Construction of Single-Crystalline Hierarchical ZSM-5 with Open Nanoarchitectures via Anisotropic-Kinetics Transformation for the Methanol-to-Hydrocarbons Reaction

We report an anisotropic-kinetics transformation strategy to prepare single-crystalline aluminosilicate MFI zeolites (ZSM-5) with highly open nanoarchitectures and hierarchical porosities. The methodology relies on the cooperative effect of in situ etching and recrystallization on the evolution of pure-silica MFI zeolite (silicalite-1) nanotemplates under hydrothermal conditions. The strategy enables a controllable preparation of ZSM-5 nanostructures with diverse open geometries by tuning the relative rate difference between etching and recrystallization processes. Meanwhile, it can also be extended to synthesize other heteroatom-substituted MFI zeolite nanocages. Compared with conventional ZSM-5 microcrystals, nanocrystals, and nanoboxes, the ZSM-5 nanocages with single-crystalline nature, highly open nanoarchitectures, and hierarchical porosities exhibit remarkably enhanced catalytic lifetime and low coking rate in the methanol-to-hydrocarbons (MTH) reaction.

Engineering a local acid-like environment in alkaline medium for efficient hydrogen evolution reaction

Tuning the local reaction environment is an important and challenging issue for determining electrochemical performances. Herein, we propose a strategy of intentionally engineering the local reaction environment to yield highly active catalysts. Taking Pt^δ− nanoparticles supported on oxygen vacancy enriched MgO nanosheets as a prototypical example, we have successfully created a local acid-like environment in the alkaline medium and achieve excellent hydrogen evolution reaction performances. The local acid-like environment is evidenced by operando Raman, synchrotron radiation infrared and X-ray absorption spectroscopy that observes a key H₃O⁺ intermediate emergence on the surface of MgO and accumulation around Pt^δ− sites during electrocatalysis. Further analysis confirms that the critical factors of the forming the local acid-like environment include: the oxygen vacancy enriched MgO facilitates H₂O dissociation to generate H₃O⁺ species; the F centers of MgO transfers its unpaired electrons to Pt, leading to the formation of electron-enriched Pt^δ− species; positively charged H₃O⁺ migrates to negatively charged Pt^δ− and accumulates around Pt^δ− nanoparticles due to the electrostatic attraction, thus creating a local acidic environment in the alkaline medium.

While catalysts have intrinsic activities toward reactions, such performances often require further optimization. Here, authors engineer an acid-like environment in alkaline media by fine-tuning the reaction environment of platinum nanoparticles on oxide nanosheets for H₂ evolution electrocatalysis.

Mesoporous PdBi nanocages for enhanced electrocatalytic performances by all-direction accessibility and steric site activation

An effective yet simple approach was developed to synthesize mesoporous PdBi nanocages for electrochemical applications. This technique relies on the subtle utilization of the hydrolysis of a metal salt to generate precipitate cores in situ as templates for navigating the growth of mesoporous shells with the assistance of polymeric micelles. The mesoporous PdBi nanocages are then obtained by excavating vulnerable cores and regulating the crystals of mesoporous metallic skeletons. The resultant mesoporous PdBi nanocages exhibited excellent electrocatalytic performance toward the ethanol oxidation reaction with a mass activity of 3.56 A mg-1_Pd, specific activity of 17.82 mA cm-2 and faradaic efficiency of up to 55.69% for C1 products.

Epitaxial Growth of Ultrathin Highly Crystalline Pt-Ni Nanostructure on a Metal Carbide Template for Efficient Oxygen Reduction Reaction

Structure engineering strategies such as core-shell and hollow nanostructures are effective pathways to improve the utilization of noble metals for catalysis. However, nowadays materials design based on these strategies still largely rely on precious metal templates. Herein, the epitaxial growth of highly crystalline Pt₃ Ni overlayer on earth-abundant nickel carbide is reported, forming Ni₃ C@Pt₃ Ni core-shell nanoparticles with a well-defined interface through a new lattice-match-directed synthetic strategy. Derived from such core-shell nanostructures, ultrathin highly crystalline Pt₃ Ni nanocages have an advantageous configuration of oxygen reduction reaction (ORR)-favored facets and inherently high active surface area for the ORR, bringing high mass activity and specific activity as much as 4.71 A mg_Pt ^-1 and 5.14 mA cm^-2 , which are 26 and 20 times to that of commercial Pt/C, respectively. This novel epitaxial growth of platinum opens up new avenues to rationally design highly active and economical electrocatalysts.

