Movable type printing method to synthesize high-entropy single-atom catalysts

Oxygen-Coordinated Cr Single-Atom Catalyst for Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cells

Carbon-supported metal single-atom catalysts (M-SACs) are promising oxygen reduction reaction (ORR) catalysts. Their ORR activity and selectivity are significantly affected by the heteroatoms that coordinate the central metal atoms. Previous reports found that oxygen-coordinated M-SACs promoted a 2e- ORR rather than the 4e- ORR that is more desirable for fuel cells. Herein, we report for the first time that oxygen-coordinated M-SACs are capable of promoting the 4e- ORR in acid media. We prepared a Cr(acac)-NC catalyst with the central Cr atom coordinated by two O atoms. The Cr(acac)-NC catalyst not only exhibits excellent ORR activity and stability in acid media, but also delivers high proton exchange membrane fuel cell (PEMFC) performance comparable to N-coordinated M-SACs. Density functional theory (DFT) calculations reveal that Cr-O2 moieties located on the zigzag edge of the carbon support are the ORR-active sites.

Spin polarization regulation of Fe-N4 by Fe3 atomic clusters for highly active oxygen reduction reaction

The Fe-N4 motif is regarded as a leading non-precious metal catalyst for the oxygen reduction reaction (ORR) with the potential to replace platinum (Pt), yet achieving or surpassing the performance of Pt-based catalysts remains a significant challenge. In this study, we introduce a modification strategy employing homogeneous few-atom Fe3 cluster to regulate the spin polarization of Fe-N4. Experimental research and theoretical calculations show that the incorporation of the Fe3 cluster significantly enhances the adsorption of Fe-N4 motif toward OH ligands, leading to a structural transformation from a square-planar field (Fe-N4) to a square-pyramid field structure (Fe(OH) -N4). This structural transformation reduces the spin polarization of 3dxz, 3dyz, and 3dz2 orbitals of Fe-N4, resulting in a decrease in unpaired electrons within 3d orbitals. As a result, this modulation leads to moderate adsorption/desorption energies of reaction intermediates, thereby facilitating the ORR process. Moreover, the in-situ spectroscopy confirms that the desorption of OH* on Fe3/Fe(OH) -NC motif is more favorable compared to atomic Fe-NC, indicating a lower energy barrier for ORR. Consequently, the Fe3/Fe-NC catalyst demonstrates outstanding ORR performance with a half-wave potential of 0.836 V vs. reversible hydrogen electrode (RHE) in 0.1 mol L-1 HClO4 solution and 0.936 V vs. RHE in 0.1 mol L-1 KOH solution, even surpassing commercial Pt/C catalyst. It also exhibits excellent Zn-air battery efficiency. Our study introduces a novel approach to modulating the electronic structure of single atoms catalysts by leveraging the robust interaction between single atoms and atomic clusters.

High Entropy Oxide-Polyoxometalate Sub-1 nm Hetero-Nanowires as Cathode Catalysts in Li-O2 Batteries

It is desirable for lithium-oxygen batteries (LOBs) to fabricate the cathode catalysts with high catalytic activity and stability. High entropy oxide (HEO) sub-1 nm nanowires (SNWs) with the nearly 100% active site exposure and intrinsic stability are doubtless one of the best candidates. Herein, under a mild solvothermal condition, by incorporating phosphomolybdic acid (PMA) into multimetal oxide reaction system, a series of HEO-PMA SNWs are successfully prepared, where the variety of metal oxides is adjustable from mono component to six components. When these SNWs as the cathode catalysts are applied to LOBs, the capacity and cycling stability of the LOBs are steadily improved with the metal oxide species increasing stepwise, indicating that the entropy modulation effect plays an important role in enhancing battery performance. Additionally, considering the difference in the intrinsic catalytic activity of various metal oxides, the battery performance is further optimized by keeping the number of elements constant in HEO-PMA SNWs and just adjusting one kind of metal oxide. Particularly, BiCuFeCeWPtOx-PMA SNWs based battery delivers a high capacity (11206 mA h g-1) and excellent stability for 213 cycles, making it a promising electrocatalyst candidate for LOBs.

Progress and perspectives of rapid Joule heating for the preparation of highly efficient catalysts

Functional catalytic materials play an important role in environmental, biological, energy, and other fields, wherein unique properties can be endowed through various synthesis strategies. However, conventional catalyst preparation methods suffer from mild conditions, prolonged treatment and low energy transfer efficiency, thus leading to limited inherent characterisation of catalysts (such as surface oxidation and agglomeration). Recently, the rapid Joule heating method, as a novel synthesis method, has attracted widespread attention owing to its controllable kinetic conditions and eco-friendly operation, while the mechanisms, advantages and recent progress of this method have been summarized in few reviews. Herein, we systematically summarize basic fundamentals and parameters of the Joule heating technique as well as recent processes in terms of effective modification strategies based on Joule heating. Meanwhile, perspective suggestions and challenges for Joule heating methods in terms of catalytic materials are put forward. This review provides an understanding for designing advanced catalytic materials.

Soft nanoforest of metal single atoms for free diffusion catalysis

Metal single atoms are of increasing importance in catalytic reactions. However, the mass diffusion is yet substantially limited by the confined surface of the support in comparison to homogeneous catalysis. Here, we demonstrate that cylindrical micellar brushes with highly solvated poly(2-vinylpyridine) coronas can immobilize 33 types of metal single atoms with 8.3 to 40.9 weight % contents on conventional electrodes under ambient conditions. This is favored by the forest-like hierarchically open soft structure of the micellar brushes and the dynamic coordination between the metals and the pyridine groups. It was found that the nanoforests of individual noble metal single atoms can be well solvated in an aqueous electrolyte to comprehensively expose the atomic active sites and the nanoforest of Pt single atoms on nickel foam reveals high electrochemical performance for hydrogen evolution. The micellar brush support also enables the simultaneous anchoring of multiple single atoms on the cathode of an anion-exchange membrane electrolyzer for long-term stable water electrolysis.

