Greatly Enhanced Oxygen Reduction Reaction in Anion Exchange Membrane Fuel Cell and Zn-Air Battery via Hole Inner Edge Reconstruction of 2D Pd Nanomesh

Platinum group metals (PGM) have yet to be the most active catalysts in various sustainable energy reactions. Their high cost, however, has made maximizing the activity and minimizing the dosage become an urgent priority for the practical applications of emerging technologies. Herein, a novel 2D Pd nanomesh structure possessing hole inner reconstructed edges (HIER) with exposed high energy facets and overstretched lattice parameters is fabricated through a facile room-temperature reduction method at gram-scale yields. The HIER enhances the catalytic performance of Pd in electrochemical oxygen reduction reaction (ORR), achieving superior mass activity (MA) of 2.672 A mgPd -1, which is 27.8 fold and 23.6 fold higher, respectively, than those of the commercial Pt/C (0.096 A mgPt -1) and Pd/C (0.113 A mgPd -1) at 0.9 VRHE. Most significantly, in H2-air anion exchange membrane fuel cell (AEMFC) and Zn-air battery (ZAB) applications, this unique Pd catalyst delivers a much-outperformed peak power density of 0.86 and 0.22 W cm-2, respectively, compared with 0.54 and 0.13 W cm-2 of the commercial Pt/C catalyst, indicating a novel pathway in electrocatalyst designs through HIER engineering.

Probing Basal and Prismatic Planes of Graphitic Materials for Metal Single Atom and Subnanometer Cluster Stabilization

Supported metal single atom catalysis is a dynamic research area in catalysis science combining the advantages of homogeneous and heterogeneous catalysis. Understanding the interactions between metal single atoms and the support constitutes a challenge facing the development of such catalysts, since these interactions are essential in optimizing the catalytic performance. For conventional carbon supports, two types of surfaces can contribute to single atom stabilization: the basal planes and the prismatic surface; both of which can be decorated by defects and surface oxygen groups. To date, most studies on carbon-supported single atom catalysts focused on nitrogen-doped carbons, which, unlike classic carbon materials, have a fairly well-defined chemical environment. Herein we report the synthesis, characterization and modeling of rhodium single atom catalysts supported on carbon materials presenting distinct concentrations of surface oxygen groups and basal/prismatic surface area. The influence of these parameters on the speciation of the Rh species, their coordination and ultimately on their catalytic performance in hydrogenation and hydroformylation reactions is analyzed. The results obtained show that catalysis itself is an interesting tool for the fine characterization of these materials, for which the detection of small quantities of metal clusters remains a challenge, even when combining several cutting-edge analytical methods.

A Redox-Active Iron-Organic Framework Cathodes for Sustainable Magnesium Metal Batteries

Rechargeable magnesium metal batteries (RMBs) have shown promising prospects in sustainable energy storage due to the high crustal abundance, safety, and potentially large specific capacity of magnesium. However, their development is constrained by the lack of effective cathode materials that can achieve high capacity and stable magnesium storage at a practically reasonable rate. Herein, we construct a three-dimensional (3D) iron(III)-dihydroxy-benzoquinone (Fe2(DHBQ)3) metal-organic framework (MOF) material with dual redox centers of Fe3+ cations and DHBQ2- anions for reversible storage of Mg2+ in RMBs. Spectroscopic analysis and density functional theory (DFT) calculations reveal the redox chemistry of both Fe3+ ions and carbonyls from DHBQ ligands during electrochemical processes. Benefiting from the rational structure, the Fe2(DHBQ)3∥Mg cells exhibit a high reversible capacity of 395.3 mAh/g, large energy density of 463.5 Wh/kg, and high power density of 2456.0 W/kg. Moreover, the high electronic conductivity (8.35 × 10-5 S/cm) and favorable diffusion path of Mg2+ in Fe2(DHBQ)3 endow the cells with exceptional cycling stability and rate capability with a long life of 5000 cycles at 2000 mA/g. The dual redox-active MOF demonstrates a category of advanced cathode materials for high-performance RMBs.

Mechanisms of the Accelerated Li+ Conduction in MOF-Based Solid-State Polymer Electrolytes for All-Solid-State Lithium Metal Batteries

Solid polymer electrolytes (SPEs) for lithium metal batteries have garnered considerable interests owing to their low cost, flexibility, lightweight, and favorable interfacial compatibility with battery electrodes. Their soft mechanical nature compared to solid inorganic electrolytes give them a large advantage to be used in low pressure solid-state lithium metal batteries, which can avoid the cost and weight of the pressure cages. However, the application of SPEs is hindered by their relatively low ionic conductivity. In addressing this limitation, enormous efforts are devoted to the experimental investigation and theoretical calculations/simulation of new polymer classes. Recently, metal-organic frameworks (MOFs) have been shown to be effective in enhancing ion transport in SPEs. However, the mechanisms in enhancing Li+ conductivity have rarely been systematically and comprehensively analyzed. Therefore, this review provides an in-depth summary of the mechanisms of MOF-enhanced Li+ transport in MOF-based solid polymer electrolytes (MSPEs) in terms of polymer, MOF, MOF/polymer interface, and solid electrolyte interface aspects, respectively. Moreover, the understanding of Li+ conduction mechanisms through employing advanced characterization tools, theoretical calculations, and simulations are also reviewed in this review. Finally, the main challenges in developing MSPEs are deeply analyzed and the corresponding future research directions are also proposed.