Encapsulating Electron-Rich Pd NPs with Lewis Acidic MOF: Reconciling the Electron-Preference Conflict of the Catalyst for Cascade Condensation via Nitro Reduction

Cascade reactions take advantage of step-saving and facile operation for obtaining chemicals. Herein, catalytic hydrogenation of nitroarene coupled condensation with β-diketone to afford β-ketoenamines is achieved by an integrated nanocatalyst, Pd-e@UiO-66. The catalyst has the structure of an acid-rich metal-organic framework (MOF), UiO-66-encapsulated electron-rich Pd nanoparticles, and it reconciles the electron-effect contradiction of cascade catalytic reactions: catalytic hydrogenation requires an electron-rich catalyst, while condensation requires electron-deficient Lewis acid sites. The catalyst showed good activity, high chemoselectivity, and universal applicability for the synthesis of β-ketoenamines using nitroarenes. More than 30 β-ketoenamines have been successfully prepared with up to 99% yield via the methodology of relay catalysis. The catalyst exhibited excellent stability to maintain its catalytic performance for more than five cycles. Furthermore, we conducted an in-depth exploration of the reaction mechanism with theoretical calculations.

PdPtRu nanocages with tunable compositions for boosting the methanol oxidation reaction

PtRu/C is a well-known commercial electrocatalyst with promising performance for the methanol oxidation reaction (MOR). Further improving the MOR properties of PtRu-based electrocatalysts is highly desirable, especially through structure design. Here we report a facile approach for the synthesis of PdPtRu nanocages with different components through a seed-mediated approach followed by chemical etching. The Pd@PtRu nanocubes were first generated using Pd nanocubes as the seeds and some Pd atoms were subsequently etched away, leading to the nanocages. When evaluated as electrocatalysts for the MOR in acidic media, the PdPtRu nanocages exhibited substantially enhanced catalytic activity and stability relative to commercial Pt/C and PtRu/C. Specifically, PdPt_2.5Ru_2.4 achieved the highest specific (8.2 mA cm^-2) and mass (0.75 mA mg_Pt ^-1) activities for the MOR, which are 2.2 and 4.2 times higher than those of commercial Pt/C. Such an enhancement can be attributed to the highly open structure of the nanocages, and the possible synergistic effect between the three components.

Operando Imaging of Ce Radical Scavengers in a Practical Polymer Electrolyte Fuel Cell by 3D Fluorescence CT-XAFS and Depth-Profiling Nano-XAFS-SEM/EDS Techniques

There is little information on the spatial distribution, migration, and valence of Ce species doped as an efficient radical scavenger in a practical polymer electrolyte fuel cell (PEFC) for commercial fuel cell vehicles (FCVs) closely related to a severe reliability issue for long-term PEFC operation. An in situ three-dimensional fluorescence computed tomography-X-ray absorption fine structure (CT-XAFS) imaging technique and an in situ same-view nano-XAFS-scanning electron microscopy (SEM)/energy-dispersive spectrometry (EDS) combination technique were applied for the first time to perform operando spatial visualization and depth-profiling analysis of Ce radical scavengers in a practical PEFC of Toyota MIRAI FCV under PEFC operating conditions. Using these in situ techniques, we successfully visualized and analyzed the domain, density, valence, and migration of Ce scavengers that were heterogeneously distributed in the components of PEFC, such as anode microporous layer, anode catalyst layer, polymer electrolyte membrane (PEM), cathode catalyst layer, and cathode microporous layer. The average Ce valence states in the whole PEFC and PEM were 3.9+ and 3.4+, respectively, and the Ce³⁺/Ce⁴⁺ ratios in the PEM under H₂ (anode)-N₂ (cathode) at an open-circuit voltage (OCV), H₂-air at 0.2 A cm^-2, and H₂-air at 0.0 A cm^-2 were 70 ± 5:30 ± 5%, as estimated by both in situ fluorescence CT-X-ray absorption near-edge spectroscopy (XANES) and nano-XANES-SEM/EDS techniques. The Ce³⁺ migration rates in the electrolyte membrane toward the anode and cathode electrodes ranged from 0.3 to 3.8 μm h^-1, depending on the PEFC operating conditions. Faster Ce³⁺ migration was not observed with voltage transient response processes by highly time-resolved (100 ms) and spatially resolved (200 nm) nano-XANES imaging. Ce³⁺ ions were suggested to be coordinated with both Nafion sulfonate (Nf_sul) groups and water to form [Ce(Nf_sul)_x(H₂O)_y]³⁺. The Ce migration behavior may also be affected by the spatial density of Ce, interactions of Ce with Nafion, thickness and states of the PEM, and H₂O convection, in addition to the PEFC operating conditions. The unprecedented operando imaging of Ce radical scavengers in the practical PEFCs by both in situ three-dimensional (3D) fluorescence CT-XAFS imaging and in situ depth-profiling nano-XAFS-SEM/EDS techniques yields intriguing insights into the spatial distribution, chemical states, and behavior of Ce scavengers under the working conditions for the development of next-generation PEFCs with high long-term reliability and durability.