Precise Synthesis of Dual-Single-Atom Electrocatalysts through Pre-Coordination-Directed in Situ Confinement for CO2 Reduction

Dual-single-atom catalysts (DSACs) are the next paradigm shift in single-atom catalysts because of the enhanced performance brought about by the synergistic effects between adjacent bimetallic pairs. However, there are few methods for synthesizing DSACs with precise bimetallic structures. Herein, a pre-coordination strategy is proposed to precisely synthesize a library of DSACs. This strategy ensures the selective and effective coordination of two metals via phthalocyanines with specific coordination sites, such as -F- and -OH-. Subsequently, in situ confinement inhibits the migration of metal pairs during high-temperature pyrolysis, and obtains the DSACs with precisely constructed metal pairs. Despite changing synthetic parameters, including transition metal centers, metal pairs, and spatial geometry, the products exhibit similar atomic metal pairs dispersion properties, demonstrating the universality of the strategy. The pre-coordination strategy synthesized DSACs shows significant CO2 reduction reaction performance in both flow-cell and practical rechargeable Zn-CO2 batteries. This work not only provides new insights into the precise synthesis of DSACs, but also offers guidelines for the accelerated discovery of efficient catalysts.

The Role of Long-Range Interactions Between High-Entropy Single-Atoms in Catalyzing Sulfur Conversion Reactions

Sulfur conversion reactions are the foundation of lithium-sulfur batteries but usually possess sluggish kinetics during practical battery operation. Herein, a high-entropy single-atom catalyst (HESAC) is synthesized for this process. In contrast to conventional dual-atom catalysts that form metal-metal bonds, the center metal atoms in HESAC are not bonded but exhibit long-range interactions at a sub-nanometer distance (<9 Å). The synergistic effect between the long-range interactions and entropy changes enables the regulation of d- and π-electron states. This alteration in the electronic structure improves the adsorption and electronic conductivity of intermediate polysulfides, thereby accelerating their conversion kinetics. Consequently, this leads to a significant enhancement in specific capacities by ≈40% at high rates compared to single-atom catalysts. The resulting lithium-sulfur battery with HESAC demonstrates a remarkable areal capacity of 3.4 mAh cm-2 at 10 C. These findings provide valuable insights into the design principle of metal atom catalysts for electrochemical reactions.

Emerging Strategies for the Synthesis of Correlated Single Atom Catalysts

People have been looking for an energy-efficient and sustainable method to produce future chemicals for decades. Heterogeneous single-atom catalysts (SACs) with atomic dispersion of robust, well-characterized active centers are highly desirable. In particular, correlated SACs with cooperative interaction between adjacent single atoms allow the switching of the single-site pathway to the dual or multisite pathway, thus promoting bimolecular or more complex reactions for the synthesis of fine chemicals. Herein, the structural uniqueness of correlated SACs, including the intermetal distance and electronic interaction in homo/heteronuclear metal sites is featured. Recent advances in the production methods of correlated SACs, showcasing the research status and challenges in traditional methods (such as pyrolysis, wet impregnation, and confined synthesis) for building a comprehensive multimetallic SAC library, are summarized. Emerging strategies such as process automation and continuous-flow synthesis are highlighted, minimizing the inconsistency in laboratory batch production and allowing high throughput screening and upscaling toward the next-stage chemical production by correlated SACs.

Operando elucidation of hydrogen production mechanisms on sub-nanometric high-entropy metallenes

Precise morphological control and identification of structure-property relationships pose formidable challenges for high-entropy alloys, severely limiting their rational design and application in multistep and tandem reactions. Herein, we report the synthesis of sub-nanometric high-entropy metallenes with up to eight metallic elements via a one-pot wet-chemical approach. The PdRhMoFeMn high-entropy metallenes exhibit high electrocatalytic hydrogen evolution performances with 6, 23, and 26 mV overpotentials at -10 mA cm-2 in acidic, neutral, and alkaline media, respectively, and high stability. The electrochemical measurements, theoretical simulations, and operando X-ray absorption spectroscopy reveal the actual active sites along with their dynamics and synergistic mechanisms in various electrolytes. Specially, Mn sites have strong binding affinity to hydroxyl groups, which enhances the water dissociation process at Pd sites with low energy barrier while Rh sites with optimal hydrogen adsorption free energy accelerate hydride coupling, thereby markedly boosting its intrinsic ability for hydrogen production.

Fine Engineering of d-Orbital Vacancies of ZnN4 via High-Shell Metal and Nonmetal Single-Atoms for Efficient and Poisoning-Resistant ORR

Atomically dispersed metal-nitrogen-carbon (M-N-C) materials are active oxygen reduction reaction (ORR) catalysts. Among M-N-C catalysts, ZnN4 single-atom catalysts (SACs) due to a nearly full 3d10 electronic configuration insufficiently activate oxygen and display low ORR activity. To finely engineer d-orbital vacancies of ZnN4, we combine high-shell metal and nonmetal SAs as electronic regulators that are ZnN4Cl and carbon vacancy-hosted -Cl motifs, which show complementary electron-withdrawing capacities versus the ZnN4. Under that, the ZnN4 exhibits significantly enhanced ORR activity with a half-wave potential (E1/2) of 0.912 VRHE relative to the unmodified ZnN4 (E1/2 = 0.822 VRHE) and simultaneously robust durability (negligible activity loss after 10,000 potential cycles). Particularly, the engineered ZnN4 possesses high resistance to SCN- poisoning, which is rarely achieved among M-N-C SACs. Our works show that combining high-shell metal and nonmetal SAs can finely engineer d-orbital vacancies of metal centers to an optimal state, thereby intrinsically enhancing their catalytic performance.