Understanding and Harnessing Nanoscale Immiscibility in Ru-In Alloys for Selective CO2 Hydrogenation

Bimetallic alloys made from immiscible elements are characterized by their tendency to segregate on the macroscopic scale, but their behavior is known to change at the nanoscale. Here, we demonstrate that in the Ru-In system, In atoms preferentially decorate the surface of 6 nm Ru nanoparticles, forming Ru-In superficial immiscible alloys. This surface decoration dramatically affects the catalytic performance of the system, even at small atomic fractions of In added to Ru. The interfaces between Ru and In enabled unexplored methanol productivity from CO2 hydrogenation, which outperformed not only the individual constituents but also ordered RuIn3 intermetallic alloys. Our work highlights that the formation of superficial immiscible alloys could offer new insights into the understanding and design of heterogeneous catalysts.

Synchrotron Radiation Based X-ray Absorption Spectroscopy: Fundamentals and Applications in Photocatalysis

Photocatalysis is one of the most promising green technologies to utilize solar energy for clean energy achievement and environmental governance. There is a knotty problem to rational designing high-performance photocatalyst, which largely depends on an in-depth insight into their structure-activity relationships and complex photocatalytic reaction mechanisms. Synchrotron radiation based X-ray absorption spectroscopy (XAS) is an important characterization method for photocatlayst to offer the element-specific key geometric and electronic structural information at the atomic level, on this basis, time-resolved XAS technique has a huge impact on mechanistic understanding of photochemical reaction owing to their powerful ability to probe, in real-time, the electronic and geometric structures evolution within photocatalysis reactions. This review will focus on the fundamentals of XAS and their applications in photocatalysis. The detailed applications obtained from XAS is described through the following aspects: 1) identifying local structure of photocatalyst; 2) uncovering in situ structure and chemical state evolution during photocatalysis; 3) revealing the photoexcited process. We will provide an in depth understanding on how the XAS method can guide the rational design of highly efficient photocatalyst. Finally, a systematic summary of XAS and related significance is made and the research perspectives are suggested.

Electrifying Energy and Chemical Transformations with Single-Atom Alloy Nanoparticle Catalysts

Single-atom alloys (SAAs) have attracted considerable attention as promising electrocatalysts in reactions central to energy conversion and chemical transformation. In contrast to monometallic nanocrystals and metal alloys, SAAs possess unique and intriguing physicochemical properties, positioning them as ideal model systems for studying structure-property relationships. However, the field is still in its early stages. In this Perspective, we first review and summarize rational synthesis methods and advanced characterization techniques for SAA nanoparticle catalysts. We then emphasize the extensive applications of SAAs in a range of electrocatalytic reactions, including fuel cell reactions, water splitting, and carbon dioxide and nitrate reductions. Finally, we provide insights into existing challenges and prospects associated with the controlled synthesis, characterization, and design of SAA catalysts.

Elucidating Local Structure and Positional Effect of Dopants in Colloidal Transition Metal Dichalcogenide Nanosheets for Catalytic Hydrogenolysis

Tailoring nanoscale catalysts to targeted applications is a vital component in reducing the carbon footprint of industrial processes; however, understanding and controlling the nanostructure influence on catalysts is challenging. Molybdenum disulfide (MoS2), a transition metal dichalcogenide (TMD) material, is a popular example of a nonplatinum-group-metal catalyst with tunable nanoscale properties. Doping with transition metal atoms, such as cobalt, is one method of enhancing its catalytic properties. However, the location and influence of dopant atoms on catalyst behavior are poorly understood. To investigate this knowledge gap, we studied the influence of Co dopants in MoS2 nanosheets on catalytic hydrodesulfurization (HDS) through a well-controlled, ligand-directed, tunable colloidal doping approach. X-ray absorption spectroscopy and density functional theory calculations revealed the nonmonotonous relationship between dopant concentration, location, and activity in HDS. Catalyst activity peaked at 21% Co:Mo as Co saturates the edge sites and begins basal plane doping. While Co prefers to dope the edges over basal sites, basal Co atoms are demonstrably more catalytically active than edge Co. These findings provide insight into the hydrogenolysis behavior of doped TMDs and can be extended to other TMD materials.