Stabilization of Exposed Metal Nanocrystals in High-Temperature Heterogeneous Catalysis

Colloidal metal nanocrystals with uniform sizes, shapes, compositions, and architectures are ideal building blocks for constructing heterogeneous catalysts with well-defined characteristics toward the investigation of accurate structure-property relationships and better understanding of catalytic mechanism. However, their applications in high-temperature heterogeneous catalysis are often restricted by the difficulty in maintaining the high metal dispersity and easy accessibility to active sites under harsh operating conditions. Here, a partial-oxide-coating strategy is proposed to stabilize metal nanocrystals against sintering and meanwhile enable an effective exposure of active sites. As a proof-of-concept, controlled partial silica coating of colloidally prepared Pd_0.82 Ni_0.18 nanocrystals with the size of 8 nm is demonstrated. This partially coated catalyst exhibits excellent activity, selectivity, and stability, outperforming its counterparts with fully coated and supported structures, in reverse water gas shift (RWGS) catalysis particularly at high operating temperatures. This study opens a new avenue for the exploration of colloidal metal nanocrystals in high-temperature heterogeneous catalysis.

Highly efficient catalytic reduction of 4-nitrophenol and organic dyes by ultrafine palladium nanoparticles anchored on CeO2 nanorods

Uniformly dispersed Pd nanoparticles on certain supports exhibit exceptional catalytic performance toward various environmental applications. In this work, ultrafine Pd nanoparticles anchored on CeO₂ nanorods were synthesized via an absorption-in situ reduction method. The activity of the CeO₂/Pd nanocomposites was systematically investigated toward reduction of 4-nitrophenol (4-NP) and organic dyes including methyl blue, rhodamine B, methyl orange, and Congo red. The results indicated that the CeO₂/Pd nanocomposites with different weight ratios of Pd nanoparticles (10.23 wt%, 11.01 wt%, and 14.27 wt%) can almost completely reduce 4-NP with a rate constant of 3.31×10^-1, 3.22×10^-1, and 2.23×10^-1 min^-1. Besides, the 10.23 wt% CeO₂/Pd nanocomposites exhibit remarkable enhanced catalytic activity toward reduction of organic dyes. The catalysts display ideal stability after being used for three times for the reduction of 4-NP. We believe that our strategy demonstrated here offers insights into the design and fabrication of novel Pd-based nanocomposites for various heterogeneous catalysis applications.

Noble Metal-Based Multimetallic Nanoparticles for Electrocatalytic Applications

Noble metal-based multimetallic nanoparticles (NMMNs) have attracted great attention for their multifunctional and synergistic effects, which offer numerous catalytic applications. Combined experimental and theoretical studies have enabled formulation of various design principles for tuning the electrocatalytic performance through controlling size, composition, morphology, and crystal structure of the nanoparticles. Despite significant advancements in the field, the chemical synthesis of NMMNs with ideal characteristics for catalysis, including high activity, stability, product-selectivity, and scalability is still challenging. This review provides an overview on structure-based classification and the general synthesis of NMMN electrocatalysts. Furthermore, postsynthetic treatments, such as the removal of surfactants to optimize the activity, and utilization of NMMNs onto suitable support for practical electrocatalytic applications are highlighted. In the end, future direction and challenges associated with the electrocatalysis of NMMNs are covered.

