Band Gap Narrowing in a High-Entropy Spinel Oxide Semiconductor for Enhanced Oxygen Evolution Catalysis

Amorphous/Crystalline Heterostructure Nickel-Cobalt Oxides with Rich Oxygen Vacancies for Electrocatalytic Production of Benzoic Acid Coupled with Nitrate Reduction

Selective four-electron mild electrochemical oxidation of benzyl alcohol to high-value-added benzoic acid is regarded as a green alternative to conventional synthesis methods under moderate conditions. Herein, we synthesize oxygen vacancy-rich amorphous/crystalline heterostructure spinel-type oxides NiCo2O4 as a bifunctional electrocatalyst by a pulse voltammetry electrochemical treatment process, which can be utilized for the anode benzyl alcohol oxidation (AOR) and cathode nitrate reduction reaction (NO3RR), respectively. The designed NiCo2O4-x-25/NF delivers only 1.18 V vs RHE at 10 mA cm-2, and Faraday efficiency of benzoic acid of ∼100%. The systematic studies reveal that the amorphous structure of NiCo2O4-x-25/NF generates abundant oxygen vacancies, promoting the rapid generation of active sites and intermediate species adsorption. Meanwhile, the presence of the crystalline structure accelerates electron transfer and maintains structural stability, thereby improving overall performance. Impressively, it exhibits excellent electrocatalytic performance for AOR coupled with NO3RR in an integrated electrolyzer, achieving a current density of 100 mA cm-2 at an applied low cell voltage of 1.38 V and maintaining superior catalytic stability, withstanding continuous electrolysis for 144 h. This work provides a facile synthesis approach for an amorphous/crystalline heterostructure with high electrocatalytic performance, holding great potential for paired electrosynthesis of value-added chemicals.

Chemistry of Materials Underpinning Photoelectrochemical Solar Fuel Production

Since its inception, photoelectrochemistry has sought to power the generation of fuels, particularly hydrogen, using energy from sunlight. Efficient and durable photoelectrodes, however, remain elusive. Here we review the current state of the art, focusing our discussion on advances in photoelectrodes made in the past decade. We open by briefly discussing fundamental photoelectrochemical concepts and implications for photoelectrode function. We next review a broad range of semiconductor photoelectrodes broken down by material class (oxides, nitrides, chalcogenides, and mature photovoltaic semiconductors), identifying intrinsic properties and discussing their influence on performance. We then identify innovative in situ and operando techniques to directly probe the photoelectrode|electrolyte interface, enabling direct assessment of structure-property relationships for catalytic surfaces in active reaction environments. We close by considering more complex photoelectrochemical fuel-forming reactions (carbon dioxide and nitrogen reduction, as well as alternative oxidation reactions), where product selectivity imposes additional criteria on electrochemical driving force and photoelectrode architecture. By contextualizing recent literature within a fundamental framework, we seek to provide direction for continued progress toward achieving efficient and stable fuel-forming photoelectrodes.

In Situ Controllably Self-Assembled CoFe Oxide Nanosheet Arrays As Efficient Catalytic Electrodes for Oxygen Evolution Reaction at Large Current Density

To advance the hydrogen energy economy, developing efficient water-splitting catalysts is crucial. As a potential candidate for industrial applications, the catalytic performance of CoFe2O4 at a large current density needs to be optimized in combination with a variety of strategies. Here, a brand-new In-doped cobalt ferrite/nickel selenide (CoFe1.7In0.3O4/NiSe2) heterojunction with genuine potential as a highly effective electrocatalyst for the OER at a large current density was reported. Density functional theory calculations demonstrate that the performance enhancement is ascribed to heterogeneous atom doping and a self-supported electrode consisting of cobalt ferrite/nickel selenide heterostructures, which reduce the band center of the Fe d orbit and narrow the band gap of cobalt ferrite. The optimized CoFe1.7In0.3O4/NiSe2 catalyst demonstrates remarkably low overpotentials of 335 mV to achieve current densities of 500 mA cm-2 (η500) for the oxygen evolution reaction, while maintaining complete stability over a 100-h chronocurrent measurement at 500 mA cm-2. In addition, the electrode also demonstrates excellent hydrogen evolution reaction performance and superior durability. This strategy can be extended to other spinel oxides to achieve stable oxygen evolution at a large current density.

Boosting Electrocatalytic Activity of Bimetallic CoNi-MOF for OER and HER Through a Synergistic Bimetallic Approach

Due to the decreasing availability, reduced stability, and high cost of noble metal-based catalysts, the search for stable, efficient, and inexpensive electrocatalysts is of significant importance. In this study, three new isostructural Co(II), Ni(II), and CoNi metal-organic frameworks (MOFs) based on bis-coordinating ligand 3-pyridyl acrylic acid are explored as efficient electrocatalysts. The structure of CoNi-MOF was further confirmed by various experimental techniques. The electrocatalytic activities toward the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) revealed that the bimetallic CoNi-MOF demonstrated significantly greater activity towards OER and HER compared to its monometallic counterparts, Co-MOF and Ni-MOF. CoNi-MOF requires 350 mV and 150 mV overpotential to achieve a current density of 10 mA cm-2 for OER and HER, respectively. Moreover, they exhibited excellent stability for 6 hours and 1000 OER cycles, demonstrating its superiority in these reactions. The significant enhancement in the performance of CoNi-MOF is attributed to the bimetallic synergistic effects between the redox-active metal centers Co2+ and Ni2+, which increase the activity of the catalyst's surface, resulting in enhanced current density and reduced overpotential. The hydrogen bond between coordinated water molecules and un-coordinated carboxylate is essential for the electrochemical stability of the materials.

Improving CO Oxidation Catalysis Over High Entropy Spinels by Increasing Disorder

Enhancing the activity and stability of earth-abundant, heterogeneous catalysts remains a key challenge, requiring new materials design strategies to replace platinum-group metals. Herein, it is demonstrated that increasing the configurational disorder of spinel metal oxides (M3O4, where M is a combination of Cr, Mn, Fe, Co, Ni, Cu, and Zn) leads to significant improvements in carbon monoxide (CO) oxidation performance. A substantial 63% decrease in the T10 value (temperature to reach 10% CO oxidation) is observed by systematically increasing the number of first-row transition metals within the spinel oxide. Long-term stability studies reveal that the most disordered 7-metal spinel oxide exhibited superior resistance to catalyst deactivation compared to the 4-metal variant, showing a decrease in activity of only 4.7% versus 12.2% during 14 h of operation. A solventless thermolysis approach is developed to synthesize a series of medium entropy spinel oxide (MESO) and high entropy spinel oxides (HESOs) from discrete, air-stable molecular precursors. Comprehensive crystal structure determination, elemental distribution analysis, and surface characterization are conducted, establishing a clear structure-function relationship between elemental composition, configurational disorder, and catalytic performance. This work highlights how configurational disorder can serve as an effective design principle for developing both active and stable catalysts.