Atomic Design of Alkyne Semihydrogenation Catalysts via Active Learning

Alkyne hydrogenation on palladium-based catalysts modified with silver is currently used in industry to eliminate trace amounts of alkynes in alkenes produced from steam cracking and alkane dehydrogenation processes. Intensive efforts have been devoted to designing an alternative catalyst for improvement, especially in terms of selectivity and catalyst cost, which is still far away from that as expected. Here, we describe an atomic design of a high-performance Ni-based intermetallic catalyst aided by active machine learning combined with density functional theory calculations. The engineered NiIn catalyst exhibits >97% selectivity to ethylene and propylene at the full conversion of acetylene and propyne at mild temperature, outperforming the reported Ni-based catalysts and even noble Pd-based ones. Detailed mechanistic studies using theoretical calculations and advanced characterizations elucidate that the atomic-level defined coordination environment of Ni sites and well-designed hybridization of Ni 3d with In 5p orbital determine the semihydrogenation pathway.

Biomimetic Control over Bimetallic Nanoparticle Structure and Activity via Peptide Capping Ligand Sequence

The controlled design of bimetallic nanoparticles (BNPs) is a key goal in tailoring their catalytic properties. Recently, biomimetic pathways demonstrated potent control over the distribution of different metals within BNPs, but a direct understanding of the peptide effect on the compositional distribution at the interparticle and intraparticle levels remains lacking. We synthesized two sets of PtAu systems with two peptides and correlated their structure, composition, and distributions with the catalytic activity. Structural and compositional analyses were performed by a combined machine learning-assisted refinement of X-ray absorption spectra and Z-contrast measurements by scanning transmission electron microscopy. The difference in the catalytic activities between nanoparticles synthesized with different peptides was attributed to the details of interparticle distribution of Pt and Au across these markedly heterogeneous systems, comprising Pt-rich, Au-rich, and Au core/Pt shell nanoparticles. The total amount of Pt in the shells of the BNPs was proposed to be the key catalytic activity descriptor. This approach can be extended to other systems of metals and peptides to facilitate the targeted design of catalysts with the desired activity.

Visualizing the Birth and Monitoring the Life of a Bimetallic Methanation Catalyst

Well-defined bimetallic heterogeneous catalysts are not only difficult to synthesize in a controlled manner, but their elemental distributions are also notoriously challenging to define. Knowledge of these distributions is required for both the as-synthesized catalyst and its activated form under reaction conditions, where various types of reconstruction can occur. Success in this endeavor requires observation of the active catalyst via in situ analytical methods. As a step toward this goal, we present a composite material composed of bimetallic nickel-ruthenium nanoparticles supported on a protonated zeolite (Ni-Ru/HZSM-5) and probe its evolution and function as a photoactive carbon dioxide methanation catalyst using in situ X-ray absorption spectroscopy (XAS). The working Ni-Ru/HZSM-5, as a selective and durable photothermal CO2 methanation catalyst, comprises a corona of Ru nanoparticles decorating a Ni nanoparticle core. The specific Ni-Ru interactions in the bimetallic particles were confirmed by in situ XAS, which reveals significant electron transfer from Ni to Ru. The light-harvesting Ni nanoparticle core and electron-accepting Ru nanoparticle corona serve as the CO2 and H2 dissociation centers, respectively. These Ni and Ru nanoparticles also promote synergistic photothermal and hydrogen atom transfer effects. Collectively, these effects enable an associative CO2 methanation reaction pathway while hindering coking and fostering high selectivity toward methane.

Resolving Atomic-Scale Structure and Chemical Coordination in High-Entropy Alloy Electrocatalysts for Structure-Function Relationship Elucidation

The recent breakthrough in confining five or more atomic species in nanocatalysts, referred to as high-entropy alloy nanocatalysts (HEAs), has revealed the possibilities of multielemental interactions that can surpass the limitations of binary and ternary electrocatalysts. The wide range of potential surface configurations in HEAs, however, presents a significant challenge in resolving active structural motifs, preventing the establishment of structure-function relationships for rational catalyst design and optimization. We present a methodology for creating sub-5 nm HEAs using an aqueous-based peptide-directed route. Using a combination of pair distribution function and X-ray absorption spectroscopy, HEA structure models are constructed from reverse Monte Carlo modeling of experimental data sets and showcase a clear peptide-induced influence on atomic-structure and chemical miscibility. Coordination analysis of our structure models facilitated the construction of structure-function correlations applied to electrochemical methanol oxidation reactions, revealing the complex interplay between multiple metals that leads to improved catalytic properties. Our results showcase a viable strategy for elucidating structure-function relationships in HEAs, prospectively providing a pathway for future materials design.

Intermetallic Nanocrystals for Fuel-Cells-Based Electrocatalysis

Electrocatalysis underpins the renewable electrochemical conversions for sustainability, which further replies on metallic nanocrystals as vital electrocatalysts. Intermetallic nanocrystals have been known to show distinct properties compared to their disordered counterparts, and been long explored for functional improvements. Tremendous progresses have been made in the past few years, with notable trend of more precise engineering down to an atomic level and the investigation transferring into more practical membrane electrode assembly (MEA), which motivates this timely review. After addressing the basic thermodynamic and kinetic fundamentals, we discuss classic and latest synthetic strategies that enable not only the formation of intermetallic phase but also the rational control of other catalysis-determinant structural parameters, such as size and morphology. We also demonstrate the emerging intermetallic nanomaterials for potentially further advancement in energy electrocatalysis. Then, we discuss the state-of-the-art characterizations and representative intermetallic electrocatalysts with emphasis on oxygen reduction reaction evaluated in a MEA setup. We summarize this review by laying out existing challenges and offering perspective on future research directions toward practicing intermetallic electrocatalysts for energy conversions.