Understanding the morphology evolution of 1D BiVO4 nanoarrays from nanorods to nanocones with enhanced photocatalytic performance

The controllable synthesis of BiVO4 nanocone and nanorod arrays is reported. The morphology transformation of BiVO4 nanoarrays is accompanied with growth mechanism transformation and the tip structure results in superior photocatalytic performance.

Improving the intrinsic activity of electrocatalysts for sustainable energy conversion: where are we and where can we go?

As we are in the midst of a climate crisis, there is an urgent need to transition to the sustainable production of fuels and chemicals. A promising strategy towards this transition is to use renewable energy for the electrochemical conversion of abundant molecules present in the earth's atmosphere such as H₂O, O₂, N₂ and CO₂, to synthetic fuels and chemicals. A cornerstone to this strategy is the development of earth abundant electrocatalysts with high intrinsic activity towards the desired products. In this perspective, we discuss the importance and challenges involved in the estimation of intrinsic activity both from the experimental and theoretical front. Through a thorough analysis of published data, we find that only modest improvements in intrinsic activity of electrocatalysts have been achieved in the past two decades which necessitates the need for a paradigm shift in electrocatalyst design. To this end, we highlight opportunities offered by tuning three components of the electrochemical environment: cations, buffering anions and the electrolyte pH. These components can significantly alter catalytic activity as demonstrated using several examples, and bring us a step closer towards complete system level optimization of electrochemical routes to sustainable energy conversion.

Recent Advances in Electrocatalysts for Proton Exchange Membrane Fuel Cells and Alkaline Membrane Fuel Cells

The rapid progress of proton exchange membrane fuel cells (PEMFCs) and alkaline exchange membrane fuel cells (AMFCs) has boosted the hydrogen economy concept via diverse energy applications in the past decades. For a holistic understanding of the development status of PEMFCs and AMFCs, recent advancements in electrocatalyst design and catalyst layer optimization, along with cell performance in terms of activity and durability in PEMFCs and AMFCs, are summarized here. The activity, stability, and fuel cell performance of different types of electrocatalysts for both oxygen reduction reaction and hydrogen oxidation reaction are discussed and compared. Research directions on the further development of active, stable, and low-cost electrocatalysts to meet the ultimate commercialization of PEMFCs and AMFCs are also discussed.

Construction of Lattice Strain in Bimetallic Nanostructures and Its Effectiveness in Electrochemical Applications

Bimetallic nanocrystals (NCs), associated with various surface functions such as ligand effect, ensemble effect, and strain effect, exhibit superior electrocatalytic properties. The stress-induced surface strain effect can alter binding strength between the surface active sites and reactants as well as their intermediates, and the electrochemical performance of bimetallic NCs can be significantly facilitated by the lattice-strain modification via their morphologies, sizes, shell-thickness, surface defectiveness as well as compositions. In this review, an overview of fundamental principles, characterization techniques, and quantitative determination of the surface lattice strain is provided. Various strategies and synthesis efforts on creating lattice-strain-engineered bimetallic NCs, including the de-alloying process, atomic layer-by-layer deposition, thermal treatment evolution, one-pot synthesis, and other efforts are also discussed. It is further outlined how the lattice strain effect promotes electrochemical catalysis through the selected case studies. The reactions on oxygen reduction reaction, small molecular oxidation, water splitting reaction, and electrochemical carbon dioxide reduction reactions are focused. In particular, studies of lattice strain arisen from core-shell nanostructure and defectiveness are highlighted. Lastly, the potential challenges are summarized and the prospects of lattice-strain-based engineering on bimetallic nanocatalysts with suggestion and guidance of the future electrocatalyst design are envisioned.

Differences in the Electrochemical Performance of Pt-Based Catalysts Used for Polymer Electrolyte Membrane Fuel Cells in Liquid Half- and Full-Cells

A substantial amount of research effort has been directed toward the development of Pt-based catalysts with higher performance and durability than conventional polycrystalline Pt nanoparticles to achieve high-power and innovative energy conversion systems. Currently, attention has been paid toward expanding the electrochemically active surface area (ECSA) of catalysts and increase their intrinsic activity in the oxygen reduction reaction (ORR). However, despite innumerable efforts having been carried out to explore this possibility, most of these achievements have focused on the rotating disk electrode (RDE) in half-cells, and relatively few results have been adaptable to membrane electrode assemblies (MEAs) in full-cells, which is the actual operating condition of fuel cells. Thus, it is uncertain whether these advanced catalysts can be used as a substitute in practical fuel cell applications, and an improvement in the catalytic performance in real-life fuel cells is still necessary. Therefore, from a more practical and industrial point of view, the goal of this review is to compare the ORR catalyst performance and durability in half- and full-cells, providing a differentiated approach to the durability concerns in half- and full-cells, and share new perspectives for strategic designs used to induce additional performance in full-cell devices.