Spectra-based clustering of high-entropy alloy catalysts: improved insight over use of atomic structure

The investigation of material properties based on atomic structure is a commonly used approach. However, in the study of complex systems such as high-entropy alloys, atomic structure not only covers an excessively vast chemical space, but also has an imprecise correspondence to chemical properties. Herein, we present a label-free machine learning (ML) model based on physics-based spectroscopic descriptors to study the catalytic properties of AgAuCuPdPt high-entropy alloy catalysts. Even if the atomic structures of two such alloys are different, these alloys may have similar catalytic properties if their spectral characteristics match closely. One cluster with the strongest CO adsorption exhibited high selectivity for C2+ product generation, indicating that the spectra-based ML model can provide deeper chemical insight than one based on atomic structure. Moreover, such a model can be extended to other systems with consistent results, thus demonstrating its transferability and versatility. This not only underscores the potential of spectral analysis in identifying high-performance alloy catalysts, but facilitates the formation of a new spectra-based modeling approach and research theory in materials science.

Utilization of Stable and Efficient High-Entropy (Ni0.2Zn0.2Mg0.2Cu0.2Co0.2)Al2O4 Catalyst with Polyvalent Transition Metals to Boost Peroxymonosulfate Activation toward Pollutant Degradation

A polyacrylamide gel method has been used to synthesize a variety of polyvalent-transition-metal-doped Ni position of high entropy spinel oxides (Ni0.2Zn0.2Mg0.2Cu0.2Co0.2)Al2O4-800 °C (A2) on the basis of NiAl2O4, and the catalytic activity of A2 is studied under the synergistic action of peroxymonosulfate (PMS) activation and simulated sunlight. The A2 containing polyvalent transition metals (Ni2+, Cu2+, and Co2+) can effectively activate PMS and efficiently degrade levofloxacin (LEV) and tetracycline hydrochloride (TCH) under simulated sunlight irradiation. After 90 min of light exposure, the degradation percentages of LEV (50 mg L-1) and TCH (100 mg L-1) degrade by the A2/PMS/vis system reach 87.0% and 90.2%, respectively. The superoxide radicals, photoinduced holes, and singlet oxides dominate the catalytic process, while hydroxyl radicals and sulfate radicals play only a small role. The adsorption energy and charge density difference between different systems and PMS are calculated by density functional theory, and the activation efficiency of PMS is studied by combining with the change of the length of the O─O bond of the PMS after adsorption. The catalytic mechanism of A2/PMS/vis system is proposed, which provides a new idea and method for the study of high entropy oxides in the field of catalysis.

Advancements in high-entropy materials for electromagnetic wave absorption

Widespread electromagnetic (EM) interference and pollution have become major issues due to the rapid advancement of fifth-generation (5G) wireless communication technology and devices. Recent advances in high-entropy (HE) materials have opened new opportunities for exploring EM wave absorption abilities to address the issues. The lattice distortion effect of structures, the synergistic effect of multi-element components, and multiple dielectric/magnetic loss mechanisms can offer extensive possibilities for optimizing the balance between impedance matching and attenuation ability, resulting in superior EM wave absorption performance. This review gives a comprehensive review on the recent progress of HE materials for EM wave absorption. We begin with the fundamentals of EM wave absorption materials and the superiority of HE absorbers. Discussions of advanced synthetic methods, in-depth characterization techniques, and electronic properties, especially with regard to regulatable electronic structures through band engineering of HE materials are highlighted. This review also covers current research advancements in a wide variety of HE materials for EM wave absorption, including HE alloys, HE ceramics (mainly HE oxides, carbides, and borides), and other novel HE systems. Finally, insights into future directions for the further development of high-performance HE EM wave absorbers are provided.

Oriented catalysis through chaos: high-entropy spinels in heterogeneous reactions

High-entropy spinel (HES) compounds, as a typical class of high-entropy materials (HEMs), represent a novel frontier in the search for next-generation catalysts. Their unique blend of high entropy, compositional diversity, and structural complexity offers unprecedented opportunities to tailor catalyst properties for enhanced performance (i.e., activity, selectivity, and stability) in heterogeneous reactions. However, there is a gap in a critical review of the catalytic applications of HESs, especially focusing on an in-depth discussion of the structure-property-performance relationships. Therefore, this review aims to provide a comprehensive overview of the development of HESs in catalysis, including definition, structural features, synthesis, characterization, and catalytic regimes. The relationships between the unique structure, favorable properties, and improved performance of HES-driven catalysis are highlighted. Finally, an outlook is presented which provides guidance for unveiling the complexities of HESs and advancing the field toward the rational design of efficient energy and environmental materials.

Copper dual-doping strategy of porous carbon nanofibers and nickel fluoride nanorods as bi-functional oxygen electrocatalysis for effective zinc-air batteries

Designing and developing efficient, low-cost bi-functional oxygen electrocatalysts is essential for effective zinc-air batteries. In this study, we propose a copper dual-doping strategy, which involves doping both porous carbon nanofibers (PCNFs) and nickel fluoride nanoparticles with copper alone, successfully preparing copper-doped nickel fluoride (NiF2) nanorods and copper nanoparticles co-modified PCNFs (Cu@NiF2/Cu-PCNFs) as an efficient bi-functional oxygen electrocatalyst. When copper is doped into the PCNFs in the form of metallic nanoparticles, the doped elemental copper can improve the electronic conductivity of composite materials to accelerate electron conduction. Meanwhile, the copper doping for NiF2 can significantly promote the transformation of nickel fluoride nanoparticles into nanorod structures, thus increasing the electrochemical active surface area and enhancing mass diffusion. The Cu-doped NiF2 nanorods also possess an optimized electronic structure, including a more negative d-band center, smaller bandgap width and lower reaction energy barrier. Under the synergistic effect of these advantages, the obtained Cu@NiF2/Cu-PCNFs exhibit outstanding bi-functional catalytic performances, with a low overpotential of 0.68 V and a peak power density of 222 mW cm-2 in zinc-air batteries (ZABs) and stable cycling for 800 h. This work proposes a one-step way based on the dual-doping strategy, providing important guidance for designing and developing efficient catalysts with well-designed architectures for high-performance ZABs.

Research Progress of High-entropy Oxides for Electrocatalytic Oxygen Evolution Reaction

High-entropy oxides (HEOs), similar to high-entropy materials (HEMs), have "four-core effects", i. e., high-entropy effect, delayed diffusion effect, lattice distortion effect and cocktail effect, which have attracted more and more attention in the scientific field of renewable energy technology due to their unique structural characteristics, variable chemical composition and corresponding functional properties. HEOs have become potential candidates for electrocatalytic oxygen evolution reaction (OER), which is a key half reaction for electrolytic CO2, nitrogen reduction, and water electrolysis. However, the precise synthesis of HEOs with a wide range of components and structures is challenging, not to mention their active and stable operation for OER. In this paper, we review the recent advancements in the electrocatalytic oxygen evolution facilitated by HEOs in water electrolysis. We analyze these developments from the perspectives of activity and stability in acid and alkaline conditions, respectively. Furthermore, we summarize the design from the aspect of element composition, structure, morphology, and catalyst-support interactions, along with related reaction mechanism of HEOs. Additionally, we discuss the current challenges faced by HEOs in the field of OER and suggest potential directions for the future development of HEOs beyond water electrolysis application.