Atomic-level investigation on significance of photoreduced Pt nanoparticles over g-C3 N4 /bimetallic oxide composites

Designing an effective photocatalyst for solar-to-chemical fuel conversion presents significant challenges. Herein, g-C3 N4 nanotubes/CuCo2 O4 (CN-NT-CCO) composites decorated with platinum nanoparticles (Pt NPs) were successfully synthesized by chemical and photochemical reductions. The size distribution and location of Pt NPs on the surface of CN-NT-CCO composites were directly observed by TEM. Extended X-ray absorption fine structure (EXAFS) spectra of Pt L3-edge for the above composite confirmed establishment of Pt-N bonds at an atomic distance of 2.09 Å in the photoreduced Pt-bearing composite, which was shorter than in chemically reduced Pt-bearing composites. This proved the stronger interaction of photoreduced Pt NPs with the CN-NT-CCO composite than chemical reduced one. The H2 evolution performance of the photoreduced (PR) Pt@CN-NT-CCO (2079 μmol h-1  g-1 ) was greater than that of the chemically reduced (CR) Pt@CN-NT-CCO composite (1481 μmol h-1  g-1 ). The abundance of catalytically active sites and transfer of electrons from CN-NT to the Pt NPs to participate in the hydrogen evolution are the primary reasons for the improved performance. Furthermore, electrochemical investigations and band edge locations validated the presence of a Z-scheme heterojunction at the Pt@CN-NT-CCO interface. This work offers unique perspectives on the structure and interface design at the atomic level to fabricate high-performance heterojunction photocatalysts.

Intermetallic Single-Atom Alloy In-Pd Bimetallene for Neutral Electrosynthesis of Ammonia from Nitrate

Harvesting recyclable ammonia (NH₃) from the electrocatalytic reduction of nitrate (NO₃RR) offers a sustainable strategy to close the ecological nitrogen cycle from nitration contamination in an energy-efficient and environmentally friendly manner. The emerging intermetallic single-atom alloys (ISAAs) are recognized to achieve the highest site density of single atoms by isolating contiguous metal atoms into single sites stabilized by another metal within the intermetallic structure, which holds promise to couple the catalytic benefits from intermetallic nanocrystals and single-atom catalysts for promoting NO₃RR. Herein, ISAA In-Pd bimetallene, in which the Pd single atoms are isolated by surrounding In atoms, is reported to boost neutral NO₃RR with a NH₃ Faradaic efficiency (FE) of 87.2%, a yield rate of 28.06 mg h^-1 mg_Pd^-1, and an exceptional electrocatalytic stability with increased activity/selectivity over 100 h and 20 cycles. The ISAA structure induces substantially diminished overlap of Pd d-orbitals and narrowed p-d hybridization of In-p and Pd-d states around the Fermi level, resulting in a stronger NO₃^- adsorption and a depressed energy barrier of the potential-determining step for NO₃RR. Further integrating the NO₃RR catalyst into a Zn-NO₃^- flow battery as the cathode delivers a power density of 12.64 mW cm^-2 and a FE of 93.4% for NH₃ production.

Lattice Strain and Schottky Junction Dual Regulation Boosts Ultrafine Ruthenium Nanoparticles Anchored on a N-Modified Carbon Catalyst for H2 Production

Ruthenium-based materials are considered great promising candidates to replace Pt-based catalysts for hydrogen production in alkaline conditions. Herein, we adopt a facile method to rationally design a neoteric Schottky catalyst in which uniform ultrafine ruthenium nanoparticles featuring lattice compressive stress are supported on nitrogen-modified carbon nanosheets (Ru NPs/NC) for efficient hydrogen evolution reaction (HER). Lattice strain and Schottky junction dual regulation ensures that the Ru NPs/NC catalyst with an appropriate nitrogen content displays superb H₂ evolution in alkaline media. Particularly, Ru NPs/NC-900 with 1.3% lattice compressive strain displays attractive activity and durability for the HER with a low overpotential of 19 mV at 10 mA cm^-2 in 1.0 M KOH electrolyte. The in situ X-ray absorption fine structure measurements indicate that the low-valence Ru nanoparticle with shrinking Ru-Ru bond acts as catalytic active site during the HER process. Furthermore, multiple spectroscopy analysis and density functional theory calculations demonstrate that the lattice strain and Schottky junction dual regulation tunes the electron density and hydrogen adsorption of the active center, thus enhancing the HER activity. This strategy provides a novel concept for the design of advanced electrocatalysts for H₂ production.