Atomic-Scale Design of High-Performance Pt-Based Electrocatalysts for Oxygen Reduction Reaction

Fuel cells are regarded as one of the most promising energy conversion devices because of their high energy density and zero emission. Development of high-performance Pt-based electrocatalysts for the oxygen reduction reaction (ORR) is vital to the commercial application of these fuel cell devices. Herein, we review the most significant breakthroughs in the development of high-performance Pt-based ORR electrocatalysts in the past decade. Novel and preferred nanostructures, including biaxially strained core-shell nanoplates, ultrafine jagged nanowires, nanocages with subnanometer-thick walls and nanoframes with three-dimensional surfaces, for excellent performance in ORR are emphasized. Important effects of strain, particle proximity, and surface morphology are fully discussed. The remaining changes and prospective research directions are also proposed.

Mastering the surface strain of platinum catalysts for efficient electrocatalysis

Platinum (Pt) has found wide use as an electrocatalyst for sustainable energy conversion systems^1-3. The activity of Pt is controlled by its electronic structure (typically, the d-band centre), which depends sensitively on lattice strain^4,5. This dependence can be exploited for catalyst design^4,6-8, and the use of core-shell structures and elastic substrates has resulted in strain-engineered Pt catalysts with drastically improved electrocatalytic performances^7,9-13. However, it is challenging to map in detail the strain-activity correlations in Pt-catalysed conversions, which can involve a number of distinct processes, and to identify the optimal strain modification for specific reactions. Here we show that when ultrathin Pt shells are deposited on palladium-based nanocubes, expansion and shrinkage of the nanocubes through phosphorization and dephosphorization induces strain in the Pt(100) lattice that can be adjusted from -5.1 per cent to 5.9 per cent. We use this strain control to tune the electrocatalytic activity of the Pt shells over a wide range, finding that the strain-activity correlation for the methanol oxidation reaction and hydrogen evolution reaction follows an M-shaped curve and a volcano-shaped curve, respectively. We anticipate that our approach can be used to screen out lattice strain that will optimize the performance of Pt catalysts-and potentially other metal catalysts-for a wide range of reactions.

Enhanced oxygen reduction and methanol oxidation reaction over self-assembled Pt-M (M = Co, Ni) nanoflowers

Herein, we introduce a facile approach to synthesize a unique class of Pt-M (M = Ni, Co) catalysts with a nanoflower structure for boosting both oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR). By controlling the surface-active agents, we modified the functional groups surrounding the Pt atoms, tuned the alloying of Pt and the transition metals Ni and Co, and prepared two different kinds of nanodendrites. Their successful synthesis depends on the selection and amount of surfactants (hexadecyltrimethylammonium bromide (CTAB), Polyvinylpyrrolidone (PVP)). Besides, by controlling reaction time, we also explored the forming procedures for Pt-Co globularia nanodendrite (Pt-Co GND) and Pt-Ni petalody nanodendrite (Pt-Ni PND). Our investigation highlights the importance of complex nanoarchitecture, which enables surface and interface modification to achieve excellent catalytic performance in fuel cell electrocatalysis. The characterization of the as-prepared catalysts reveals a high electrochemical surface area and mass activity (2041 mAmg_Pt^-1and 950 mAmg_Pt^-1 for Pt-Co GND and Pt-Ni PND, respectively, for ORR). Furthermore, Pt-Co GND showed a high MOR activity, with a mass activity value recorded at 1615 mAmg_Pt^-1 which is far superior to that for Pt/C. Moreover, both catalysts retain high activity after accelerated durability tests (ADTs). The electron transfer number was calculated by performing the rotating ring-disk electrode (RRDE) measurements. Due to abundant active sites of Pt, both Pt-Co GND and Pt-Ni PND exhibit a 4e^- pathway for ORR with electron transfer number of >3.95.