Periodic Single-Metal Site Catalysts: Creating Homogeneous and Ordered Atomic-Precision Structures

Heterogeneous single-metal-site catalysts (SMSCs), often referred to as single-atom catalysts (SACs), demonstrate promising catalytic activity, selectivity, and stability across a wide spectrum of reactions due to their rationally designed microenvironments encompassing coordination geometry, binding ligands, and electronic configurations. However, the inherent disorderliness of SMSCs at both atomic scale and nanoscale poses challenges in deciphering working principles and establishing the correlations between microenvironments and the catalytic performances of SMSCs. The rearrangement of randomly dispersed single metals into homogeneous and atomic-precisely structured periodic single-metal site catalysts (PSMSCs) not only simplifies the chaos in SMSCs systems but also unveils new opportunities for manipulating catalytic performance and gaining profound insights into reaction mechanisms. Moreover, the synergistic effects of adjacent single metals and the integration effects of periodic single-metal arrangement further broaden the industrial application scope of SMSCs. This perspective offers a comprehensive overview of recent advancements and outlines prospective avenues for research in the design and characterizations of PSMSCs, while also acknowledging the formidable challenges encountered and the promising prospects that lie ahead.

Challenges and Opportunities for Single-Atom Electrocatalysts: From Lab-Scale Research to Potential Industry-Level Applications

Single-atom electrocatalysts (SACs) are a class of promising materials for driving electrochemical energy conversion reactions due to their intrinsic advantages, including maximum metal utilization, well-defined active structures, and strong interface effects. However, SACs have not reached full commercialization for broad industrial applications. This review summarizes recent research achievements in the design of SACs for crucial electrocatalytic reactions on their active sites, coordination, and substrates, as well as the synthesis methods. The key challenges facing SACs in activity, selectivity, stability, and scalability, are highlighted. Furthermore, it is pointed out the new strategies to address these challenges including increasing intrinsic activity of metal sites, enhancing the utilization of metal sites, improving the stability, optimizing the local environment, developing new fabrication techniques, leveraging insights from theoretical studies, and expanding potential applications. Finally, the views are offered on the future direction of single-atom electrocatalysis toward commercialization.

Machine learning-based design of electrocatalytic materials towards high-energy lithium||sulfur batteries development

The practical development of Li | |S batteries is hindered by the slow kinetics of polysulfides conversion reactions during cycling. To circumvent this limitation, researchers suggested the use of transition metal-based electrocatalytic materials in the sulfur-based positive electrode. However, the atomic-level interactions among multiple electrocatalytic sites are not fully understood. Here, to improve the understanding of electrocatalytic sites, we propose a multi-view machine-learned framework to evaluate electrocatalyst features using limited datasets and intrinsic factors, such as corrected d orbital properties. Via physicochemical characterizations and theoretical calculations, we demonstrate that orbital coupling among sites induces shifts in band centers and alterations in the spin state, thus influencing interactions with polysulfides and resulting in diverse Li-S bond breaking and lithium migration barriers. Using a carbon-coated Fe/Co electrocatalyst (synthesized using recycled Li-ion battery electrodes as raw materials) at the positive electrode of a Li | |S pouch cell with high sulfur loading and lean electrolyte conditions, we report an initial specific energy of 436 Wh kg-1 (whole mass of the cell) at 67 mA and 25 °C.

Cohesive energy discrepancy drives the fabrication of multimetallic atomically dispersed materials for hydrogen evolution reaction

Atomically dispersed single atom (SA) and atomic cluster (AC) metallic materials attract tremendous attentions in various fields. Expanding monometallic SA and AC to multimetallic SA/AC composites opens vast scientific and technological potentials yet exponentially increasing the synthesis difficulty. Here, we present a general energy-selective-clustering methodology to build the largest reported library of carbon supported bi-/multi-metallic SA/AC materials. The discrepancy in cohesive energy results into selective metal clustering thereby driving the symbiosis of multimetallic SA or/and AC. The library includes 23 bimetallic SA/AC composites, and expanded compositional space of 17 trimetallic, quinary-metallic, septenary-metallic SA/AC composites. We chose bimetallic M1SAM2AC to demonstrate the electrocatalysis utility. Unique decoupled active sites and inter-site synergy lead to 8/47 mV overpotential at 10 mA cm-2 for alkaline/acidic hydrogen evolution and over 1000 h durability in water electrolyzer. Moreover, delicate modulations towards composition and configuration yield high-performance catalysts for multiple electrocatalysis systems. Our work broadens the family of atomically dispersed materials from monometallic to multimetallic and provides a platform to explore the complex composition induced unconventional effects.

The Micron-Droplet-Confined Continuous-Flow Synthesis of Freestanding High-Entropy-Alloy Nanoparticles by Flame Spray Pyrolysis

Alloying multiple immiscible elements into a nanoparticle with single-phase solid solution structure (high-entropy-alloy nanoparticles, HEA-NPs) merits great potential. To date, various kinds of synthesis techniques of HEA-NPs are developed; however, a continuous-flow synthesis of freestanding HEA-NPs remains a challenge. Here a micron-droplet-confined strategy by flame spray pyrolysis (FSP) to achieve the continuous-flow synthesis of freestanding HEA-NPs, is proposed. The continuous precursor solution undergoes gas shearing and micro-explosion to form nano droplets which act as the micron-droplet-confined reactors. The ultrafast evolution (<5 ms) from droplets to <10 nm nanoparticles of binary to septenary alloys is achieved through thermodynamic and kinetic control (high temperature and ultrafast colling). Among them, the AuPtPdRuIr HEA-NPs exhibit excellent electrocatalytic performance for alkaline hydrogen evolution reaction with 23 mV overpotential to achieve 10 mA cm-2, which is twofold better than that of the commercial Pt/C. It is anticipated that the continuous-flow synthesis by FSP can introduce a new way for the continuous synthesis of freestanding HEA-NP with a high productivity rate.

