High-entropy alloys (HEAs) have attracted widespread attention as both structural and functional materials owing to their huge multielement composition space and unique high-entropy mixing structure. Recently, emerging HEAs, either in nano or highly porous bulk forms, are developed and utilized for various catalytic and clean energy applications with superior activity and remarkable durability. Being catalysts, HEAs possess some unique advantages, including (1) a multielement composition space for the discovery of new catalysts and fine-tuning of surface adsorption (i.e., activity and selectivity), (2) diverse active sites derived from the random multielement mixing that are especially suitable for multistep catalysis, and (3) a high-entropy stabilized structure that improves the structural durability in harsh catalytic environments. Benefited from these inherent advantages, HEA catalysts have demonstrated superior catalytic performances and are promising for complex carbon (C) and nitrogen (N) cycle reactions featuring multistep reaction pathways and many different intermediates. However, the design, synthesis, characterization, and understanding of HEA catalysts for C- and N-involved reactions are extremely challenging because of both complex high-entropy materials and complex reactions. In this review, we present the recent development of HEA catalysts, particularly on their innovative and extensive syntheses, advanced (in situ) characterizations, and applications in complex C and N looping reactions, aiming to provide a focused view on how to utilize intrinsically complex catalysts for these important and complex reactions. In the end, remaining challenges and future directions are proposed to guide the development and application of HEA catalysts for highly efficient energy storage and chemical conversion toward carbon neutrality. 

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/cey2.228

High‐entropy alloy catalysts: From bulk to nano toward highly efficient carbon and nitrogen catalysis

High‐entropy alloy (HEA) nanoparticles are emerging catalytic materials and are particularly attractive for multi‐step reactions due to their diverse active sites and multielement tunability. However, their design and optimization often involve lengthy efforts due to the vast multielement space and unidentified active sites. Herein, surface decoration of HEA nanoparticles to drastically improve the overall activity, stability, and reduce cost is reported. A two‐step process is employed to first synthesize non‐noble HEA (FeCoNiSn) nanoparticles and then are surface alloyed with Pd (main active site), denoted as NHEA@NHEA‐Pd. As a demonstration in the ethanol oxidation reaction, a high mass activity of 7.34 A mg−1Pd and superior stability (>91.8% retention after 2000 cycles) in NHEA@NHEA‐Pd are achieved, substantially outperforming traditional HEA, binary M@M‐Pd (M = Sn, Fe, Co, Ni), and commercial Pd/C. In situ spectroscopy reveals that NHEA@NHEA‐Pd can catalytically produce and oxidize CO at <0.5 V, which is >200 mV lower than Sn@Sn‐Pd, suggesting enhanced activity in NHEA@NHEA‐Pd owing to Pd's unique high‐entropy coordination environment. This work provides a novel design of HEA catalysts by combining surface decoration (exposing more active sites) and high‐entropy coordination (enhancing intrinsic activity and structural stability) to boost catalysts’ activity and durability.

Surface‐Decorated High‐Entropy Alloy Catalysts with Significantly Boosted Activity and Stability

Metal-Organic frameworks (MOFs) are increasingly being investigated for the synthesis of carbon-supported metal-based ultrafine nanoparticles (UNPs). However, the collapse of the carbon framework and aggregation of metal particles in the pyrolysis process have severely hindered their stability and applications. Here, we report the synchronous nucleation pseudopyrolysis of MOFs to confine Fe/FeOx UNPs in intact porous carbon nanorods (IPCNs), revealed by in situ transmission electron microscopy experiments and ex situ structure analysis. The pseudopyrolysis mechanism enables strong physical and chemical confinement effects between UNPs and carbon by moderate thermal kinetics and abundant oxygen defects. Further, this strong confinement is greatly beneficial for subsequent chemical transformations to obtain different Fe-based UNPs and excellent electrochemical performance. As a proof of concept, the as-prepared FeSe UNPs in IPCNs show superior lithium storage performance with an ultrahigh and stable capacity of 815.1 mAh g-1 at 0.1 A g -1 and 379.7 mAh g-1 at 5 A g-1 for 1000 cycles.

Pseudopyrolysis of Metal-Organic Frameworks: A Synchronous Nucleation Mechanism to Synthesize Ultrafine Metal Compound Nanoparticles.