Solution-Processed Inorganic Thermoelectric Materials: Opportunities and Challenges

Thermoelectric technology requires synthesizing complex materials where not only the crystal structure but also other structural features such as defects, grain size and orientation, and interfaces must be controlled. To date, conventional solid-state techniques are unable to provide this level of control. Herein, we present a synthetic approach in which dense inorganic thermoelectric materials are produced by the consolidation of well-defined nanoparticle powders. The idea is that controlling the characteristics of the powder allows the chemical transformations that take place during consolidation to be guided, ultimately yielding inorganic solids with targeted features. Different from conventional methods, syntheses in solution can produce particles with unprecedented control over their size, shape, crystal structure, composition, and surface chemistry. However, to date, most works have focused only on the low-cost benefits of this strategy. In this perspective, we first cover the opportunities that solution processing of the powder offers, emphasizing the potential structural features that can be controlled by precisely engineering the inorganic core of the particle, the surface, and the organization of the particles before consolidation. We then discuss the challenges of this synthetic approach and more practical matters related to solution processing. Finally, we suggest some good practices for adequate knowledge transfer and improving reproducibility among different laboratories.

Composition control of alloy nanoparticles consisting of bulk-immiscible Au and Rh metals via an ionic liquid/metal sputtering technique for improving their electrocatalytic activity

AuRh bimetallic alloy nanoparticles (NPs) were successfully prepared by simultaneous sputtering of Au and Rh in a room-temperature ionic liquid (RTIL) of N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium tetrafluoroborate (DEME-BF₄). Bimetallic AuRh alloy NPs of 1-2 nm in size were formed in the RTIL. The alloy composition was controllable by changing the surface areas of Au and Rh plates used as sputtering targets. Loading thus-obtained AuRh NPs on carbon black (CB) powders increased the size of AuRh NPs to ca. 2-8 nm, depending on the Au/Rh ratio. The electrocatalytic activity for oxygen reduction reaction (ORR) of AuRh NP-loaded CB catalysts showed a volcano-type dependence on their composition, in which AuRh NPs with Au surface coverage of 62% exhibited the optimal ORR activity, the specific activity being ca. 5 times higher than that of pure Rh NPs.

Mechanism driven design of trimer Ni1Sb2 site delivering superior hydrogenation selectivity to ethylene

Mechanism driven catalyst design with atomically uniform ensemble sites is an important yet challenging issue in heterogeneous catalysis associated with breaking the activity-selectivity trade-off. Herein, a trimer Ni₁Sb₂ site in NiSb intermetallic featuring superior selectivity is elaborated for acetylene semi-hydrogenation via a theoretical guidance with a precise synthesis strategy. The trimer Ni₁Sb₂ site in NiSb intermetallic is predicted to endow acetylene reactant with an adequately but not excessively strong σ-adsorption mode while ethylene product with a weak π-adsorption one, where such compromise delivers higher ethylene formation rate. An in-situ trapping of molten Sb by Ni strategy is developed to realize the construction of Ni₁Sb₂ site in the intermetallic P6₃/mmc NiSb catalysts. Such catalyst exhibits ethylene selectivity up to 93.2% at 100% of acetylene conversion, significantly prevailing over the referred Ni catalyst. These insights shed new lights on rational catalyst design by taming active sites to energetically match targeted reaction pathway.

Designing atomically uniform ensemble sites for matching targeted reaction pathway is important yet challenging in heterogeneous catalysis. Here, the authors fabricate a trimer Ni₁Sb₂ site featuring superior selectivity for acetylene semi-hydrogenation via a mechanism-driven design strategy.

The Inner Shell Spectroscopy beamline at NSLS-II: a facility for in situ and operando X-ray absorption spectroscopy for materials research

The Inner Shell Spectroscopy (ISS) beamline on the 8-ID station at the National Synchrotron Light Source II (NSLS-II), Upton, NY, USA, is a high-throughput X-ray absorption spectroscopy beamline designed for in situ, operando, and time-resolved material characterization using high monochromatic flux and scanning speed. This contribution discusses the technical specifications of the beamline in terms of optics, heat load management, monochromator motion control, and data acquisition and processing. Results of the beamline tests demonstrating the quality of the data obtainable on the instrument, possible energy scanning speeds, as well as long-term beamline stability are shown. The ability to directly control the monochromator trajectory to define the acquisition time for each spectral region is highlighted. Examples of studies performed on the beamline are presented. The paper is concluded with a brief outlook for future developments.

