High-entropy Oxide Research Articles

High Entropy Oxide Duplex Yolk-Shell Structure with Isogenic Amorphous/Crystalline Heterophase as a Promising Anode Material for Lithium-Ion Batteries.

Achieving composition and structure regulation on high entropy materials is a big challenge but will give this kind of new materials a huge boost in energy storage. Herein, a novel high entropy oxide ((CrMnFeCoNi)3O4) duplex yolk-shell structure (DYSHEO) with isogenic amorphous/crystalline heterophase are designed and successfully prepared through a simple microthermal solvothermal reaction followed by mesothermal calcination. The microthermal solvothermal reaction results in high entropy precursor with duplex yolk-shell structure, while the mesothermal calcination (annealing temperature at 450°C) realizes the precursor transformation to (CrMnFeCoNi)3O4 (DYSHEO-450) with isogenic amorphous/crystalline heterophase structure. The high entropy effect, the duplex yolk-shell structure, and the isogenic amorphous/crystalline heterophase endow DYSHEO-450 great advantages as lithium-ion battery anode including reducing ion migration obstruction, accommodating volume expansion, and alleviating the stress. Accordingly, DYSHEO-450 exhibits high capacities of 1721 mAh g-1@0.5A g-1, and 1356 mAh g-1@1 A g-1 after 500 cycles with a capacity retention rate of 90.3%. It also shows excellent performances in practical application as anode of a coin-type full cell. This work provides new ideas and directions for the structural regulation of high-entropy materials.

Reaching medium entropy oxides with rocksalt structure based on cluster-plus-glue-atom model: A case study of Co-Ni-Cu-Zn-O system with tunable optoelectrical properties

Mg–Co–Ni–Cu–Zn–O is the firstly reported high entropy oxide (HEO) which has great promise in optoelectrical applications. However, the multicomponent and decreased configurational entropy by extracting one element from (Mg, Co, Ni, Cu, Zn) makes it difficult to synthesize single-phase medium entropy oxides (MEOs) especially when the cations are non-equimolar. In this paper, we synthesized different compositional-type of non-equimolar Co–Ni–Cu–Zn–O MEOs possessing single-phase rocksalt structure guided by the cluster-plus-glue-atom model. Interestingly, Co21Ni43Cu16Zn16O96 and Co17Ni47Cu16Zn16O96 have the lowest single-phase formation temperature (850 °C) when the total cation content is kept unchanged. Further increase or decrease of Co/Ni content (none, little, more) will increase the difficulty of single-phase formation ability and temperature (900–1200 °C). It is suggested the single-phase formation ability of Co–Ni–Cu–Zn–O MEOs is closely related to the Gibbs free energy (ΔG) and average cation-size difference (δ). The linear decrease of Co content and increase of Ni content can monotonously enlarge the energy band gap (Eg) from 1.52 eV to 1.93 eV and increase the electrical impedance with five orders of magnitude (∼103 Ω–∼108 Ω), which may be valuable in the fields of optoelectrical devices.

Activation of Lattice Oxygen in Nitrogen-Doped High-Entropy Oxide Nanosheets for Highly Efficient Oxygen Evolution Reaction

Activation of Lattice Oxygen in Nitrogen-Doped High-Entropy Oxide Nanosheets for Highly Efficient Oxygen Evolution Reaction

Microstructural and mechanical analysis of (Y0.2Yb0.2Lu0.2Eu0.2Er0.2)3Al5O12 high-entropy oxide ceramic fabricated in-situ via laser powder bed fusion

High-entropy ceramics (HECs) have gained attention for their exceptional properties, yet their manufacturing techniques face challenges of long cycles and complex processes. Laser powder bed fusion (LPBF) technology has the potential to address these challenges. In this study, the phase composition, microstructure, crystallography, density, and hardness were investigated at various scanning speeds. The findings reveal that (Y0.2Yb0.2Lu0.2Eu0.2Er0.2)3Al5O12 (RE3Al5O12) were in-situ synthesized via LPBF. Samples deposited at varying scanning speeds exhibited RE3Al5O12 phase with dendritic morphologies, showing notable enrichment of Al, O, and Eu elements at inter-dendritic and grain boundary. The interior of dendrites has been confirmed to be a garnet-structured high-entropy phase, and it is inferred that the segregation may consist of incompletely reacted Al2O3 and an intermediate phase of (Y0.2Yb0.2Lu0.2Eu0.2Er0.2)3AlO3 (REAlO3). Density, pore morphology, and grain size changed with scanning speed, achieving a density of 97.83 % ± 0.55 % at 60 mm/s. Hardness peaked at 15.09 ± 0.68 GPa at 120 mm/s.