ABSTRACT Thermally activated ultrafast diffusion, collision and combination of metal atoms comprise the fundamental processes of synthesizing burgeoning subnanometer metal clusters for diverse applications. However, so far, no method has allowed the kinetically controllable synthesis of subnanometer metal clusters without compromising metal loading. Herein, we have developed, for the first time, a graphene-confined ultrafast radiant heating (GCURH) method for the synthesis of high-loading metal cluster catalysts in microseconds, where the impermeable and flexible graphene acts as a diffusion-constrained nanoreactor for high-temperature reactions. Originating from graphene-mediated ultrafast and efficient laser-to-thermal conversion, the GCURH method is capable of providing a record-high heating and cooling rate of ∼109°C/s and a peak temperature above 2000°C, and the diffusion of thermally activated atoms is spatially limited within the confinement of the graphene nanoreactor. As a result, due to the kinetics-dominant and diffusion-constrained condition provided by GCURH, subnanometer Co cluster catalysts with high metal loading up to 27.1 wt% have been synthesized by pyrolyzing a Co-based metal-organic framework (MOF) in microseconds, representing one of the highest size-loading combinations and the quickest rate for MOF pyrolysis in the reported literature. The obtained Co cluster catalyst not only exhibits an extraordinary activity similar to that of most modern multicomponent noble metal counterparts in the electrocatalytic oxygen evolution reaction, but is also highly convenient for catalyst recycling and refining due to its single metal component. Such a novel GCURH technique paves the way for the kinetically regulated, limited diffusion distance of thermally activated atoms, which in turn provides enormous opportunities for the development of sophisticated and environmentally sustainable metal cluster catalysts.

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Graphene-confined ultrafast radiant heating for high-loading subnanometer metal cluster catalysts

Currently, porous metal-organic frameworks (MOFs) have become popular precursors for the construction of new nanomaterials as a result of their large surface area, high porosity, and excellent chemical, mechanical and...

Multidimensional MOF-derived carbon nanomaterials for multifunctional applications

A general strategy for overcoming the trade-off between ultrasmall size and high loading of MOF-derived metal nanoparticles by millisecond pyrolysis

Significance Refractory carbides are emerging as attractive candidates for support materials in heterogeneous catalysis. However, the industrial applications of refractory carbides, especially silicon carbide (SiC), are greatly hampered because of its low surface area and harsh synthetic conditions during available industrial preparation process. Based on Le Chatelier’s principle, we theoretically proposed and experimentally verified that a low-pressure carbothermal reduction strategy was capable of rapid and scalable synthesis of SiC with remarkably high surface area to satisfy the industrial requirement. Furthermore, our strategy is also applicable to the rapid synthesis of refractory metal carbides and even their emerging high-entropy carbides. The rapid synthesis of carbide-based advanced functional materials is beneficial for their performance research and industrial applications.

A general method for rapid synthesis of refractory carbides by low-pressure carbothermal shock reduction

Carbon-supported nanoparticles are indispensable to enabling new energy technologies such as metal-air batteries and catalytic water splitting. However, achieving ultrasmall and high-density nanoparticles (optimal catalysts) faces fundamental challenges of their strong tendency toward coarsening and agglomeration. Herein, we report a general and efficient synthesis of high-density and ultrasmall nanoparticles uniformly dispersed on two-dimensional porous carbon. This is achieved through direct carbothermal shock pyrolysis of metal-ligand precursors in just ~100 ms, the fastest among reported syntheses. Our results show that the in situ metal-ligand coordination (e.g., N → Co2+) and local ordering during millisecond-scale pyrolysis play a crucial role in kinetically dominated fabrication and stabilization of high-density nanoparticles on two-dimensional porous carbon films. The as-obtained samples exhibit excellent activity and stability as bifunctional catalysts in oxygen redox reactions. Considering the huge flexibility in coordinated precursors design, diversified single and multielement nanoparticles (M = Fe, Co, Ni, Cu, Cr, Mn, Ag, etc) were generally fabricated, even in systems well beyond traditional crystalline coordination chemistry. Our method allows for the transient and general synthesis of well-dispersed nanoparticles with great simplicity and versatility for various application schemes. 

/pdf/transient-and-general-synthesis-of-high-density-and-sjziqnr9.pdf

Ye-Chuang Han

Papers

A general strategy for overcoming the trade-off between ultrasmall size and high loading of MOF-derived metal nanoparticles by millisecond pyrolysis

A general method for rapid synthesis of refractory carbides by low-pressure carbothermal shock reduction

Graphene-confined ultrafast radiant heating for high-loading subnanometer metal cluster catalysts

Transient and general synthesis of high-density and ultrasmall nanoparticles on two-dimensional porous carbon via coordinated carbothermal shock

High-temperature shock synthesis of high-entropy-alloy nanoparticles for catalysis