Local Proton-Mediated Synthesis of a High-Entropy Borate Library

High-entropy compounds (HECs) provide extensive possibilities for exploring distinctive properties and potential applications. However, most HECs reported so far are synthesized by an arduous high-temperature treatment and special equipment, which is clearly not scalable for practical application. Here a scalable room-temperature solution synthetic strategy is reported for a library of high-entropy borates with arbitrary metal component numbers from 5 to 12 up to 3302 kinds in total and more than a hundred grams per operation within one minute. In conjunction with theoretical and in situ investigations, it is uncovered that the highly local concentration of protons at ethanol/aqueous interface is favorable to the creation of a stable thermodynamic microenvironment and a desirable kinetic miscibility reservoir, thus enabling a formation of single-phase borates. With the FeCoNiMoCu high-entropy borate, it is further shows that it functions as a highly active catalyst for catalytic oxygen evolution reaction. The work opens up opportunities for the scalable synthesis of HECs for energy storage and conversion applications.

Atomic-Level Electric Polarization in Entropy-Driven Perovskites for Boosting Dielectric Response

Dielectric oxides with robust relaxation responses are fundamental for electronic devices utilized in energy absorption, conversion, and storage. However, the structural origins governing the dielectric response remain elusive due to the involvement of atomically complex compositional and structural environments. Herein, configurational entropy is introduced as a regulatory factor to precisely control the structural heterogeneity in representative perovskite dielectric oxides. Through advanced structural and electric field visualization studies, a novel quantitative relationship is established between atomic-level structural disorder-induced electric field polarization and macroscopic dielectric properties. The results indicate that the degree of atomic delocalization in perovskite oxides exhibits a near-parabolic trend with increasing entropy, reaching a maximum in medium-entropy perovskite. Correspondingly, the atomic electric field vectors display significant asymmetrical distribution, thus greatly enhancing angstrom-scale electric field polarization. Then, it is experimentally proven that entropy-driven electric polarization can improve the dielectric relaxation behavior characterized by broader frequency and stronger intensity of electromagnetic energy absorption, with improvements of approximately 160% and 413% compared to structurally homogeneous control. This study unveils the quantitative correlation between angstrom-scale electric field polarization and dielectric response in perovskite oxides, offering a novel perspective for exploring the structure-property relationship in dielectric materials.

High-Entropy Oxides: Pioneering the Future of Multifunctional Materials

The high-entropy concept affords an effective method to design and construct customized materials with desired characteristics for specific applications. Extending this concept to metal oxides, high-entropy oxides (HEOs) can be fabricated, and the synergistic elemental interactions result in the four core effects, i.e., the high-entropy effect, sluggish-diffusion effect, severe-lattice-distortion effect, and cocktail effect. All these effects greatly enhance the functionalities of this vast material family, surpassing conventional low- and medium-entropy metal oxides. For instance, the high phase stability, excellent electrochemical performance, and fast ionic conductivity make HEOs one of the hot next-generation candidate materials for electrochemical energy conversion and storage devices. Significantly, the extraordinary mechanical, electrical, optical, thermal, and magnetic properties of HEOs are very attractive for applications beyond catalysts and batteries, such as electronic devices, optic equipment, and thermal barrier coatings. This review will overview the entropy-stabilized composition and structure of HEOs, followed by a comprehensive introduction to the electrical, optical, thermal, and magnetic properties. Then, several typical applications, i.e., transistor, memristor, artificial synapse, transparent glass, photodetector, light absorber and emitter, thermal barrier coating, and cooling pigment, are synoptically presented to show the broad application prospect of HEOs. Lastly, the intelligence-guided design and high-throughput screening of HEOs are briefly introduced to point out future development trends, which will become powerful tools to realize the customized design and synthesis of HEOs with optimal composition, structure, and performance for specific applications.

A high entropy metallic-high entropy nonmetallic community as a high performance electrocatalyst for the oxygen evolution reaction and oxygen reduction reaction

The multi-element synergism in high-entropy materials (HEMs) provides great opportunities as multi-functional catalysts or for the promotion of tandem reactions. Herein, a strategy that utilizes a high entropy precursor is proposed to realize the formation of a unique high entropy metallic-high entropy non-metallic community (HEM-HENMC). Aminotriazole acts as a "bonding agent" for the high entropy precursor, and not only binds the five metals Cr, Mn, Fe, Co and Ni together, but also introduces nitrogen and carbon in situ. After simultaneous phosphorization and vulcanization and surface oxidation, the unique HEM-HENMC containing five metals (Cr, Mn, Fe, Co and Ni) and five non-metals (C, N, O, P and S) was successfully prepared. The synergistic effect of the various non-metal and metal ions imparts the HEM-HENMC with excellent electrochemical activity. When used as an OER electrocatalyst, the HEM-HENMC exhibits a low overpotential of 211.9 mV (@10 mA cm-2) and has excellent stability for over 25 h, while as an ORR electrocatalyst, a satisfactory initial voltage of 0.977 V, half wave potential of 0.841 V and excellent 25 h electrochemical stability are achieved. This work provides an important research basis for the development of high entropy metallic-high entropy nonmetallic materials.

High-Entropy Boride HfZrTiTaMoB: Promising Materials for Solar Selective Absorption Coatings in Photothermal Applications

High-entropy borides (HEBs), as a category of high-entropy materials, exhibit remarkable thermal stability, a broad compositional range, and finely tuned electronic structures, leading to an excellent functional performance. Despite these advantages, their application in photothermal materials has rarely been reported. Herein, we employ a HEB target with multiple transition-metal elements to develop solar selective absorption coatings (SSACs) with simple and scalable bilayer structures for photothermal applications. The performance of these coatings is enhanced by designing different antireflective layers. The designed SSACs, both stainless steel (SS)/HEB/Al2O3 and SS/HEB/Si3N4, exhibit high absorptivity and low thermal emittance (α/ε = 90.0%/8.6% and 91.6%/8.6% at 82 °C). Thermal stability tests show that the absorbers could withstand annealing at 500 °C for 5 h, while maintaining a good optical performance. Long-term thermal stability tests indicate that the coatings retained good spectral selectivity after annealing at 400 °C for 100 h. Notably, the coatings demonstrate advanced photothermal conversion efficiencies of 88.3% and 89.9%, respectively, at 400 °C under 100 sun. In practical simulated solar irradiation experiments, the absorber achieves temperatures of about 85 °C under 1 sun, surpassing the performance of commercial nonselective absorbing coatings. Additionally, the absorbers maintained a stable photothermal performance through six on-off cycle experiments. In summary, the designed SSACs based on HEBs exhibit excellent optical properties and efficient photothermal conversion at moderate temperatures. This study highlights the significant benefits and potential advancements in solar energy collection offered by HEB-based SSACs.