Structurally Precise Two-Transition-Metal Water Oxidation Catalysts: Quantifying Adjacent 3d Metals by Synchrotron X-Radiation Anomalous Dispersion Scattering

Mixed 3d metal oxides are some of the most promising water oxidation catalysts (WOCs), but it is very difficult to know the locations and percent occupancies of different 3d metals in these heterogeneous catalysts. Without such information, it is hard to quantify catalysis, stability, and other properties of the WOC as a function of the catalyst active site structure. This study combines the site selective synthesis of a homogeneous WOC with two adjacent 3d metals, [Co₂Ni₂(PW₉O₃₄)₂]^10- (Co₂Ni₂P₂) as a tractable molecular model for CoNi oxide, with the use of multiwavelength synchrotron X-radiation anomalous dispersion scattering (synchrotron XRAS) that quantifies both the location and percent occupancy of Co (∼97% outer-central-belt positions only) and Ni (∼97% inner-central-belt positions only) in Co₂Ni₂P₂. This mixed-3d-metal complex catalyzes water oxidation an order of magnitude faster than its isostructural analogue, [Co₄(PW₉O₃₄)₂]^10- (Co₄P₂). Four independent and complementary lines of evidence confirm that Co₂Ni₂P₂ and Co₄P₂ are the principal WOCs and that Co²⁺(aq) is not. Density functional theory (DFT) studies revealed that Co₄P₂ and Co₂Ni₂P₂ have similar frontier orbitals, while stopped-flow kinetic studies and DFT calculations indicate that water oxidation by both complexes follows analogous multistep mechanisms, including likely Co-OOH formation, with the energetics of most steps being lower for Co₂Ni₂P₂ than for Co₄P₂. Synchrotron XRAS should be generally applicable to active-site-structure-reactivity studies of multi-metal heterogeneous and homogeneous catalysts.

Dilute Alloys Based on Au, Ag, or Cu for Efficient Catalysis: From Synthesis to Active Sites

The development of new catalyst materials for energy-efficient chemical synthesis is critical as over 80% of industrial processes rely on catalysts, with many of the most energy-intensive processes specifically using heterogeneous catalysis. Catalytic performance is a complex interplay of phenomena involving temperature, pressure, gas composition, surface composition, and structure over multiple length and time scales. In response to this complexity, the integrated approach to heterogeneous dilute alloy catalysis reviewed here brings together materials synthesis, mechanistic surface chemistry, reaction kinetics, in situ and operando characterization, and theoretical calculations in a coordinated effort to develop design principles to predict and improve catalytic selectivity. Dilute alloy catalysts─in which isolated atoms or small ensembles of the minority metal on the host metal lead to enhanced reactivity while retaining selectivity─are particularly promising as selective catalysts. Several dilute alloy materials using Au, Ag, and Cu as the majority host element, including more recently introduced support-free nanoporous metals and oxide-supported nanoparticle "raspberry colloid templated (RCT)" materials, are reviewed for selective oxidation and hydrogenation reactions. Progress in understanding how such dilute alloy catalysts can be used to enhance selectivity of key synthetic reactions is reviewed, including quantitative scaling from model studies to catalytic conditions. The dynamic evolution of catalyst structure and composition studied in surface science and catalytic conditions and their relationship to catalytic function are also discussed, followed by advanced characterization and theoretical modeling that have been developed to determine the distribution of minority metal atoms at or near the surface. The integrated approach demonstrates the success of bridging the divide between fundamental knowledge and design of catalytic processes in complex catalytic systems, which can accelerate the development of new and efficient catalytic processes.

Selective hydrogenation of succinic acid to gamma-butyrolactone with PVP-capped CuPd catalysts

A reusable catalyst with a low metal loading amount of PVP-capped Pd rich CuPd nanoparticles was explored for highly selective production of γ-butyrolactone via hydrogenation of succinic acid at mild hydrogen pressure.

XAS Data Preprocessing of Nanocatalysts for Machine Learning Applications

Innovative development in the energy and chemical industries is mainly dependent on advances in the accelerated design and development of new functional materials. The success of research in new nanocatalysts mainly relies on modern techniques and approaches for their precise characterization. The existing methods of experimental characterization of nanocatalysts, which make it possible to assess the possibility of using these materials in specific chemical reactions or applications, generate significant amounts of heterogeneous data. The acceleration of new functional materials, including nanocatalysts, directly depends on the speed and quality of extracting hidden dependencies and knowledge from the obtained experimental data. Usually, such experiments involve different characterization techniques and different types of X-ray absorption spectroscopy (XAS) too. Using the machine learning (ML) methods based on XAS data, we can study and predict the atomic-scale structure and another bunch of parameters for the nanocatalyst efficiently. However, before using any ML model, it is necessary to make sure that the XAS raw experimental data is properly pre-processed, cleared, and prepared for ML application. Usually, the XAS preprocessing stage is vaguely presented in scientific studies, and the main efforts of researchers are devoted to the ML description and implementation stage. However, the quality of the input data influences the quality of ML analysis and the prediction results used in the future. This paper fills the gap between the stage of obtaining XAS data from synchrotron facilities and the stage of using and customizing various ML analysis and prediction models. We aimed this study to develop automated tools for the preprocessing and presentation of data from physical experiments and the creation of deposited datasets on the basis of the example of studying palladium-based nanocatalysts using synchrotron radiation facilities. During the study, methods of preliminary processing of XAS data were considered, which can be conditionally divided into X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). This paper proposes a software toolkit that implements data preprocessing scenarios in the form of a single pipeline. The main preprocessing methods used in this study proposed are principal component analysis (PCA); z-score normalization; the interquartile method for eliminating outliers in the data; as well as the k-means machine learning method, which makes it possible to clarify the phase of the studied material sample by clustering feature vectors of experiments. Among the results of this study, one should also highlight the obtained deposited datasets of physical experiments on palladium-based nanocatalysts using synchrotron radiation. This will allow for further high-quality data mining to extract new knowledge about materials using artificial intelligence methods and machine learning models, and will ensure the smooth dissemination of these datasets to researchers and their reuse.