Mixed atomic-scale electronic configuration as a strategy to avoid cocatalyst utilization in photocatalysis by high-entropy oxides

To enhance the activity of photocatalysts for hydrogen production and CO2 conversion, noble metal cocatalysts as electron traps and/or acceptors such as platinum or gold are usually utilized. This study hypothesizes that mixing elements with heterogeneous electronic configurations and diverse electronegativities can provide both acceptor and donor sites of electrons to avoid using cocatalysts. This hypothesis was examined in high-entropy oxides (HEOs), which show high flexibility for atomic-scale compositional changes by keeping their single- or dual-phase structure. A new high-entropy oxide was designed and synthesized by mixing elements with an empty d orbital (titanium, zirconium, niobium and tantalum) and a fully occupied d orbital (gallium). The oxide, synthesized by high-pressure torsion followed by calcination, had two phases (88 wt% orthorhombic (Pbcn) and 12 wt% monoclinic (I2/m)) with an overall composition of TiZrNbTaGaO10.5. It exhibited UV and visible light absorbance with a low bandgap of 2.5 eV, low radiative electron-hole recombination and oxygen vacancy generation due to mixed valences of cations. It successfully acted as a photocatalyst for CO and CH4 production from CO2 conversion and hydrogen production from water splitting without cocatalyst addition. These findings confirm that introducing heterogeneous electronic configurations and electronegativities can be considered as a design criterion to avoid the need to use cocatalysts.

Metalloid Phosphorus Induces Tunable Defect Engineering in High Entropy Oxide Toward Advanced Lithium‐Ion Batteries

AbstractThe inferior electrical conductivity and sluggish lithium storage kinetics of conventional high‐entropy oxide (HEO) are critical issues hindering their commercialization. The high electronegativity of metalloids can ameliorate this predicament by altering the electronic configuration of HEO compared to metals. Herein, metalloid phosphorus doping in spinel‐type HEO (PxA1‐x)B2O4 (A/B = Cr, Mn, Fe, Co, Ni) (P‐HEO) is achieved through a facile sol–gel process. The metalloid phosphorus doping facilitates the transfer of electrons from transition metal sites to phosphorus‐doped sites, resulting in the formation of electron‐rich and electron‐deficient local regions on the HEO surface and is conducive to an increase in the total number of active lithium sites in the electrochemical reaction process. Density functional theory calculation reveals Li adsorption energy on the synthesized P‐HEO is only −1.102 eV, demonstrating that the phosphorus doping enables a strong electronic coupling between lithium ions and P‐HEO. Furthermore, metalloid phosphorus doping also leads to oxygen vacancies formation and lattice distortion, which significantly enhances charge transfer efficiency and diffusion kinetics and results in the enhanced lithium storage performance with impressive rate capability and long‐term stability. These findings provide valuable insights for the design of lattice‐engineered HEO as versatile electrodes for future energy storage applications.

Rapid Chemical Synthesis of High-Entropy Oxide Colloids under Ambient Conditions

Rapid Chemical Synthesis of High-Entropy Oxide Colloids under Ambient Conditions

Sustainable photocatalytic hydrogen peroxide production over octonary high-entropy oxide

The direct utilization of solar energy for the artificial photosynthesis of hydrogen peroxide (H2O2) provides a reliable approach for producing this high-value green oxidant. Here we report on the utility of high-entropy oxide (HEO) semiconductor as an all-in-one photocatalyst for visible light-driven H2O2 production directly from H2O and atmospheric O2 without the need of any additional cocatalysts or sacrificial agents. This high-entropy photocatalyst contains eight earth-abundant metal elements (Ti/V/Cr/Nb/Mo/W/Al/Cu) homogeneously arranged within a single rutile phase, and the intrinsic chemical complexity along with the presence of a high density of oxygen vacancies endow high-entropy photocatalyst with distinct broadband light harvesting capability. An efficient H2O2 production rate with an apparent quantum yield of 38.8% at 550 nm can be achieved. The high-entropy photocatalyst can be readily assembled into floating artificial leaves for sustained on-site production of H2O2 from open water resources under natural sunlight irradiation.