The effect of particle size on structural and catalysts for oxygen evolution reaction of (CoFeNiMnCr)3O4 prepared by controlled synthesis with polyvinylpyrrolidone (PVP)

In this study, high-entropy spinel oxides (CoNiMnFeCr)3O4 were synthesized using a PVP-assisted sol-gel method, marking the first report of this approach for producing high-entropy oxides. This method provides new insights into morphology customization through precise temperature control during calcination. Samples were calcined at 800, 900, and 1000 °C, and structural, optical, and electrochemical characterizations were performed to evaluate the impact of synthesis conditions on the oxygen evolution reaction (OER) performance. X-ray diffraction (XRD) confirmed the formation of a single-phase spinel structure with face-centered cubic symmetry. UV-Vis spectroscopy revealed a band gap shift associated with calcination temperature, indicating subtle changes in electronic structure that can influence catalytic behavior. The S-HEO 800 sample exhibited the highest catalytic activity, achieving an overpotential of 316 mV at 10 mA cm-2. Electrochemical tests showed excellent short-term durability, with the electrodes maintaining stable performance for 24 h at 10 mA cm-2. Field emission gun scanning electron microscopy (FEGSEM) analysis revealed that particle size increased with calcination temperature, ranging from 96 nm (S-HEO 800) to 475 nm (S-HEO 1000). X-ray photoelectron spectroscopy (XPS) showed a higher concentration of Cr6+, Cr4+, and Ni3+ ions on the surface of S-HEO 800, correlating with its superior OER performance. Additionally, Raman and FT-IR spectra confirmed the formation of the spinel phase and provided insights into metal-oxygen bonding. Electrochemical impedance spectroscopy (EIS) results indicated that S-HEO 800 exhibited the lowest charge transfer resistance (Rct), further supporting its enhanced catalytic behavior. These findings demonstrate the potential of the PVP-assisted sol-gel method to produce customized high-entropy oxides with tunable morphology, making them promising candidates for energy conversion applications, particularly in water electrolysis.

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.

High-Entropy Materials for Prospective Biomedical Applications: Challenges and Opportunities

With their unique structural characteristics, customizable chemical composition, and adjustable functional characteristics, high-entropy materials (HEMs) have triggered a wide range of interdisciplinary research, especially in the biomedical field. In this paper, the basic concept, core properties, and preparation methods of HEMs are first summarized, and then the application and development of HEMs in the field of biomedical are briefly described. Subsequently, based on the diverse and comprehensive properties of HEMs and a few reported cases, the possible application scenarios of HEMs in biological fields such as biosensors, antibacterial materials, therapeutics, bioimaging, and tissue engineering are prospectively predicted and discussed. Finally, their potential advantages and major challenges is summarized, which may provide useful guidance and principles for researchers to develop and optimize novel HEMs.

High-Entropy Materials for Application: Electricity, Magnetism, and Optics

High-entropy materials (HEMs) have recently emerged as a prominent research focus in materials science, gaining considerable attention because of their complex composition and exceptional properties. These materials typically comprise five or more elements mixed approximately in equal atomic ratios. The resultant high-entropy effects, lattice distortions, slow diffusion, and cocktail effects contribute to their unique physical, chemical, and optical properties. This study reviews the electrical, magnetic, and optical properties of HEMs and explores their potential applications. Additionally, it discusses the theoretical calculation methods and preparation techniques for HEMs, thereby offering insights and prospects for their future development.

Atomic Scale Responses of High Entropy Oxides to Redox Environments

The potential of high entropy oxides (HEOs) as high-performance energy storage materials and catalysts has been mainly understood through their bulk structures. However, the importance of their surfaces, which may play an even more critical role, remains largely unknown. In this study, we employed advanced scanning transmission electron microscopy to investigate the atomic-scale structural and chemical responses of CeYLaHfTiZrOx HEOs to high-temperature redox environments. Our observations reveal dynamic elemental and structural reconstructions in the surface of HEOs under different gas environments, contrasting with the high stability of the bulk structure. Notably, the surfaces of HEO particles consistently exhibit abundant oxygen vacancies, regardless of the redox environment. These findings indicate that HEOs offer distinct advantages in facilitating chemical and electrochemical reactions, relying on oxygen vacancies. Our results also suggest that the exceptional performance of HEOs in energy storage applications arises from surface structural and chemical adaptability.

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.

Surface Oxygen Defect Engineering of A2B2O7 Pyrochlore Semiconductors Boosts the Electrocatalytic Reduction of CO2-to-HCOOH

The electrocatalytic conversion of inert CO2 to value-added chemical fuels powered by renewable energy is one of the benchmark approaches to address excessive carbon emissions and achieve carbon-neutral energy restructuring. However, the adsorption/activation of supersymmetric CO2 is facing insurmountable challenges that constrain its industrial-scale applications. Here, this theory-guided study confronts these challenges by leveraging the synergies of bimetallic sites and defect engineering, where pyrochlore-type semiconductor A2B2O7 is employed as research platform and the conversion of CO2-to-HCOOH as the model reaction. Specifically, defect engineering intensified greatly the chemisorption-induced CO2 polarization via the bimetallic coordination, thermodynamically beneficial to the HCOOH production via the *HCO2 intermediate. The optimal V-BSO-430 electrocatalyst with abundant surface oxygen vacancies achieved a superior HCOOH yield of 116.7 mmol h-1 cm-2 at -1.2 VRHE, rivalling the incumbent similar reaction systems. Furthermore, the unique catalytic unit featured with a Bi1-Sn-Bi2 triangular structure, which is reconstructed by defect engineering, and altered the pathway of CO2 adsorption and activation to allow the preferential affinity of the suspended O atom in *HCO2 to H. As a result, V-BSO-430 gave an impressive FEHCOOH of 93% at -1.0 VRHE. This study held promises for inspiring the exploration of bimetallic materials from the massive semiconductor database.

High Entropy Oxides: Mapping the Landscape from Fundamentals to Future Vistas: Focus Review

High-entropy materials (HEMs) are typically crystalline, phase-pure and configurationally disordered materials that contain at least five elements evenly blended into a solid-solution framework. The discovery of high-entropy alloys (HEAs) and high-entropy oxides (HEOs) disrupted traditional notions in materials science, providing avenues for the exploration of new materials, property optimization, and the pursuit of advanced applications. While there has been significant research on HEAs, the creative breakthroughs in HEOs are still being revealed. This focus review aims at developing a structured framework for expressing the concept of HEM, with special emphasis on the crystal structure and functional properties of HEOs. Insights into the recent synthetic advances, that foster prospective outcomes and their current applications in electrocatalysis, and battery, are comprehensively discussed. Further, it sheds light on the existing constraints in HEOs, highlights the adoption of theoretical and experimental tools to tackle challenges, while delineates potential directions for exploration in energy application.

Constructing High-Performance Cobalt-Based Environmental Catalysts from Spent Lithium-Ion Batteries: Unveiling Overlooked Roles of Copper and Aluminum from Current Collectors

Converting spent lithium-ion batteries (LIBs) cathode materials into environmental catalysts has drawn more and more attention. Herein, we fabricated a Co3O4-based catalyst from spent LiCoO2 LIBs (Co3O4-LIBs) and found that the role of Al and Cu from current collectors on its performance is nonnegligible. The density functional theory calculations confirmed that the doping of Al and/or Cu upshifts the d-band center of Co. A Fenton-like reaction based on peroxymonosulfate (PMS) activation was adopted to evaluate its activity. Interestingly, Al doping strengthened chemisorption for PMS (from -2.615 eV to -2.623 eV) and shortened Co-O bond length (from 2.540 Å to 2.344 Å) between them, whereas Cu doping reduced interfacial charge-transfer resistance (from 28.347 kΩ to 6.689 kΩ) excepting for the enhancement of the above characteristics. As expected, the degradation activity toward bisphenol A of Co3O4-LIBs (0.523 min-1) was superior to that of Co3O4 prepared from commercial CoC2O4 (0.287 min-1). Simultaneously, the reasons for improved activity were further verified by comparing activity with catalysts doped Al and/or Cu into Co3O4. This work reveals the role of elements from current collectors on the performance of functional materials from spent LIBs, which is beneficial to the sustainable utilization of spent LIBs.