Assessing the Catalytic Behavior of Platinum Group Metal-Based Ultrathin Nanowires Using X-ray Absorption Spectroscopy

Ultrathin metal-based nanowires have excelled as electrocatalysts in small-molecule reactions, such as the oxygen reduction reaction (ORR), the methanol oxidation reaction (MOR), and the ethanol oxidation reaction (EOR), and have consistently outperformed analogous Pt/C standards. As such, a detailed understanding of the structural and electronic properties of ultrathin nanowires is essential in terms of understanding structure-property correlations, which are crucial in the rational design of ever more sophisticated electrocatalysts. X-ray absorption spectroscopy (XAS) represents an important and promising characterization technique with which to acquire unique insights into the electronic structure and the local atomic structure of nanomaterials. Herein, we discuss tangible examples of how both ex situ and in situ XAS experiments have been recently applied to probing the complex behavior of ultrathin nanowires used in electrocatalysis. Moreover, based on this precedence, we provide ideas about the future potential and direction of these ongoing efforts.

A simple method for mitigating error in the fixed-offset of a double-crystal monochromator

In order to maintain a constant monochromatic synchrotron X-ray beam height for all energies, the separation between the crystals of a double-crystal monochromator is typically adjusted, via translation of the second crystal, while X-ray energy is varied, via rotation of the crystal pair. The ability to accurately translate the second crystal requires precise knowledge of the separation between the two crystals and, when present, crystal miscuts. Here, a simple method for calibrating the crystal gap from measured variation in the X-ray beam height that eliminates error in the fixed beam offset is provided.

Atomic-Scale Tailoring and Molecular-Level Tracking of Oxygen-Containing Tungsten Single-Atom Catalysts with Enhanced Singlet Oxygen Generation

The local coordination structure of metal atoms in single-atom catalysts (SACs) greatly influences their catalytic performance. And for most SACs, single metal atoms were anchored on carbon materials with N or C coordination. However, the rational design of oxygen-containing SACs and analyzing its structure-performance relationship remain challenging. Herein, we used amino-rich compounds to tailor the metatungstate and fix the W atoms and finally obtained the oxygen-containing W-SACs. The structural evolution of tungsten and its coordination atoms were tracked by electrospray ionization high-definition mass spectrometry. Furthermore, aberration-corrected transmission electron microscopy, X-ray absorption fine-structure spectroscopy, and first-principles calculation results revealed that different from the traditional SACs, the WO₂N₂ moiety (W coordinated with two O atoms and two N atoms) may be the favored structure for W species. This special structure promoted the energy transfer for enhancing singlet oxygen generation. This work presents an efficient way to prepare more high-efficiency SACs by atomic-scale tailoring and structural evolution tracking at the molecular level.

The Influence of Size, Shape, and Twin Boundaries on Heat-Induced Alloying in Individual Au@Ag Core-Shell Nanoparticles

Environmental conditions during real-world application of bimetallic core-shell nanoparticles (NPs) often include the use of elevated temperatures, which are known to cause elemental redistribution, in turn significantly altering the properties of these nanomaterials. Therefore, a thorough understanding of such processes is of great importance. The recently developed combination of fast electron tomography with in situ heating holders is a powerful approach to investigate heat-induced processes at the single NP level, with high spatial resolution in 3D. In combination with 3D finite-difference diffusion simulations, this method can be used to disclose the influence of various NP parameters on the diffusion dynamics in Au@Ag core-shell systems. A detailed study of the influence of heating on atomic diffusion and alloying for Au@Ag NPs with varying core morphology and crystallographic details is carried out. Whereas the core shape and aspect ratio of the NPs play a minor role, twin boundaries are found to have a strong influence on the elemental diffusion.

Insights into Nucleation and Growth of Colloidal Quaternary Nanocrystals by Multimodal X-ray Analysis

Copper chalcogenide nanocrystals find applications in photovoltaic inks, bio labels, and thermoelectric materials. We reveal insights in the nucleation and growth during synthesis of anisotropic Cu2ZnSnS4 nanocrystals by simultaneously performing in situ X-ray absorption spectroscopy (XAS) and small-angle X-ray scattering (SAXS). Real-time XAFS reveals that upon thiol injection into the reaction flask, a key copper thiolate intermediate species is formed within fractions of seconds, which decomposes further within a narrow temperature and time window to form copper sulfide nanocrystals. These nanocrystals convert into Cu2ZnSnS4 nanorods by sequentially incorporating Sn and Zn. Real-time SAXS and ex situ TEM of aliquots corroborate these findings. Our work demonstrates how combined in situ X-ray absorption and small-angle X-ray scattering enables the understanding of mechanistic pathways in colloidal nanocrystal formation.