Novel amorphous FeOOH-modified Co9S8 nanosheets with enhanced catalytic activity in oxygen evolution reaction

Efficient oxygen evolution reaction (OER) is vital for water electrolysis and advanced hydrogen energy production. However, the sluggish kinetics of this reaction require significant overpotentials, leading to high energy consumption. Therefore, developing OER electrocatalysts with exceptional performance and long-term durability is crucial for enhancing the energy efficiency and cost-effectiveness of the hydrogen production process. In this research, novel FeOOH/Co9S8 catalysts were prepared through a two-step hydrothermal reaction followed by one-step electrodeposition on nickel foam for an alkaline OER. The as-obtained catalysts possessed abundant non-homogeneous interfaces between FeOOH and Co9S8 nanosheets, conducive to optimized coordination environments of Fe and Co sites by redistributing interfacial charges. This synergy strengthened the chemisorption of oxygenated intermediates, leading to accelerated reaction kinetics, abundant active sites, and enhanced OER performance. The optimized electrocatalyst FeOOH/Co9S8-15 achieved a current density of 10 mA cm-2 at an overpotential of 248 mV and good stability for over 140 h. This study presents a novel approach for producing compelling and durable alkaline dielectric OER electrocatalysts, which will be helpful in the future manufacturing of advanced energy devices.

Electronic redistribution induced by interaction between ruthenium nanoparticles and Ni-N(O)-C sites boosts alkaline water electrolysis

Ultrafine ruthenium nanoparticles are encapsulated by single-atom Ni-bonded graphitic carbon nitride (g-C3N4) layers anchored on carbon nanotubes (Ru/Ni-CNCT). The enhanced electronic interaction between Ru nanoparticles and Ni-N(O)-C sites anchored in g-C3N4 layers promotes water adsorption/dissociation and hydrogen evolution.

Creating High-entropy Single Atoms on Transition Disulfides through Substrate-induced Redox Dynamics for Efficient Electrocatalytic Hydrogen Evolution

The controllable anchoring of multiple metal single-atoms (SAs) into a single support exhibits scientific and technological opportunities, while marrying the concentration-complex multimetallic SAs and high-entropy SAs (HESAs) into one SAC system remains a substantial challenge. Here, we present a substrate-mediated SAs formation strategy to successfully fabricate a library of multimetallic SAs and HESAs on MoS2 and MoSe2 supports, which can precisely control the doping location of SAs. Specially, the contents of SAs can continuously increase until the accessible Mo atoms on TMDs carriers are completely replaced by SAs, thus allowing the of much higher metal contents. In-depth mechanistic study shows that the well-controlled synthesis of multimetallic SAs and HESAs is realized by controlling the reversible redox reaction occurred on the TMDs/TM ion interface. As a proof-of-concept application, a variety of SAs-TMDs were applied to hydrogen evolution reaction. The optimized HESAs-TMDs (Pt,Ru,Rh,Pd,Re-MoSe2) delivers a much higher activity and durability than state of-the-art Pt. Thus, our work will broaden the family of single-atom catalysts and provide a new guideline for the rational design of high-performance single-atom catalysts.

Oxygen-bridging Fe, Co dual-metal dimers boost reversible oxygen electrocatalysis for rechargeable Zn-air batteries

Rechargeable zinc-air batteries (ZABs) are regarded as a remarkably promising alternative to current lithium-ion batteries, addressing the requirements for large-scale high-energy storage. Nevertheless, the sluggish kinetics involving oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) hamper the widespread application of ZABs, necessitating the development of high-efficiency and durable bifunctional electrocatalysts. Here, we report oxygen atom-bridged Fe, Co dual-metal dimers (FeOCo-SAD), in which the active site Fe-O-Co-N6 moiety boosts exceptional reversible activity toward ORR and OER in alkaline electrolytes. Specifically, FeOCo-SAD achieves a half-wave potential (E1/2) of 0.87 V for ORR and an overpotential of 310 mV at a current density of 10 mA cm-2 for OER, with a potential gap (ΔE) of only 0.67 V. Meanwhile, FeOCo-SAD manifests high performance with a peak power density of 241.24 mW cm-2 in realistic rechargeable ZABs. Theoretical calculations demonstrate that the introduction of an oxygen bridge in the Fe, Co dimer induced charge spatial redistribution around Fe and Co atoms. This enhances the activation of oxygen and optimizes the adsorption/desorption dynamics of reaction intermediates. Consequently, energy barriers are effectively reduced, leading to a strong promotion of intrinsic activity toward ORR and OER. This work suggests that oxygen-bridging dual-metal dimers offer promising prospects for significantly enhancing the performance of reversible oxygen electrocatalysis and for creating innovative catalysts that exhibit synergistic effects and electronic states.

Electrocatalytic Oxygen Reduction Using Metastable Zirconium Suboxide

Strategies for discovery of high-performance electrocatalysts are important to advance clean energy technologies. Metastable phases such as low temperature or interfacial structures that are difficult to access in bulk may offer such catalytically active surfaces. We report here that the suboxide Zr3O, which is formed at Zr-ZrO2 interfaces but does not appear in the experimental Zr-O phase diagram exhibits outstanding oxygen reduction reaction (ORR) performance surpassing that of benchmark Pt/C and most transition metal-based catalysts. Addition of Fe3C nanoparticles to give a Zr-Zr3O-Fe3C/NC catalyst (NC=nitrogen-doped carbon) gives a half-wave potential (E1/2) of 0.914 V, outperforming Pt/C and showing only a 3 mV decrease after 20,000 electrochemical cycles. A zinc-air battery (ZAB) using this cathode material has a high power density of 241.1 mW cm-2 and remains stable for over 50 days of continuous cycling, demonstrating potential for practical applications. Zr3O demonstrates that interfacial or other phases that are difficult to stabilize may offer new directions for the discovery of high-performance electrocatalysts.