Two-Dimensional High-Entropy Selenides for Boosting Visible-Light-Driven Photocatalytic Performance

High-entropy materials (HEMs) have garnered extensive attention owing to their diverse and captivating physicochemical properties. Yet, fine-tuning morphological properties of HEMs remains a formidable challenge, constraining their potential applications. To address this, we present a rapid, low-energy consumption diethylenetriamine (DETA)-assisted microwave hydrothermal method for synthesizing a series of two-dimensional high-entropy selenides (HESes). Subsequently, the obtained HESes are harnessed for photocatalytic water splitting. Noteworthy is the optimized HESes, Cd0.9Zn1.2Mn0.4Cu1.8Cr1.2Se4.5, showcasing an output rate of hydrogen of 16.08 mmol h-1 g-1 and a quantum efficiency of ca. 30% under 420 nm monochromatic LED irradiation. It is revealed that the photocatalytic performance of these HESes stems not only from the enlarged specific surface area and enhanced photogenerated charge carrier utilization efficiency but also from the promoted formation of the Cd-Hads bond, influenced by multiple principal elements on the Cd. These findings provide a guide for the design of HEMs tailored for various applications.

Synthetic Roadmap to a Large Library of Colloidal High-Entropy Rare Earth Oxyhalide Nanoparticles Containing up to Thirteen Metals

Nanoparticles of high-entropy materials that incorporate five or more elements randomized on a crystalline lattice often exhibit synergistic properties that can be influenced by both the identity and number of elements combined. These considerations are especially important for structurally and compositionally complex materials such as multimetal multianion compounds, where cation and anion mixing can influence properties in competitive and contradictory ways. Here, we demonstrate the synthesis of a large library of colloidal high-entropy rare earth oxyhalide (REOX) nanoparticles. We begin with the synthesis of (LaCePrNdSmEuGdDyHoErYbScY)OCl, which homogeneously incorporates 13 distinct rare earth elements. Through time point studies, we find that (LaNdSmGdDy)OCl, a 5-metal analogue, forms through in situ generation of compositionally segregated core@shell@shell intermediates that convert to homogeneously mixed products through apparent core-shell interdiffusion. Assuming that all possible combinations of 5 through 13 rare earth metals are synthetically accessible, we propose the existence of a 7099-member REOCl nanoparticle library, of which we synthesize and characterize 40 distinct members. We experimentally validate the incorporation of a large number of rare earth elements using energy dispersive X-ray spectra, despite closely spaced and overlapping X-ray energy lines, using several fingerprint matching strategies to uniquely correlate experimental and simulated spectra. We confirm homogeneous mixing by analyzing elemental distributions in high-entropy nanoparticles versus physical mixtures of their constituent compounds. Finally, we characterize the band gaps of the 5- and 13-metal REOCl nanoparticles and find a significantly narrowed band gap, relative to the constituent REOCl phases, in (LaCePrNdSmEuGdDyHoErYbScY)OCl but not in (LaNdSmGdDy)OCl.

Colloidal Synthesis of Monodisperse High-Entropy Spinel Oxide Nanocrystals

Synthesis of high-entropy oxide (HEO) nanocrystals has focused on increasing the temperature in the entropy term (T(ΔS)) to overcome the enthalpy term. However, these high temperatures lead to large, polydisperse nanocrystals. In this work, we leverage the low solubility product (Ksp) of metal oxides and optimize the Lewis-acid-catalyzed esterification reaction for equal rate production of the cation monomers to synthesize HEO nanocrystals at low temperatures, producing the smallest (<4 nm) and most monodisperse (<15% size dispersity) HEOs to date. We apply these HEO nanocrystals as electrocatalysts, exhibiting promising activity toward the oxygen evolution reaction in alkaline media, with an overpotential of 345 mV at 10 mA/cm2.

Challenges and Strategies for Synthesizing High Performance Micro and Nanoscale High Entropy Oxide Materials

High-entropy oxide micro/nano materials (HEO MNMs) have shown broad application prospects and have become hot materials in recent years. This review comprehensively provides an overview of the latest developments and covers key aspects of HEO MNMs, by discussing design principles, computer-aided structural design, synthesis challenges and strategies, as well as application areas. The analysis of the synthesis process includes the role of high-throughput process in large-scale synthesis of HEOs MNMs, along with the effects of temperature elevation and undercooling on the formation of HEO MNMs. Additionally, the article summarizes the application of high-precision and in situ characterization devices in the field of HEO MNMs, offering robust support for related research. Finally, a brief introduction to the main applications of HEO MNMs is provided, emphasizing their key performances. This review offers valuable guidance for future research on HEO MNMs, outlining critical issues and challenges in the current field.

Ultrathin High-Entropy Fe-Based Spinel Oxide Nanosheets with Metalloid Band Structures for Efficient Nitrate Reduction toward Ammonia

Spinel oxides with tunable chemical compositions have emerged as versatile electrocatalysts, however their performance is greatly limited by small surface area and low electron conductivity. Here, ultrathin high-entropy Fe-based spinel oxides nanosheets are rationally designed (i.e., (Co0.2Ni0.2Zn0.2Mg0.2Cu0.2)Fe2O4; denotes A5Fe2O4) in thickness of ≈4.3 nm with large surface area and highly exposed active sites via a modified sol-gel method. Theoretic and experimental results confirm that the bandgap of A5Fe2O4 nanosheets is significantly smaller than that of ordinary Fe-based spinel oxides, realizing the transformation of binary spinel oxide from semiconductors to metalloids. As a result, such A5Fe2O4 nanosheets manifest excellent performance for the nitrate reduction reaction (NO3 -RR) to ammonia (NH3), with a NH3 yield rate of ≈2.1 mmol h-1 cm-2 at -0.5 V versus Reversible hydrogen electrode, outperforming other spinel-based electrocatalysts. Systematic mechanism investigations reveal that the NO3 -RR is mainly occurred on Fe sites, and introducing high-entropy compositions in tetrahedral sites regulates the adsorption strength of N and O-related intermediates on Fe for boosting the NO3 -RR. The above findings offer a high-entropy platform to regulate the bandgap and enhance the electrocatalytic performance of spinel oxides.

High-Entropy Photothermal Materials

High-entropy (HE) materials, celebrated for their extraordinary chemical and physical properties, have garnered increasing attention for their broad applications across diverse disciplines. The expansive compositional range of these materials allows for nuanced tuning of their properties and innovative structural designs. Recent advances have been centered on their versatile photothermal conversion capabilities, effective across the full solar spectrum (300-2500 nm). The HE effect, coupled with hysteresis diffusion, imparts these materials with desirable thermal and chemical stability. These attributes position HE materials as a revolutionary alternative to traditional photothermal materials, signifying a transformative shift in photothermal technology. This review delivers a comprehensive summary of the current state of knowledge regarding HE photothermal materials, emphasizing the intricate relationship between their compositions, structures, light-absorbing mechanisms, and optical properties. Furthermore, the review outlines the notable advances in HE photothermal materials, emphasizing their contributions to areas, such as solar water evaporation, personal thermal management, solar thermoelectric generation, catalysis, and biomedical applications. The review culminates in presenting a roadmap that outlines prospective directions for future research in this burgeoning field, and also outlines fruitful ways to develop advanced HE photothermal materials and to expand their promising applications.