Surface lattice engineering for fine-tuned spatial configuration of nanocrystals

Hybrid nanocrystals combining different properties together are important multifunctional materials that underpin further development in catalysis, energy storage, et al., and they are often constructed using heterogeneous seeded growth. Their spatial configuration (shape, composition, and dimension) is primarily determined by the heterogeneous deposition process which depends on the lattice mismatch between deposited material and seed. Precise control of nanocrystals spatial configuration is crucial to applications, but suffers from the limited tunability of lattice mismatch. Here, we demonstrate that surface lattice engineering can be used to break this bottleneck. Surface lattices of various Au nanocrystal seeds are fine-tuned using this strategy regardless of their shape, size, and crystalline structure, creating adjustable lattice mismatch for subsequent growth of other metals; hence, diverse hybrid nanocrystals with fine-tuned spatial configuration can be synthesized. This study may pave a general approach for rationally designing and constructing target nanocrystals including metal, semiconductor, and oxide.

Hierarchically Fractal PtPdCu Sponges and their Directed Mass- and Electron-Transfer Effects

Fractal Pt-based materials with hierarchical structures and high self-similarity have attracted more and more attention due to their bioinspiring maximum optimization of energy utilization and mass transfer. However, their high-efficiency design of the mass- and electron-transfer still remains to be a great challenge. Herein, fractal PtPdCu hollow sponges (denoted as PtPdCu-HS) facilitating both directed mass- and electron-transfer are presented. Such directed transfer effects greatly promote electrocatalytic activity, regarded as 3.9 times the mass activity, 7.3 times the specific activity, higher poison tolerance, and higher stability than commercial Pt/C for the methanol oxidation reaction (MOR). A new "directed mass- and electron-transfer" concept, characteristics, and mechanism are proposed at the micro/nanoscale to clarify the structural design and functional enhancement of fractal electrocatalyst. This work displays new possibilities for designing novel nanomaterials with high activity and superior stability toward electrocatalysis or other practical applications.

Metal-organic framework based electrode materials for lithium-ion batteries: a review

Metal-organic frameworks (MOFs) with efficient surface and structural properties have risen as a distinctive class of porous materials through the last few decades, which has enabled MOFs to gain attention in a wide range of applications like drug delivery, gas separation and storage, catalysis and sensors. Likewise, they have also emerged as efficient active materials in energy storage devices owing to their remarkable conducting properties. Metal-organic frameworks (MOFs) have garnered great interest in high-energy-density rechargeable batteries and super-capacitors. Herein the study presents their expanding diversity, structures and chemical compositions which can be tuned at the molecular level. It also aims to evaluate their inherently porous framework and how it facilitates electronic and ionic transportation through the charging and discharging cycles of lithium-ion batteries. In this review we have summarized the various synthesis paths to achieve a particular metal-organic framework. This study focuses mainly on the implementation of metal-organic frameworks as efficient anode and cathode materials for lithium-ion batteries (LIBs) with an evaluation of their influence on cyclic stability and discharge capacity. For this purpose, a brief assessment is made of recent developments in metal-organic frameworks as anode or cathode materials for lithium-ion batteries which would provide enlightenment in optimizing the reaction conditions for designing a MOF structure for the battery community and electrochemical energy storage applications.

Design of Highly Durable Core-Shell Catalysts by Controlling Shell Distribution Guided by In-Situ Corrosion Study

Most degradations in electrocatalysis are caused by corrosion in operation, for example the corrosion of the core in a core-shell electrocatalyst during the oxygen reduction reaction (ORR). Herein, according to the in-situ study on nanoscale corrosion kinetics via liquid cell transmission electron microscopy (LC-TEM) in the authors' previous work, they sequentially designed an optimized nanocube with the protection of more layers on the corners by adjusting the Pt atom distribution on corners and terraces. This modified nanocube (MNC) is much more corrosion resistant in the in-situ observation. Furthermore, in the practical electrochemical stability testing, the MNC catalyst also showed the best stability performance with the 0.37% and 9.01% loss in specific and mass activity after 30 000 cycles accelerated durability test (ADT). This work also demonstrates that how an in-situ study can guide the design of desired materials with improved properties and build a bridge between in-situ study and practical application.