Type-printable photodetector arrays for multichannel meta-infrared imaging

Multichannel meta-imaging, inspired by the parallel-processing capability of neuromorphic computing, offers considerable advancements in resolution enhancement and edge discrimination in imaging systems, extending even into the mid- to far-infrared spectrum. Currently typical multichannel infrared imaging systems consist of separating optical gratings or merging multi-cameras, which require complex circuit design and heavy power consumption, hindering the implementation of advanced human-eye-like imagers. Here, we present printable graphene plasmonic photodetector arrays driven by a ferroelectric superdomain for multichannel meta-infrared imaging with enhanced edge discrimination. The fabricated photodetectors exhibited multiple spectral responses with zero-bias operation by directly rescaling the ferroelectric superdomain instead of reconstructing the separated gratings. We also demonstrated enhanced and faster shape classification (98.1%) and edge detection (98.2%) using our multichannel infrared images compared with single-channel detectors. Our proof-of-concept photodetector arrays simplify multichannel infrared imaging systems and offer potential solutions in efficient edge detection in human-brain-type machine vision.

Controllable synthesis of high-entropy alloys

High-entropy alloys (HEAs) involving more than four elements, as emerging alloys, have brought about a paradigm shift in material design. The unprecedented compositional diversities and structural complexities of HEAs endow multidimensional exploration space and great potential for practical benefits, as well as a formidable challenge for synthesis. To further optimize performance and promote advanced applications, it is essential to synthesize HEAs with desired characteristics to satisfy the requirements in the application scenarios. The properties of HEAs are highly related to their chemical compositions, microstructure, and morphology. In this review, a comprehensive overview of the controllable synthesis of HEAs is provided, ranging from composition design to morphology control, structure construction, and surface/interface engineering. The fundamental parameters and advanced characterization related to HEAs are introduced. We also propose several critical directions for future development. This review can provide insight and an in-depth understanding of HEAs, accelerating the synthesis of the desired HEAs.

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

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

Catalytically Active Carbon for Oxygen Reduction Reaction in Energy Conversion: Recent Advances and Future Perspectives

The shortage and unevenness of fossil energy sources are affecting the development and progress of human civilization. The technology of efficiently converting material resources into energy for utilization and storage is attracting the attention of researchers. Environmentally friendly biomass materials are a treasure to drive the development of new-generation energy sources. Electrochemical theory is used to efficiently convert the chemical energy of chemical substances into electrical energy. In recent years, significant progress has been made in the development of green and economical electrocatalysts for oxygen reduction reaction (ORR). Although many reviews have been reported around the application of biomass-derived catalytically active carbon (CAC) catalysts in ORR, these reviews have only selected a single/partial topic (including synthesis and preparation of catalysts from different sources, structural optimization, or performance enhancement methods based on CAC catalysts, and application of biomass-derived CACs) for discussion. There is no review that systematically addresses the latest progress in the synthesis, performance enhancement, and applications related to biomass-derived CAC-based oxygen reduction electrocatalysts synchronously. This review fills the gap by providing a timely and comprehensive review and summary from the following sections: the exposition of the basic catalytic principles of ORR, the summary of the chemical composition and structural properties of various types of biomass, the analysis of traditional and the latest popular biomass-derived CAC synthesis methods and optimization strategies, and the summary of the practical applications of biomass-derived CAC-based oxidative reduction electrocatalysts. This review provides a comprehensive summary of the latest advances to provide research directions and design ideas for the development of catalyst synthesis/optimization and contributes to the industrialization of biomass-derived CAC electrocatalysis and electric energy storage.

Atomic Engineering of Single-Atom Nanozymes for Biomedical Applications

Single-atom nanozymes (SAzymes) showcase not only uniformly dispersed active sites but also meticulously engineered coordination structures. These intricate architectures bestow upon them an exceptional catalytic prowess, thereby captivating numerous minds and heralding a new era of possibilities in the biomedical landscape. Tuning the microstructure of SAzymes on the atomic scale is a key factor in designing targeted SAzymes with desirable functions. This review first discusses and summarizes three strategies for designing SAzymes and their impact on reactivity in biocatalysis. The effects of choices of carrier, different synthesis methods, coordination modulation of first/second shell, and the type and number of metal active centers on the enzyme-like catalytic activity are unraveled. Next, a first attempt is made to summarize the biological applications of SAzymes in tumor therapy, biosensing, antimicrobial, anti-inflammatory, and other biological applications from different mechanisms. Finally, how SAzymes are designed and regulated for further realization of diverse biological applications is reviewed and prospected. It is envisaged that the comprehensive review presented within this exegesis will furnish novel perspectives and profound revelations regarding the biomedical applications of SAzymes.

Strategies Toward High Selectivity, Activity, and Stability of Single-Atom Catalysts

Single-atom catalysts (SACs) hold immense promise in facilitating the rational use of metal resources and achieving atomic economy due to their exceptional atom-utilization efficiency and distinct characteristics. Despite the growing interest in SACs, only limited reviews have holistically summarized their advancements centering on performance metrics. In this review, first, a thorough overview on the research progress in SACs is presented from a performance perspective and the strategies, advancements, and intriguing approaches employed to enhance the critical attributes in SACs are discussed. Subsequently, a comprehensive summary and critical analysis of the electrochemical applications of SACs are provided, with a particular focus on their efficacy in the oxygen reduction reaction , oxygen evolution reaction, hydrogen evolution reaction , CO2 reduction reaction, and N2 reduction reaction . Finally, the outline future research directions on SACs by concentrating on performance-driven investigation, where potential areas for improvement are identified and promising avenues for further study are highlighted, addressing challenges to unlock the full potential of SACs as high-performance catalysts.