High-Entropy Engineering of Cubic SiP with Metallic Conductivity for Fast and Durable Li-Ion Batteries

A cost-effective, scalable ball milling process is employed to synthesize the InGeSiP3 compound with a cubic ZnS structure, aiming to address the sluggish reaction kinetics of Si-based anodes for Lithium-ion batteries. Experimental measurements and first-principles calculations confirm that the synthesized InGeSiP3 exhibits significantly higher electronic conductivity, larger Li-ion diffusivity, and greater tolerance to volume change than its parent phases InGe (or Si)P2 or In (or Ge, or Si)P. These improvements stem from its elevated configurational entropy. Multiple characterizations validate that InGeSiP3 undergoes a reversible Li-storage mechanism that involves intercalation, followed by conversion and alloy reactions, resulting in a reversible capacity of 1733 mA h g-1 with an initial Coulombic efficiency of 90%. Moreover, the InGeSiP3-based electrodes exhibit exceptional cycling stability, retaining an 1121 mA h g-1 capacity with a retention rate of ≈87% after 1500 cycles at 2000 mA g-1 and remarkable high-rate capability, achieving 882 mA h g-1 at 10 000 mA g-1. Inspired by the distinctive characteristic of high entropy, the synthesis is extended to high entropy GaCu (or Zn)InGeSiP5, CuZnInGeSiP5, GaCuZnInGeSiP6, InGeSiP2S (or Se), and InGeSiPSSe. This endeavor overcomes the immiscibility of different metals and non-metals, paving the way for the electrochemical energy storage application of high-entropy silicon-phosphides.

An Unexpected Decrease in Vibrational Entropy of Multicomponent Rutile Oxides

High-entropy oxides (HEOs), featuring infinite chemical composition and exceptional physicochemical properties, are attracting much attention. The configurational entropy caused by a component disorder of HEOs is popularly believed to be the main driving force for thermal stability, while the role of vibrational entropy in the thermodynamic landscape has been neglected. In this study, we systematically investigated the vibrational entropy of multicomponent rutile oxides (including Fe0.5Ta0.5O2, Fe0.333Ti0.333Ta0.333O2, Fe0.25Ti0.25Ta0.25Sn0.25O2, and Fe0.21Ti0.21Ta0.21Sn0.21Ge0.16O2) by precise heat capacity measurements. It is found that vibrational entropy gradually decreases with increasing component disorder, beyond what one could expect from an equilibrium thermodynamics perspective. Moreover, all multicomponent rutile oxides exhibit a positive excess vibrational entropy at 298.15 K. Upon examinations of configuration disorder, size mismatch, phase transition, and polyhedral distortions, we demonstrate that the excess vibrational entropy plays a pivotal role in lowering the crystallization temperature of multicomponent rutile oxides. These findings represent the first experimental confirmation of the role of lattice vibrations in the thermodynamic landscape of rutile HEOs. In particular, vibrational entropy could serve as a novel descriptor to guide the predictive design of multicomponent oxide materials.

Low-temperature synthesis of porous high-entropy (CoCrFeMnNi)3O4 spheres and their application to the reverse water-gas shift reaction as catalysts

A high-entropy porous spinel oxide [(Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)3O4] was synthesized via a solvothermal method and calcination. Solvothermal conditions yielding homogeneous precursor composites with five metals were optimized. Low-temperature calcination of the amorphous composites at 500 °C for 60 min yielded porous spheres formed by small primary particles, with crystal structures attributed to single-phase spinels. The homogeneity of the five elements in the spheres was verified via scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy analysis. The high-entropy (Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)3O4 spheres exhibited superior catalytic activity and long-term stability for the reverse water-gas shift reaction at 700 °C for at least 15 h. The importance of the Cr component in stabilizing the spinel structure was demonstrated. Mn, Fe, Co, and Ni served as active sites in the reaction. The advantage of solvothermal synthesis for porous high-entropy materials was discussed.

Controllable Regulation of the Oxygen Redox Process in Lithium-Oxygen Batteries by High-Configuration-Entropy Spinel with an Asymmetric Octahedral Structure

Designing bifunctional electrocatalysts to boost oxygen redox reactions is critical for high-performance lithium-oxygen batteries (LOBs). In this work, high-entropy spinel (Co0.2Mn0.2Ni0.2Fe0.2Cr0.2)3O4 (HEOS) is fabricated by modulating the internal configuration entropy of spinel and studied as the oxygen electrode catalyst in LOBs. Under the high-entropy atomic environment, the Co-O octahedron in spinel undergoes asymmetric deformation, and the reconfiguration of the electron structure around the Co sites leads to the upward shift of the d-orbital centers of the Co sites toward the Fermi level, which is conducive to the strong adsorption of redox intermediate LiO2 on the surface of the HEOS, ultimately forming a layer of a highly dispersed Li2O2 thin film. Thin-film Li2O2 is beneficial for ion diffusion and electron transfer at the electrode-electrolyte interface, which makes the product easy to decompose during the charge process, ultimately accelerating the kinetics of oxygen redox reactions in LOBs. Based on the above advantages, HEOS-based LOBs deliver high discharge/charge capacity (12.61/11.72 mAh cm-2) and excellent cyclability (424 cycles). This work broadens the way for the design of cathode catalysts to improve oxygen redox kinetics in LOBs.

High-Entropy Lithium Niobate Nanocubes for Photocatalytic Water Splitting under Visible Light

The vast compositional space available in high-entropy oxide semiconductors offers unique opportunities for electronic band structure engineering in an unprecedented large room. In this work, with wide band gap semiconductor lithium niobate (LiNbO3) as a model system, we show that the substitutional addition of high-entropy metal cation mixtures within the Nb sublattice can lead to the formation of a single-phase solid solution featuring a substantially narrowed band gap and intense broadband visible light absorption. The resulting high-entropy LiNbO3 [denoted as Li(HE)O3] crystallizes as well-faceted nanocubes; atomic-resolution imaging and elemental mapping via transmission electron microscopy unveil a distinct local chemical complexity and lattice distortion, characteristics of high-entropy stabilized solid solution phases. Because of the presence of high-entropy stabilized Co2+ dopants that serve as active catalytic sites, Li(HE)O3 nanocubes can accomplish the visible light-driven photocatalytic water splitting in an aqueous solution containing methanol as a sacrificial electron donor without the need of any additional co-catalysts.

Strongly-Interacted NiSe2/NiFe2O4 Architectures Built Through Selective Atomic Migration as Catalysts for the Oxygen Evolution Reaction

The interactions between the catalyst and support are widely used in many important catalytic reactions but the construction of strong interaction with definite microenvironments to understand the structure-activity relationship is still challenging. Here, strongly-interacted composites are prepared via selective exsolution of active NiSe2 from the host matrix of NiFe2O4 (S-NiSe2/NiFe2O4) taking advantage of the differences of migration energy, in which the NiSe2 possessed both high dispersion and small size. The characteristics of spatially resolved scanning transmission X-ray microscopy (STXM) coupled with analytical Mössbauer spectra for the surface and bulk electronic structures unveiled that this strongly interacted composite triggered more charge transfers from the NiSe2 to the host of NiFe2O4 while stabilizing the inherent atomic coordination of NiFe2O4. The obtained S-NiSe2/NiFe2O4 exhibits overpotentials of 290 mV at 10 mA cm-2 for oxygen evolution reaction (OER). This strategy is general and can be extended to other supported catalysts, providing a powerful tool for modulating the catalytic performance of strongly-interacted composites.