Electrochemical investigation of synthesized (Mg0.21Cr0.21Mn0.21Fe0.21Cu0.16)3O4 high entropy oxide for supercapacitor electrode material

Increasing demand for energy is a significant challenge to achieve sustainable development. The advancement of energy storage device depends on the discovery of novel materials for which high entropy materials are promising candidates and have shown extraordinary electrochemical properties. This study reports the synthesis of novel high entropy oxide (HEO), (Mg0.21Cr0.21Mn0.21Fe0.21Cu0.16)3O4, using sol-gel method followed by calcination at high temperatures. Microscopic images show a homogeneous particle size distribution of 250-500 nm. The structural analysis underscores the importance of optimal stoichiometry for the formation of high-performance single-phase spinel-structured HEO. The XRD and electrochemical analysis emphasize the role of multiple elements in phase stabilization and the elements contribution to the electrochemical performance of the HEO. The oxidation and reduction behaviour of HEO with KOH electrolyte is found to be in the desired potential range of 0 V-0.4 V. The material shows the pseudocapacitive nature with an enhanced specific capacitance of 241 Fg⁻1 at 1 Ag⁻1 and retains 86% of its capacitance even after 2000 cycles, indicating excellent electrochemical stability and performance. This work highlights the potential of high entropy oxides as an advanced material for energy storage applications, offering enhanced stability and performance in supercapacitors.

Evaluation of high-entropy (Cr, Mn, Fe, Co, Ni)-oxide nanofibers and nanoparticles as passive fillers for solid composite electrolytes

Solid-state electrolytes (SSEs) could represent the key to solve safety issues of lithium-ion batteries (LIBs). Among them, those obtained by homogenously dispersing inorganic nanofillers into a polymer matrix combine advantages of all SSE typologies. In this work, high-entropy (Cr,Mn,Fe,Co,Ni) oxide (HEO) with different morphology (nanoparticles or nanofibers) are evaluated as passive fillers for the preparation of composite polyethylene oxide (PEO)-based SSEs. By varying their preparation conditions (calcination at 400 or 800°C for 0.5 or 2 h, followed by rapid cooling) different size and crystallization degree of the oxide grains are obtained. The results of the electrochemical testing of the PEO/HEO composites evidence the crucial role of the filler microstructure and morphology. The best results in terms of electrolyte resistance (22.5 Ω), electrochemical stability window (4.7 V), Li+ transference number (0.37) and ionic conductivity (3.0⋅10−4 S cm−1 at 65°C) are obtained by using well crystallized HEO nanofibers with highly defective surface. The suitability of the most promising composite for practical applications is validated by successfully using it in full cell with commercial high-voltage cathode materials.

Porous amorphous high entropy oxide coated dimensionally stable anode for oxygen evolution reaction in acidic media

Porous amorphous high entropy oxide coated dimensionally stable anode for oxygen evolution reaction in acidic media

Lattice distortion effects in high-entropy oxides: Boosting PMS activation for effective and durable pollutant degradation

Advanced Oxidation Processes (AOPs) are highly effective for pollutant removal, but achieving an optimal combination of high reactivity, corrosion resistance, and long-term stability remains challenging. In this study, the synthesis of a distinctive hollow prismatic high-entropy oxide, (Co0.2Ni0.2Mn0.2Cu0.2Zn0.2)3O4, derived from complex coordination polymers are presented. This high-entropy oxide exhibits significant lattice distortion effects compared to conventional (Co1/3Ni1/3Mn1/3)3O4 and Co3O4. These distortions reduce the metal-O bond length, which enhances cyclic stability during peroxymonosulfate (PMS) activation for pollutant degradation. Additionally, the improved interaction between the catalyst and PMS enhances the generation of reactive oxygen species (ROS), leading to superior catalytic degradation activity. Electron paramagnetic resonance (EPR) and other analytical techniques identify ·OH, 1O2, O2−· as the primary active species in the (Co0.2Ni0.2Mn0.2Cu0.2Zn0.2)3O4/PMS system. A degradation mechanism for tetracycline (TC) is also proposed. This study introduces an innovative approach to water treatment by employing high-entropy oxides to activate PMS, demonstrating substantial potential for practical applications.