High-entropy engineering with regulated defect structure and electron interaction tuning active sites for trifunctional electrocatalysis

High-entropy alloy nanoparticles (HEANs) possessing regulated defect structure and electron interaction exhibit a guideline for constructing multifunctional catalysts. However, the microstructure-activity relationship between active sites of HEANs for multifunctional electrocatalysts is rarely reported. In this work, HEANs distributed on multi-walled carbon nanotubes (HEAN/CNT) are prepared by Joule heating as an example to explain the mechanism of trifunctional electrocatalysis for oxygen reduction, oxygen evolution, and hydrogen evolution reaction. HEAN/CNT excels with unmatched stability, maintaining a 0.8V voltage window for 220 h in zinc-air batteries. Even after 20 h of water electrolysis, its performance remains undiminished, highlighting exceptional endurance and reliability. Moreover, the intrinsic characteristics of the defect structure and electron interaction for HEAN/CNT are investigated in detail. The electrocatalytic mechanism of trifunctional electrocatalysis of HEAN/CNT under different conditions is identified by in situ monitoring and theoretical calculation. Meanwhile, the electron interaction and adaptive regulation of active sites in the trifunctional electrocatalysis of HEANs were further verified by density functional theory. These findings could provide unique ideas for designing inexpensive multifunctional high-entropy electrocatalysts.

Engineering Symmetry-Breaking Centers and d-Orbital Modulation in Triatomic Catalysts for Zinc-Air Batteries

Unraveling the configuration-activity relationship and synergistic enhancement mechanism (such as real active center, electron spin-state, and d-orbital energy level) for triatomic catalysts, as well as their intrinsically bifunctional oxygen electrocatalysis, is a great challenge. Here we present a triatomic catalyst (TAC) with a trinuclear active structure that displays extraordinary oxygen electrocatalysis for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), greatly outperforming the counterpart of single-atom and diatomic catalysts. The aqueous Zn-air battery (ZAB) equipped with a TAC-based cathode exhibits extraordinary rechargeable stability and ultrarobust cycling performance (1970 h/3940 cycles at 2 mA cm-2, 125 h/250 cycles at 10 mA cm-2 with negligible voltage decay), and the quasi-solid-state ZAB displays outstanding rechargeability and low-temperature adaptability (300 h/1800 cycles at 2 mA cm-2 at -60 °C), outperforming other state-of-the-art ZABs. The experimental and theoretical analyses reveal the symmetry-breaking CoN4 configuration under incorporation of neighboring metal atoms (Fe and Cu), which leads to d-orbital modulation, a low-shift d band center, weakened binding strength to the oxygen intermediates, and decreased energy barrier for bifunctional oxygen electrocatalysis. This rational tricoordination design as well as an in-depth mechanism analysis indicate that hetero-TACs can be promisingly applied in various electrocatalysis applications.

Understanding the improvement mechanism of plasma etching treatment on oxygen reduction reaction catalysts

Plasma etching treatment is an effective strategy to improve the electrocatalytic activity, but the improvement mechanism is still unclear. In this work, a nitrogen-doped carbon nanotube-encased iron nanoparticles (Fe@NCNT) catalyst is synthesized as the model catalyst, followed by plasma etching treatment with different parameters. The electrocatalytic activity improvement mechanism of the plasma etching treatment is revealed by combining the physicochemical characterizations and electrochemical results. As a result, highly active metal-nitrogen species introduced by nitrogen plasma etching treatment are recognized as the main contribution to the improved electrocatalytic activity, and the defects induced by plasma etching treatment also contribute to the improvement of the electrocatalytic activity. In addition, the prepared catalyst also demonstrates superior ORR activity and stability than the commercial Pt/C catalyst.

Precise Design and Modification Engineering of Single-Atom Catalytic Materials for Oxygen Reduction

Due to their unique electronic and structural properties, single-atom catalytic materials (SACMs) hold great promise for the oxygen reduction reaction (ORR). Coordinating environmental and engineering strategies is the key to improving the ORR performance of SACMs. This review summarizes the latest research progress and breakthroughs of SACMs in the field of ORR catalysis. First, the research progress on the catalytic mechanism of SACMs acting on ORR is reviewed, including the latest research results on the origin of SACMs activity and the analysis of pre-adsorption mechanism. The study of the pre-adsorption mechanism is an important breakthrough direction to explore the origin of the high activity of SACMs and the practical and theoretical understanding of the catalytic process. Precise coordination environment modification, including in-plane, axial, and adjacent site modifications, can enhance the intrinsic catalytic activity of SACMs and promote the ORR process. Additionally, several engineering strategies are discussed, including multiple SACMs, high loading, and atomic site confinement. Multiple SACMs synergistically enhance catalytic activity and selectivity, while high loading can provide more active sites for catalytic reactions. Overall, this review provides important insights into the design of advanced catalysts for ORR.

Inductive Effect on Single-Atom Sites

Single-atom catalysts exhibit promising electrocatalytic activity, a trait that can be further enhanced through the introduction of heteroatom doping within the carbon skeleton. Nonetheless, the intricate relationship between the doping positions and activity remains incompletely elucidated. This contribution sheds light on an inductive effect of single-atom sites, showcasing that the activity of the oxygen reduction reaction (ORR) can be augmented by reducing the spatial gap between the doped heteroatom and the single-atom sites. Drawing inspiration from this inductive effect, we propose a synthesis strategy involving ligand modification aimed at precisely adjusting the distance between dopants and single-atom sites. This precise synthesis leads to optimized electrocatalytic activity for the ORR. The resultant electrocatalyst, characterized by Fe-N3P1 single-atom sites, demonstrates remarkable ORR activity, thus exhibiting great potential in zinc-air batteries and fuel cells.

