogen Production

The development of sufficiently high-efficiency systems and effective catalysts for electrocatalytic hydrogen production is of great significance but challenging. Here, high-entropy alloy nanoclusters (HEANCs) with full-active sites and super-active sites are innovatively constructed for hydrazine oxidation-assisted electrolytic hydrogen production. The HEANCs show an average size of only seven atomic layers (1.48 nm). As the catalysts for both hydrogen evolution reaction (HER) and hydrazine oxidation reaction, the HEANC/C exhibits the best-level performance among reported electrocatalysts. Especially, the HEANC/C achieves an ultrahigh mass activity of 12.85 A mg-1 noble metals at -0.07 V and overpotential of only 9.5 mV for 10 mA cm-2 for alkaline HER. Further, with HEANC/C as both anode and cathode catalysts, an overall hydrazine oxidation-assisted splitting (OHzS) electrolyzer shows a record mass activity of 250.2 mA mg-1 catalysts at 0.1 V and only requires working voltages of 0.025 and 0.181 V to reach 10 and 100 mA cm-2 , respectively, outperforming those of overall water-splitting system and other reported chemicals-assisted hydrogen production systems. Active site libraries including 72 sites on HEANC surface are originally constructed by theoretical calculations, revealing that all sites on HEANC surface are effective active sites for OHzS; especially some are super-active sites, endowing the best-level performance of HEANC/C.

3D microprinting of inorganic porous materials by chemical linking-induced solidification of nanocrystals

Three-dimensional (3D) microprinting is considered a next-generation manufacturing process for the production of microscale components; however, the narrow range of suitable materials, which include mainly polymers, is a critical issue that limits the application of this process to functional inorganic materials. Herein, we develop a generalised microscale 3D printing method for the production of purely inorganic nanocrystal-based porous materials. Our process is designed to solidify all-inorganic nanocrystals via immediate dispersibility control and surface linking-induced interconnection in the nonsolvent linker bath and thereby creates multibranched gel networks. The process works with various inorganic materials, including metals, semiconductors, magnets, oxides, and multi-materials, not requiring organic binders or stereolithographic equipment. Filaments with a diameter of sub-10 μm are printed into designed complex 3D microarchitectures, which exhibit full nanocrystal functionality and high specific surface areas as well as hierarchical porous structures. This approach provides the platform technology for designing functional inorganics-based porous materials.

Intermetallic Nanocrystals for Fuel-Cells-Based Electrocatalysis

Electrocatalysis underpins the renewable electrochemical conversions for sustainability, which further replies on metallic nanocrystals as vital electrocatalysts. Intermetallic nanocrystals have been known to show distinct properties compared to their disordered counterparts, and been long explored for functional improvements. Tremendous progresses have been made in the past few years, with notable trend of more precise engineering down to an atomic level and the investigation transferring into more practical membrane electrode assembly (MEA), which motivates this timely review. After addressing the basic thermodynamic and kinetic fundamentals, we discuss classic and latest synthetic strategies that enable not only the formation of intermetallic phase but also the rational control of other catalysis-determinant structural parameters, such as size and morphology. We also demonstrate the emerging intermetallic nanomaterials for potentially further advancement in energy electrocatalysis. Then, we discuss the state-of-the-art characterizations and representative intermetallic electrocatalysts with emphasis on oxygen reduction reaction evaluated in a MEA setup. We summarize this review by laying out existing challenges and offering perspective on future research directions toward practicing intermetallic electrocatalysts for energy conversions.