Novel High-Entropy oxide Achieves high capacity and stability as an anode for Lithium-Ion batteries

High-entropy oxides possess high theoretical capacity, stable chemical structure, making them highly promising as battery electrode materials. The limited successful synthesis of high-entropy oxide systems has hindered their further development. This study synthesized a six-component high-entropy spinel oxide (FeCoMgCrLiZn)3O4 for the first time and evaluated its electrochemical performance as an anode for lithium-ion batteries. The data show that this single-phase oxide exhibits a high reversible capacity (stabilizing at 800 mAh/g after 300 cycles at 200 mA/g), good cycling stability (800 stable cycles at 2000 mA/g without significant capacity decay), and excellent rate performance. This study expands the high-entropy oxide family and provides a potential strategy for developing next-generation energy storage materials.

Efficient photoreforming of plastic waste using a high-entropy oxide catalyst

Simultaneous catalytic hydrogen (H2) production and plastic waste degradation under light, known as photoreforming, is a novel approach to green fuel production and efficient waste management. Here, we use a high-entropy oxide (HEO), a new family of catalysts with five or more principal cations in their structure, for plastic degradation and simultaneous H2 production. The HEO shows higher activity than that of P25 TiO2, a benchmark photocatalyst, for the degradation of polyethylene terephthalate (PET) plastics in water. Several valuable products are produced by photoreforming of PET bottles and microplastics including H2, terephthalate, ethylene glycol and formic acid. The high activity is attributed to the diverse existence of several cations in the HEO lattice, lattice defects, and appropriate charge carrier lifetime. These findings suggest that HEOs possess high potential as new catalysts for concurrent plastic waste conversion and clean H2 production.

Enhancing coke resistance of Ni-based spinel-type oxides by tuning the configurational entropy

The reforming of CH4 and CO2 into syngas is a highly relevant technology for energy conservation and reducing greenhouse gas emissions, attracting widespread attention in the industry. Inspired by this, this work proposes a general criterion for coke-resistant nickel-based catalysts. By leveraging the high-entropy effect and the lattice distortion of the structure, a high-entropy (NiCaMgZnCo)Al10Ox catalyst was synthesized. The high-entropy oxide exhibited good activity and stability during the DRM reaction over 100 h at 800°C and 650°C, producing only a minimal amount of easily removable carbon deposition. O2-TPO, CO2-TPD, CH4-TPSR, CO2-TPSR, DFT and in situ DRIFT were employed to investigate the mechanism of carbon deposition elimination on the surface of the high-entropy catalyst. Then, a high-entropy strategy for designing coke-resistant catalysts was proposed. This strategy may soon inspire the development of catalysts with enhanced stability and anti-coke deposition properties for various catalytic applications.

Aluminum-doped high-entropy oxide pyrochlore for enhanced lithium storage

Aluminum-doped high-entropy oxide pyrochlore for enhanced lithium storage

A three-in-one strategy of high-entropy, single-crystal, and biphasic approaches to design O3-type layered cathodes for sodium-ion batteries