Structural Self-Regulation-Promoted NO Electroreduction on Single Atoms

Simultaneously elevating loading and activity of single atoms (SAs) is desirable for SA-containing catalysts, including single-atom catalysts (SACs). However, the fast self-nucleation of SAs limits the loading, and the activity is confined by the adsorption-energy scaling relationships on monotonous SAs. Here, we theoretically design a novel type of SA-containing catalyst generated by two-step structural self-regulation. In the thermodynamic self-regulation step, divacancies in graphene spontaneously pull up SAs from transition metal supports (dv-g/TM; TM = fcc Co, hcp Co, Ni, Cu), leading to the expectably high loading of SAs. The subsequent kinetic self-regulation step involving an adsorbate-assisted and reversible vacancy migration dynamically alters coordination environments of SAs, helping circumvent the scaling relationships, and consequently, the as-designed dv-g/Ni can catalyze NO-to-NH3 conversion at a low limiting potential of -0.25 V vs RHE.

Multimetallic Single-Atom Catalysts for Bifunctional Oxygen Electrocatalysis

Multimetallic alloys have demonstrated promising performance for the application of metal-air batteries, while it remains a challenge to design multimetallic single-atom catalysts (MM-SACs). Herein, metal-C3N4 and nitrogen-doped carbon are employed as cornerstones to synthesize MM-SACs by a general two-step method, and the inherent features of atomic dispersion and the strong electronic reciprocity between the multimetallic sites have been verified. The trimetallic FeCoZn-SACs and quatermetallic FeCoCuZn-SACs are both found to deliver superior oxygen evolution reaction and oxygen reduction reaction activity, respectively, as well as outstanding bifunctional durability. Density functional theory calculations elucidate the crucial contribution of Co sites of FeCoCuZn-SACs to the efficient catalysis of both the ORR and the OER. More importantly, Zn-air batteries with FeCoCuZn-SACs as cathodic catalysts exhibit a high power density (252 mW cm-2), high specific capacity (817 mAh gZn-1), and considerable stability (over 225 h) for charging-discharging processes. This work provides a visual perspective for the advantages of MM-SACs toward oxygen electrocatalysis.

Sustainable zinc-air battery chemistry: advances, challenges and prospects

Sustainable zinc-air batteries (ZABs) are considered promising energy storage devices owing to their inherent safety, high energy density, wide operating temperature window, environmental friendliness, etc., showing great prospect for future large-scale applications. Thus, tremendous efforts have been devoted to addressing the critical challenges associated with sustainable ZABs, aiming to significantly improve their energy efficiency and prolong their operation lifespan. The growing interest in sustainable ZABs requires in-depth research on oxygen electrocatalysts, electrolytes, and Zn anodes, which have not been systematically reviewed to date. In this review, the fundamentals of ZABs, oxygen electrocatalysts for air cathodes, physicochemical properties of ZAB electrolytes, and issues and strategies for the stabilization of Zn anodes are systematically summarized from the perspective of fundamental characteristics and design principles. Meanwhile, significant advances in the in situ/operando characterization of ZABs are highlighted to provide insights into the reaction mechanism and dynamic evolution of the electrolyte|electrode interface. Finally, several critical thoughts and perspectives are provided regarding the challenges and opportunities for sustainable ZABs. Therefore, this review provides a thorough understanding of the advanced sustainable ZAB chemistry, hoping that this timely and comprehensive review can shed light on the upcoming research horizons of this prosperous area.

Understanding the Bifunctional Trends of Fe-Based Binary Single-Atom Catalysts

Binary single-atom catalysts (BSACs) have demonstrated fascinating activities compared to single atom catalysts (SACs) for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Notably, Fe SACs is one of the most promising ORR electrocatalysts, and further revealing the synergistic effects between Fe and other 3d transition metals (M) for FeM BSACs are very important to enhance bifunctional performance. Herein, density functional theory (DFT) calculations are first adapted to demonstrate the role of various transition metals on the bifunctional activity of Fe sites, and a notable volcano relationship is established through the generally accepted adsorption free energy that ΔG* OH for ORR, and ΔG* O -ΔG* OH for OER, respectively. Further, ten of the atomically dispersed FeM anchored on nitrogen-carbon support (FeM-NC) are successfully synthesized with typical atomic dispersion by a facile movable type printing method. The experimental data confirms the bifunctional activity diversity of FeM-NC between the early- and late- transition metals, agrees very well with the DFT results. More importantly, the optimal FeCu-NC shows the expected performance with high ORR and OER activity, thereby, the assembled rechargeable zinc-air battery delivers a high power density of 231 mW cm-2 , and an impressive stability that can be stably operated over 300 h.

Understanding the selection of catalytic pathway on graphene-supported nitrogen coordinated Ru-atom by ab initio molecular dynamics simulation

CONTEXT

In the paper, the ORR/OER on graphene-supported nitrogen coordinated Ru-atom (Ru-N-C) is simulated. We discuss nitrogen coordination influences electronic properties, adsorption energies, and catalytic activity in a single-atom Ru active site. The over potentials on Ru-N-C are 1.12 eV/1.00 eV for ORR/OER. We calculate Gibbs-free energy (ΔG) for every reaction step in ORR/OER process. In order to gain a deeper understanding of the catalytic process on the surface of single atom catalysts, the ab initio molecular dynamics (AIMD) simulations show that Ru-N-C has a structural stability at 300 K and that ORR/OER on Ru-N-C can occur along a typical four-electron process of reaction. AIMD simulations of catalytic processes provide detailed information about atom interactions.

METHODS

In this paper, we use density functional theory (DFT) with PBE functional to study the electronic properties and adsorption properties of graphene-supported nitrogen coordinated Ru-atom (Ru-N-C) Gibbs-free energy and Gibbs-free energy for very reaction step. The structural optimization and all the calculations are carried out by Dmol3 package, adopting the PNT basis set and DFT semicore pseudopotential. Ab initio molecular dynamics simulations (AIMD) were run for 10 ps. The canonical (NVT) ensemble, massive GGM thermostat, and a temperature of 300 K are taken into account. The functional of B3LYP and the DNP basis set are chosen for AIMD.