High-entropy engineering of the crystal and electronic structures in a Dirac material

Dirac and Weyl semimetals are a central topic of contemporary condensed matter physics, and the discovery of new compounds with Dirac/Weyl electronic states is crucial to the advancement of topological materials and quantum technologies. Here we show a widely applicable strategy that uses high configuration entropy to engineer relativistic electronic states. We take the AMnSb2 (A = Ba, Sr, Ca, Eu, and Yb) Dirac material family as an example and demonstrate that mixing of Ba, Sr, Ca, Eu and Yb at the A site generates the compound (Ba0.38Sr0.14Ca0.16Eu0.16Yb0.16)MnSb2 (denoted as A5MnSb2), giving access to a polar structure with a space group that is not present in any of the parent compounds. A5MnSb2 is an entropy-stabilized phase that preserves its linear band dispersion despite considerable lattice disorder. Although both A5MnSb2 and AMnSb2 have quasi-two-dimensional crystal structures, the two-dimensional Dirac states in the pristine AMnSb2 evolve into a highly anisotropic quasi-three-dimensional Dirac state triggered by local structure distortions in the high-entropy phase, which is revealed by Shubnikov-de Haas oscillations measurements.

Mechanochemically Enabled Metastable Niobium Tungsten Oxides

Metastable compounds have greatly expanded the synthesizable compositions of solid-state materials and have attracted enormous amounts of attention in recent years. Especially, mechanochemically enabled metastable materials synthesis has been very successful in realizing cation-disordered materials with highly simple crystal structures, such as rock salts. Application of the same strategy for other structural types, especially for non-close-packed structures, is peculiarly underexplored. Niobium tungsten oxides (NbWOs), a class of materials that have been under the spotlight because of their diverse structural varieties and promising electrochemical and thermoelectric properties, are ideally suited to fill such a knowledge gap. In this work, we develop a new series of metastable NbWOs and realize one with a fully cation-disordered structure. Furthermore, we find that metastable NbWOs transform to a cation-disordered cubic structure when applied as a Li-ion battery anode, highlighting an intriguing non-close-packed-close-packed conversion process, as evidenced in various physicochemical characterizations, in terms of diffraction, electronic, and vibrational structures. Finally, by comparing the cation-disordered NbWO with other trending cation-disordered oxides, we raise a few key structural features for cation disorder and suggest a few possible research opportunities for this field.

Electron Transfer Efficiency-Regulated Electrochemiluminescence for Rapid Crystallinity Analysis in Layered Materials

The electrochemiluminescence (ECL) signal is largely determined by the electron transfer efficiency. Therefore, in the nanomaterial-involved ECL system, the structure-related electron distribution could affect the electron transfer efficiency and further alter the ECL intensity. These features make the design of versatile ECL-based analytical techniques for probing the correlated structure possible. And it is generally accepted that the increased crystallinity of nanomaterials usually leads to a uniform electron distribution, which provides higher conductivity. Therefore, the crystallinity-improved conductivity could facilitate electron transfer, promote the electrochemical activity of support materials, and boost the efficiency of the ECL reaction. In this study, we have demonstrated that the ECL signal of the graphitic carbon nitride reporter was proportional to the crystallinity of layered double hydroxides (LDHs), which meets the supposition well. On the basis of this phenomenon, an ECL-based crystallinity analysis approach has been established using CdAl-LDHs as the model materials. The universality of this proposed technique was further validated by the rapid and accurate crystallinity determination of ZnAl-LDH samples with diverse crystallinities. This work not only contributes an alternative to the X-ray diffraction technique for the rapid screening of crystallinity in layered materials but also opens a new avenue for the design of ECL-based structure analysis techniques toward nanomaterials and even organic materials by involving electron transfer regulation correlation.

Designing Different Heterometallic Organic Frameworks by Heteroatom and Second Metal Doping Strategies for the Electrocatalytic Oxygen Evolution Reaction

Metal-organic frameworks (MOFs) are considered one of the most significant electrocatalysts for the sluggish oxygen evolution reaction (OER). Hence, a series of novel N,S-codoped Ni-based heterometallic organic framework (HMOF) (NiM-bptz-HMOF, M = Co, Zn, and Mn; bptz = 2,5-bis((3-pyridyl)methylthio)thiadiazole) precatalysts are constructed by the heteroatom and second metal doping strategies. The effective combination of the two strategies promotes electronic conductivity and optimizes the electronic structure of the metal. By regulation of the type and proportion of metal ions, the electrochemical performance of the OER can be improved. Among them, the optimized Ni6Zn1-bptz-HMOF precatalyst exhibits the best performance with an overpotential of 268 mV at 10 mA cm-2 and a small Tafel slope of 72.5 mV dec-1. This work presents a novel strategy for the design of modest heteroatom-doped OER catalysts.

Multiscale Synergetic Bandgap/Structure Engineering in Semiconductor Nanofibrous Aerogels for Enhanced Solar Evaporation

Solar-driven interface evaporation has been identified as a sustainable seawater desalination and water purification technology. Nonetheless, the evaporation performance is still restricted by salt deposition and heat loss owing to weak solar spectrum absorption, tortuous channels, and limited plane area of conventional photothermal material. Herein, the semiconductor nanofibrous aerogels with a narrow bandgap, vertically aligned channels, and a conical architecture are constructed by the multiscale synergetic engineering strategy, encompassing bandgap engineering at the atomic scale and structure engineering at the nano-micro scale. As a proof-of-concept demonstration, a Co-doped MoS2 nanofibrous aerogel is synthesized, which exhibits the entire solar absorption, superhydrophilic, and excellent thermal insulation, achieving a net evaporation rate of 1.62 kg m-2 h-1 under 1 sun irradiation, as well as a synergistically efficient dye ion adsorption function. This work opens up new possibilities for the development of solar evaporators for practical applications in clean water production.

Advancing Evidence-Based Data Interpretation in UV-Vis and Fluorescence Analysis for Nanomaterials: An Analytical Chemistry Perspective

UV-vis spectrophotometry and spectrofluorometry are indispensable tools in education, research, and industrial process controls with widespread applications in nanoscience encompassing diverse nanomaterials and fields. Nevertheless, the prevailing spectroscopic interpretations and analyses often exhibit ambiguity and errors, particularly evident in the nanoscience literature. This analytical chemistry Perspective focuses on fostering evidence-based data interpretation in experimental studies of materials' UV-vis absorption, scattering, and fluorescence properties. We begin by outlining common issues observed in UV-vis and fluorescence analysis. Subsequently, we provide a summary of recent advances in commercial UV-vis spectrophotometric and spectrofluorometric instruments, emphasizing their potential to enhance scientific rigor in UV-vis and fluorescence analysis. Furthermore, we propose potential avenues for future developments in spectroscopic instrumentation and measurement strategies, aiming to further augment the utility of optical spectroscopy in nano research for samples where optical complexity surpasses existing tools. Through a targeted focus on the critical issues related to UV-vis and fluorescence properties of nanomaterials, this Perspective can serve as a valuable resource for researchers, educators, and practitioners.