Reconciling structure prediction of alloyed, ultrathin nanowires with spectroscopy

A number of complementary, synergistic advances are reported herein. First, we describe the 'first-time' synthesis of ultrathin Ru2Co1 nanowires (NWs) possessing average diameters of 2.3 ± 0.5 nm using a modified surfactant-mediated protocol. Second, we utilize a combination of quantitative EDS, EDS mapping (along with accompanying line-scan profiles), and EXAFS spectroscopy results to probe the local atomic structure of not only novel Ru2Co1 NWs but also 'control' samples of analogous ultrathin Ru1Pt1, Au1Ag1, Pd1Pt1, and Pd1Pt9 NWs. We demonstrate that ultrathin NWs possess an atomic-level geometry that is fundamentally dependent upon their intrinsic chemical composition. In the case of the PdPt NW series, EDS mapping data are consistent with the formation of a homogeneous alloy, a finding further corroborated by EXAFS analysis. By contrast, EXAFS analysis results for both Ru1Pt1 and Ru2Co1 imply the generation of homophilic structures in which there is a strong tendency for the clustering of 'like' atoms; associated EDS results for Ru1Pt1 convey the same conclusion, namely the production of a heterogeneous structure. Conversely, EDS mapping data for Ru2Co1 suggests a uniform distribution of both elements. In the singular case of Au1Ag1, EDS mapping results are suggestive of a homogeneous alloy, whereas EXAFS analysis pointed to Ag segregation at the surface and an Au-rich core, within the context of a core-shell structure. These cumulative outcomes indicate that only a combined consideration of both EDS and EXAFS results can provide for an accurate representation of the local atomic structure of ultrathin NW motifs.

In Situ/Operando Electrocatalyst Characterization by X-ray Absorption Spectroscopy

During the last decades, X-ray absorption spectroscopy (XAS) has become an indispensable method for probing the structure and composition of heterogeneous catalysts, revealing the nature of the active sites and establishing links between structural motifs in a catalyst, local electronic structure, and catalytic properties. Here we discuss the fundamental principles of the XAS method and describe the progress in the instrumentation and data analysis approaches undertaken for deciphering X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra. Recent usages of XAS in the field of heterogeneous catalysis, with emphasis on examples concerning electrocatalysis, will be presented. The latter is a rapidly developing field with immense industrial applications but also unique challenges in terms of the experimental characterization restrictions and advanced modeling approaches required. This review will highlight the new insight that can be gained with XAS on complex real-world electrocatalysts including their working mechanisms and the dynamic processes taking place in the course of a chemical reaction. More specifically, we will discuss applications of in situ and operando XAS to probe the catalyst's interactions with the environment (support, electrolyte, ligands, adsorbates, reaction products, and intermediates) and its structural, chemical, and electronic transformations as it adapts to the reaction conditions.

Remote controlled optical manipulation of bimetallic nanoparticle catalysts using peptides

Remote optical manipulation of peptide ligands on bimetallic nanoparticle surfaces allows for tunable catalytic reactivity.

Operando NRIXS and XAFS Investigation of Segregation Phenomena in Fe-Cu and Fe-Ag Nanoparticle Catalysts during CO2 Electroreduction

Operando nuclear resonant inelastic X‐ray scattering (NRIXS) and X‐ray absorption fine‐structure spectroscopy (XAFS) measurements were used to gain insight into the structure and surface composition of FeCu and FeAg nanoparticles (NPs) during the electrochemical CO₂ reduction (CO₂RR) and to extract correlations with their catalytic activity and selectivity. The formation of a core–shell structure during CO₂RR for FeAg NPs was inferred from the analysis of the operando NRIXS data (phonon density of states, PDOS) and XAFS measurements. Electrochemical analysis of the FeAg NPs revealed a faradaic selectivity of 36 % for CO in 0.1 M KHCO₃ at −1.1 V vs. RHE, similar to that of pure Ag NPs. In contrast, a predominant selectivity towards H₂ evolution is obtained in the case of the FeCu NPs, analogous to the results obtained for pure Fe NPs, although small Cu NPs have also been shown to favor H₂ production.

Feasibility of Laboratory-Based EXAFS Spectroscopy with Cryogenic Detectors

Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy is a powerful technique that gives element-specific information about the structure of molecules. The development of a laboratory EXAFS spectrometer capable of measuring transmission spectra would be a significant advance as the technique is currently only available at synchrotron radiation lightsources. Here, we explore the potential of cryogenic detectors as the energy resolving component of a laboratory transmission EXAFS instrument. We examine the energy resolution, count-rate, and detector stability needed for good EXAFS spectra and compare these to the properties of cryogenic detectors and conventional X-ray optics. We find that superconducting tunnel junction (STJ) detectors are well-suited for this application.