Disordered solid‐solution high‐entropy alloys have attracted wide research attention as robust electrocatalysts. In comparison, ordered high‐entropy intermetallics have been hardly explored and the effects of the degree of chemical ordering on catalytic activity remain unknown. In this study, a series of multicomponent intermetallic Pt4FeCoCuNi nanoparticles with tunable ordering degrees is fabricated. The transformation mechanism of the multicomponent nanoparticles from disordered structure into ordered structure is revealed at the single‐particle level, and it agrees with macroscopic analysis by selected‐area electron diffraction and X‐ray diffraction. The electrocatalytic performance of Pt4FeCoCuNi nanoparticles correlates well with their crystal structure and electronic structure. It is found that increasing the degree of ordering promotes electrocatalytic performance. The highly ordered Pt4FeCoCuNi achieves the highest mass activities toward both acidic oxygen reduction reaction (ORR) and alkaline hydrogen evolution reaction (HER) which are 18.9‐fold and 5.6‐fold higher than those of commercial Pt/C, respectively. The experiment also shows that this catalyst demonstrates better long‐term stability than both partially ordered and disordered Pt4FeCoCuNi as well as Pt/C when subject to both HER and ORR. This ordering‐dependent structure–property relationship provides insight into the rational design of catalysts and stimulates the exploration of many other multicomponent intermetallic alloys.
Electrocatalytic water splitting has recently surfaced as a promising method by transforming them into hydrogen fuel. [2] The bottleneck in the development of electrochemical water splitting technology is the oxygen evolution reaction (OER), which is the half reaction at the anode. [3] OER has very sluggish kinetics because it is a four proton-electron transfer process. [4] It is also a vital half-reaction for rechargeable metal-air batteries. [5] Therefore, efficient electrocatalysts are required to overcome the high OER overpotential. Currently, both RuO 2 and IrO 2 are regarded as the state-of-theart electrocatalysts for OER. [6][7][8] However, both of them show poor dissolution resistance under high anodic potential. [9,10] Moreover, their high price and scarcity make it vital to develop cost-effective, highly active, and durable electrocatalysts for OER. [11] Nanomaterial electrocatalysts are generally more efficient than their bulk counterparts due to larger specific surface areas and higher mass activities. Therefore, electrocatalysts with smaller size are normally desired for improved electrocatalytic performance. [12] For example, reducing the size of Cu nanoparticles can significantly increase its catalytic activity because of the increased low-coordination sites acting as active sites. [13] Likewise, size-dependent electrocatalytic activity has also been observed for Au nanoparticles. [14] However, it is still challenging Developing low-cost and efficient oxygen evolution electrocatalysts is key to decarbonization. A facile, surfactant-free, and gram-level biomass-assisted fast heating and cooling synthesis method is reported for synthesizing a series of carbon-encapsulated dense and uniform FeNi nanoalloys with a single-phase face-centered-cubic solid-solution crystalline structure and an average particle size of sub-5 nm. This method also enables precise control of both size and composition. Electrochemical measurements show that among Fe x Ni (1−x) nanoalloys, Fe 0.5 Ni 0.5 has the best performance. Density functional theory calculations support the experimental findings and reveal that the optimally positioned d-band center of O-covered Fe 0.5 Ni 0.5 renders a half-filled antibonding state, resulting in moderate binding energies of key reaction intermediates. By increasing the total metal content from 25 to 60 wt%, the 60% Fe 0.5 Ni 0.5 /40% C shows an extraordinarily low overpotential of 219 mV at 10 mA cm −2 with a small Tafel slope of 23.2 mV dec −1 for the oxygen evolution reaction, which are much lower than most other FeNi-based electrocatalysts and even the state-of-the-art RuO 2 . It also shows robust durability in an alkaline environment for at least 50 h. The gram-level fast heating and cooling synthesis method is extendable to a wide range of binary, ternary, quaternary nanoalloys, as well as quinary and denary high-entropy-alloy nanoparticles.
Development of nanoscale multicomponent solid inorganic materials is often hindered by slow solid diffusion kinetics and poor precursor mixing in conventional solid-state synthesis. These shortcomings can be alleviated by combining nanosized precursor mixtures and low temperature reaction, which could reduce crystal growth and accelerate the solid diffusion at the same time. However, high throughput production of nanoparticle mixtures with tunable composition via conventional synthesis is very challenging. In this work, we demonstrate that ∼10 nm homogeneous mixing of sub-10 nm nanoparticles can be achieved via spark nanomixing at room temperature and pressure. Kinetically driven Spark Plasma Discharge nanoparticle generation and ambient processing conditions limit particle coarsening and agglomeration, resulting in sub-10 nm primary particles of as-deposited films. The intimate mixing of these nanosized precursor particles enables intraparticle diffusion and formation of Cu/Ni nanoalloy during subsequent low temperature annealing at 100 °C. We also discovered that cross-particle diffusion is promoted during the low-temperature sulfurization of Cu/Ag which tends to phase-segregate, eventually leading to the growth of sulfide nanocrystals and improved homogeneity. High elemental homogeneity, small diffusion path lengths, and high diffusibility synergically contribute to faster diffusion kinetics of sub-10 nm nanoparticle mixtures. The combination of ∼10 nm homogeneous precursors via spark nanomixing, low-temperature annealing, and a wide range of potentially compatible materials makes our approach a good candidate as a general platform toward accelerated solid state synthesis of nanomaterials.
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