Heterointerface promoted trifunctional electrocatalysts for all temperature high-performance rechargeable Zn-air batteries

The rational design of wide-temperature operating Zn-air batteries is crucial for their practical applications. However, the fundamental challenges remain; the limitation of the sluggish oxygen redox kinetics, insufficient active sites, and poor efficiency/cycle lifespan. Here we present heterointerface-promoted sulfur-deficient cobalt-tin-sulfur (CoS_1-δ/SnS_2-δ) trifunctional electrocatalysts by a facile solvothermal solution-phase approach. The CoS_1-δ/SnS_2-δ displays superb trifunctional activities, precisely a record-level oxygen bifunctional activity of 0.57 V (E_1/2 = 0.90 V and E_j=10 = 1.47 V) and a hydrogen evolution overpotential (41 mV), outperforming those of Pt/C and RuO₂. Theoretical calculations reveal the modulation of the electronic structures and d-band centers that endorse fast electron/proton transport for the hetero-interface and avoid the strong adsorption of intermediate species. The alkaline Zn-air batteries with CoS_1-δ/SnS_2-δ manifest record-high power density of 249 mW cm^-2 and long-cycle life for >1000 cycles under harsh operations of 20 mA cm^-2, surpassing those of Pt/C + RuO₂ and previous state-of-the-art catalysts. Furthermore, the solid-state flexible Zn-air battery also displays remarkable performance with an energy density of 1077 Wh kg^-1, >690 cycles for 50 mA cm^-2, and a wide operating temperature from +80 to -40 °C with 85% capacity retention, which provides insights for practical Zn-air batteries.

Synthesis of Phase Junction Cadmium Sulfide Photocatalyst under Sulfur-Rich Solution System for Efficient Photocatalytic Hydrogen Evolution

Photocatalyst with excellent semiconductor properties is the key point to realize the efficient photocatalytic hydrogen evolution (PHE). As a representative binary metal sulfide (BMS) semiconductor, cadmium sulfide (CdS) possesses suitable bandgap of 2.4 eV and negative conduction band potential, which has a great potential to realize efficient visible-light PHE performance. In this work, CdS with unique cubic/hexagonal phase junction is facilely synthesized through a sulfur-rich butyldithiocarbamate acid (BDCA) solution process. The results illustrate that the phase junction can efficiently enhance the separation and transfer of photogenerated electron-hole pairs, resulting in an excellent PHE performance. In addition, the sulfur-rich property of BDCA solution leads to the absence of additional sulfur sources during the synthesis of CdS photocatalyst, which greatly simplifies the fabrication process. The optimal PHE rate of the BDCA-synthesized phase junction CdS photocatalyst is 7.294 mmol g^-1  h^-1 and exhibits a favorable photostability. Moreover, density function theory calculations indicated that the apparent redistribution of charge density in the cubic/hexagonal phase junction regions gives a suitable hydrogen adsorption capacity, which is responsible for the enhanced PHE activity.

Stabilizing High Density Cu Active Sites with ZrO2 Quantum Dots as Chemical Ligand in N-doped Porous Carbon Nanofibers for Efficient ORR

The emerging transition metal-nitrogen-carbon (MNC) materials are considered as a promising oxygen reduction reaction (ORR) catalyst system to substitute expensive Pt/C catalysts due to their high surface area and potential high catalytic activity. However, MNC catalysts are easy to be attacked by the ORR byproducts that easily lead to the deactivation of metal active sites. Moreover, a high metal loading affects the mass transfer and stability, but a low loading delivers inferior catalytic activity. Here, a new strategy of designing ZrO₂ quantum dots and N-complex as dual chemical ligands in N-doped bubble-like porous carbon nanofibers (N-BPCNFs) to stabilize copper (Cu) by forming CuZrO_3-x /ZrO₂ heterostructures and CuN ligands with a high loading of 40.5 wt.% is reported. While the highly porous architecture design of N-BPCNFs builds a large solidelectrolytegas phase interface and promotes mass transfer. The preliminary results show that the half-wave potential of the catalyst reaches 0.856 V, and only decreases 0.026 V after 10 000 cycles, exhibiting excellent stability. The proposed strategy of stabilizing metal active sites with both heterostructures and CuN ligands is feasible and scalable for developing high metal loading ORR catalyst.

One-Step Synthesis of a Non-Precious-Metal Tris (Fe/N/F)-Doped Carbon Catalyst for Oxygen Reduction Reactions

Advancements in inexpensive, efficient, and durable oxygen reduction catalysts is important for maintaining the sustainable development of fuel cells. Although doping carbon materials with transition metals or heteroatomic doping is inexpensive and enhances the electrocatalytic performance of the catalyst, because the charge distribution on its surface is adjusted, the development of a simple method for the synthesis of doped carbon materials remains challenging. Here, a non-precious-metal tris (Fe/N/F)-doped particulate porous carbon material (2₁P₂-Fe₁-850) was synthesized by employing a one-step process, using 2-methylimidazole, polytetrafluoroethylene, and FeCl₃ as raw materials. The synthesized catalyst exhibited a good oxygen reduction reaction performance with a half-wave potential of 0.85 V in an alkaline medium (compared with 0.84 V of commercial Pt/C). Moreover, it had better stability and methanol resistance than Pt/C. This was mainly attributed to the effect of the tris (Fe/N/F)-doped carbon material on the morphology and chemical composition of the catalyst, thereby enhancing the catalyst's oxygen reduction reaction properties. This work provides a versatile method for the gentle and rapid synthesis of highly electronegative heteroatoms and transition metal co-doped carbon materials.