Self-Floating Nanoporous High-Entropy Oxides with Tunable Bandgap for Efficient Solar Seawater Desalination

Nanoporous high-entropy oxide (np-HEO) powders with tunable composition are integrated with a poly(vinylidene fluoride) network to create self-floating solar absorber films for seawater desalination. By progressively increasing the element count, we obtain an optimized 9-component AlNiCoFeCrMoVCuTi-Ox. Density functional theory (DFT) calculations reveal a remarkable reduction in its bandgap, facilitating the light-induced migration of electrons to conduction bands to generate electron-hole pairs, which recombine to produce heat. Simultaneously, the intricate light reflection and refraction pathways, shaped by the nanoporous structure, coupled with the reduced thermal conductivity attributed to the suboptimal crystalline quality of the np-HEO ensure an effective conversion of captured light into thermal energy. Consequently, all these films demonstrate an impressive absorbance rate exceeding 93% across the 250-2500 nm spectral range. Under one sun, the surface temperature of the 9-component film rapidly rises to 110 °C within 90 s with a high pure water evaporation rate of 2.16 kg m-2 h-1.

High Entropy Sulfide Nanoparticles as Lithium Polysulfide Redox Catalysts

The polysulfide shuttle contributes to capacity loss in lithium-sulfur batteries, which limits their practical utilization. Materials that catalyze the complex redox reactions responsible for the polysulfide shuttle are emerging, but foundational knowledge that enables catalyst development remains limited with only a small number of catalysts identified. Here, we employ a rigorous electrochemical approach to show quantitatively that the lithium polysulfide redox reaction is catalyzed by nanoparticles of a high entropy sulfide material, Zn0.30Co0.31Cu0.19In0.13Ga0.06S. When 2% by weight of the high entropy sulfide is added to the lithium sulfur cathode composite, the capacity and Coulombic efficiency of the resulting battery are improved at both moderate (0.2 C) and high (1 C) charge/discharge rates. Surface analysis of the high entropy sulfide nanoparticles using X-ray photoelectron spectroscopy provides important insights into how the material evolves during the cycling process. The Zn0.30Co0.31Cu0.19In0.13Ga0.06S nanoparticle catalyst outperformed the constituent metal sulfides, pointing to the role that the high-entropy "cocktail effect" can play in the development of advanced electrocatalytic materials for improved lithium sulfur battery performance.

General Route to Colloidally Stable, Low-Dispersity Manganese-Based Ternary Spinel Oxide Nanocrystals

While certain ternary spinel oxides have been well-explored with colloidal nanochemistry, notably the ferrite spinel family, ternary manganese (Mn)-based spinel oxides have not been tamed. A key composition is cobalt (Co)-Mn oxide (CMO) spinel, CoxMn3-xO4, that, despite exemplary performance in multiple electrochemical applications, has few reports in the colloidal literature. Of these reports, most show aggregated and polydisperse products. Here, we describe a synthetic method for small, colloidally stable CMO spinel nanocrystals with tunable composition and low dispersity. By reacting 2+ metal-acetylacetonate (M(acac)2) precursors in an amine solvent under an oxidizing environment, we developed a pathway that avoids the highly reducing conditions of typical colloidal synthesis reactions; these reducing conditions typically push the system toward a monoxide impurity phase. Through surface chemistry studies, we identify organic byproducts and their formation mechanism, enabling us to engineer the surface and obtain colloidally stable nanocrystals with low organic loading. We report a CMO/carbon composite with low organic contents that performs the oxygen reduction reaction (ORR) with a half-wave potential (E1/2) of 0.87 V vs RHE in 1.0 M potassium hydroxide at 1600 rpm, rivaling previous reports for the highest activity of this material in ORR electrocatalysis. We extend the general applicability of this procedure to other Mn-based spinel nanocrystals such as Zn-Mn-O, Fe-Mn-O, Ni-Mn-O, and Cu-Mn-O. Finally, we show the scalability of this method by producing inorganic nanocrystals at the gram scale.

High-Entropy Perovskite Thin Film in the Gd-Nd-Sm-La-Y-Co System: Deposition, Structure and Optoelectronic Properties

Multicomponent equimolar perovskite oxides (ME-POs) have recently emerged as a highly promising class of materials with unique synergistic effects, making them well-suited for applications in such areas as photovoltaics and micro- and nanoelectronics. High-entropy perovskite oxide thin film in the (Gd_0.2Nd_0.2La_0.2Sm_0.2Y_0.2)CoO₃ (RECO, where RE = Gd_0.2Nd_0.2La_0.2Sm_0.2Y_0.2, C = Co, and O = O₃) system was synthesized via pulsed laser deposition. The crystalline growth in an amorphous fused quartz substrate and single-phase composition of the synthesized film was confirmed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Surface conductivity and activation energy were determined using a novel technique implementing atomic force microscopy (AFM) in combination with current mapping. The optoelectronic properties of the deposited RECO thin film were characterized using UV/VIS spectroscopy. The energy gap and nature of optical transitions were calculated using the Inverse Logarithmic Derivative (ILD) and four-point resistance method, suggesting direct allowed transitions with altered dispersions. The narrow energy gap of RECO, along with its relatively high absorption properties in the visible spectrum, positions it as a promising candidate for further exploration in the domains of low-energy infrared optics and electrocatalysis.

Synthesis and Magnetic, Optical, and Electrocatalytic Properties of High-Entropy Mixed-Metal Tungsten and Molybdenum Oxides

High-entropy oxides (HEOs) are of interest for their unique physical and chemical properties. Significant lattice distortions, strain, and tolerance for high-vacancy concentrations set HEOs apart from single-metal or mixed-metal oxides. Herein, we synthesized and characterized the structures and compositions, along with the optical, magnetic, and electrocatalytic properties, of two families of high-entropy mixed-metal tungsten and molybdenum oxides, AWO₄ and B₂Mo₃O₈, where A and B are 3d transition metals. The HEOs A⁶WO₄ (A = Mn, Fe, Co, Ni, Cu, and Zn) and B₂⁵Mo₃O₈ (B = Mn, Fe, Co, Ni, and Zn), as well as all accessible single-metal AWO₄ and B₂Mo₃O₈ parent compounds, were synthesized using high-temperature solid-state methods. X-ray photoelectron spectroscopy analysis of the surfaces revealed that the HEOs largely had the metal oxidation states expected from the bulk chemical formulas, but in some cases they were different than in the parent compounds. A⁶WO₄ exhibited antiferromagnetic (AFM) ordering with a Néel temperature of 30 K, which is less than the average of its AFM parent compounds, and had a narrow band gap of 0.24 eV, which is much lower than all of its parent compounds. B₂⁵Mo₃O₈ was paramagnetic, despite the existence of AFM and ferromagnetic ordering in several of its parent compounds and had no observable band gap, which is analogous to its parent compounds. Both A⁶WO₄ and B₂⁵Mo₃O₈ exhibited superior catalytic activity relative to the parent compounds for the oxygen evolution reaction, the oxidation half reaction of overall water splitting, under alkaline conditions, based on the overpotential required to reach the benchmark surface area normalized current density. Consistent with literature predictions of OER durability for ternary tungsten and molybdenum oxides, A⁶WO₄ and B₂⁵Mo₃O₈ also exhibited stable performance without significant dissolution during 10 h stability experiments at a constant current.