O3-type layered oxides are promising cathodes for sodium-ion batteries (SIBs). However, severe volume changes, irreversible phase transitions, and sluggish Na+ ion transport kinetics lead to structural collapse and severe capacity loss. Herein, a three-in-one strategy “high entropy, single crystal, and biphase” is proposed to design O3-type layered cathodes for SIBs, which achieves enhanced structural stability and Na+ transport kinetics by the combination effect of multimetal high-entropy, the single crystal, and Li substitution. The as-prepared high-entropy oxide (HEO) cathode, Na(Fe1/6Co1/6Ni1/6Mn1/6Ti1/6)Li1/6O2, exhibits a high reversible capacity of 140.3 mAh g−1, robust cycling stability, exceptional rate capability (86 mAh g−1 at rates of 15C), excellent air-stability, and water-resistance ability. In situ X-ray diffraction reveals that the HEO cathode has highly reversible phase transitions and small volume change (ΔV=3.28 %). Ex situ X-ray absorption spectroscopy reveals that reversible Ni2+/Ni4+, Fe3+/Fe3.6+, and Co3+/Co3.6+ redox couples provide charge compensation for the high-entropy cathode at 2.0∼4.2 V. Notably, the full-cell battery based on the high-entropy cathode and hard carbon anode delivers a specific capacity of 134.3 mAh g−1 and an energy density of 390.8 Wh kg−1. This work provides valuable insights into the design of novel high-performance high-entropy cathodes for SIBs, highlighting a promising avenue for advancing rechargeable battery technology.

Synthesis and electrochemical performance of novel high-entropy spinel oxide (FeCoMgCrLi)3O4

High-entropy oxides (HEOs) are attractive options for anode materials in lithium-ion batteries (LIBs) because of their impressive specific capacity and structural stability. The multi-element composition of HEOs endows them with diverse physicochemical properties. However, the role of different elements in the energy storage mechanism remains unclear, and the limited number of successfully synthesized high-entropy oxide systems currently hinders further development. Therefore, developing HEOs with different compositions and studying their electrochemical properties is of great significance. Using the glycine-nitrate solution combustion synthesis (SCS) method, we produced two new High Entropy Oxides (HEOs), namely (FeCoMgCr)3O4 and (FeCoMgCrLi)3O4, and assessed their electrochemical performance as LIBs anode materials. The studies indicate that the inclusion of lithium significantly enhances the lithium storing capabilities of the material system. Specifically, after undergoing two hundred cycles at a current density of 200 mA/g, (FeCoMgCrLi)3O4 exhibited a specific capacity of 658 mAh/g, which was considerably greater than the specific capacity of (FeCoMgCr)3O4, which was 306.9 mAh/g. This work enriches the spinel-type high-entropy oxide systems and proposes a new design strategy for HEOs as LIBs anode materials.

Reducing noble metal content in water electrolysis catalysts: A study on high-entropy oxides

This study presents the development of high-entropy oxide (HEO) catalysts based on Iridium-Ruthenium oxides (IrRuOx) for the oxygen evolution reaction (OER) in proton exchange membrane water electrolyzers (PEMWEs). By incorporating 3d transition metals such as Fe, Co, and Ni, we achieved catalysts with enhanced performance and stability. Using density functional theory (DFT) calculations, we predicted that HEOs possess a more favorable electronic structure for catalytic reactions. The synthesized rutile-type HEO catalyst (RuIrFeCoNi)O2, created via a molten salt oxidation method, exhibited a low overpotential of 261 mV and excellent cycling stability, maintaining a stable voltage of 1.73 V at 1 A cm−2 over 100 hours of electrolysis. This innovative approach not only reduces noble metal content but also leverages multimetallic synergistic effects to optimize the catalytic performance and stability, offering a promising avenue for the industrial application of acidic water electrolysis in PEMWEs.

Enhanced thermal insulation and corrosion resistance in Ni-Fe cermet through incorporation of high-entropy spinel oxides

The influence of high-entropy spinel oxide (HESO) content on the microstructure, electrical conductivity, and high-temperature corrosion resistance of HESO/NiFe cermets were investigated. The results found that the addition of 10–30 wt% HESO enhanced sintering densification and thermal insulation, although it also resulted in reduced electrical conductivity. Isothermal oxidation tests conducted at 900 °C for 10 hours revealed that cermets containing 30–50 wt% HESO exhibited significantly lower weight gains (0.954–1.167 mg cm⁻²) and oxidation rate constants (0.1057–0.1525 mg² cm⁻⁴ h⁻¹). Furthermore, static corrosion tests in AlF₃-KF-Al₂O₃ molten salt demonstrated that HESO effectively mitigated the erosion of the metallic phase by the fluoride molten salt. This study holds significant potential by providing new insights for the design of inert anodes for aluminum electrolysis and exploring the practical applications of high-entropy oxide materials.