Robust O2 Supplementation from a Trimetallic Nanozyme-Based Self-Sufficient Complementary System Synergistically Enhances the Starvation/Photothermal Therapy against Hypoxic Tumors

Much effort has been focused on novel nanomedicine for cancer therapy. However, tumor hypoxia limits the efficacy of various cancer therapeutics. Herein, we constructed a self-sufficient hybrid enzyme-based silk fibroin hydrogel system, consisting of Pt-decorated hollow Ag-Au trimetallic nanocages (HGN@Pt) and glucose oxidase (GOx), to supply O₂ continuously and consume glucose concurrently and, thereby, synergistically enhance the anti-cancer efficacy of a combined starvation and photothermal therapy operating in a hypoxic tumor microenvironment. Thanks to the cooperative effects of the active surface atoms (resulting from the island-like features of the Pt coating), the intrinsically hollow structure, and the strain effect induced by the trimetallic composition, HGN@Pt displayed efficient catalase-like activity. The enhancement in the generation of O₂ through the decomposition of H₂O₂ mediated by the as-designed nanozyme was greater than 400% when compared with that of hollow Ag-Pt bimetallic nanospheres or tiny Pt nanoparticles. Moreover, in the presence of HGN@Pt, significant amounts of O₂ could be generated within a few minutes, even in an acidic buffer solution (pH 5.8-6.5) containing a low concentration of H₂O₂ (100-500 μM). Because HGN@Pt exhibited a strong surface plasmon resonance peak in the near-infrared wavelength range, it could be used as a photothermal agent for hyperthermia therapy. Furthermore, GOx was released gradually from the SF hydrogel into the tumor microenvironment to mediate the depletion of glucose, leading to glucose starvation-induced cancer cell death. Finally, the O₂ supplied by HGN@Pt overcame the hypoxia of the microenvironment and, thereby, promoted the starvation therapeutic effect of the GOx-mediated glucose consumption. Meanwhile, the GOx-produced H₂O₂ from the oxidation of glucose could be used to regenerate O₂ and, thereby, construct a complementary circulatory system. Accordingly, this study presents a self-sufficient hybrid enzyme-based system that synergistically alleviates tumor hypoxia and induces an anti-cancer effect when combined with irradiation of light from a near-infrared laser.

PdNi/Ni Nanotubes Assembled by Mesoporous Nanoparticles for Efficient Alkaline Ethanol Oxidation Reaction

The optimization of structure and composition is essential to improve the performance of catalysts. Herein, mesoporous nanoparticles assembled PdNi/Ni nanotubes (mPdNi/Ni NTs) are successfully fabricated using nickel nanowires as sacrificial template. The combination of nanotubular structure with mesoporous nanoparticle morphology can provide facilitated transfer channels and sufficient active sites, allowing the full contact and reaction between catalysts and reactants. Therefore, the synthesized mPdNi/Ni NTs exhibited superior ethanol oxidation performance to mesoporous Pd nanotubes and commercial Pd black. This study proposes a rational strategy for the development of nanoparticle assembled nanotubes with surface mesoporous morphology, which can greatly improve catalytic performance in various electrocatalytic fields.

Redox Mediated Control of Electrochemical Potential in Liquid Cell Electron Microscopy

Liquid cell electron microscopy enables the study of nanoscale transformations in solvents with high spatial and temporal resolution, but for the technique to achieve its potential requires a new level of control over the reactivity caused by radical generation under electron beam irradiation. An understanding of how to control electron-solvent interactions is needed to further advance the study of structural dynamics for complex materials at the nanoscale. We developed an approach that scavenges radicals with redox species that form well-defined redox couples and control the electrochemical potential in situ. This approach enables the observation of electrochemical structural dynamics at near-atomic resolution with precise control of the liquid environment. Analysis of nanocrystal etching trajectories indicates that this approach can be generalized to several chemical systems. The ability to simultaneously observe heterogeneous reactions at near-atomic resolution and precisely control the electrochemical potential enables the fundamental study of complex nanoscale dynamics with unprecedented detail.

Hydrogen-Intercalation-Induced Lattice Expansion of Pd@Pt Core-Shell Nanoparticles for Highly Efficient Electrocatalytic Alcohol Oxidation

Lattice engineering on specific facets of metal catalysts is critically important not only for the enhancement of their catalytic performance but also for deeply understanding the effect of facet-based lattice engineering on catalytic reactions. Here, we develop a facile two-step method for the lattice expansion on specific facets, i.e., Pt(100) and Pt(111), of Pt catalysts. We first prepare the Pd@Pt core-shell nanoparticles exposed with the Pt(100) and Pt(111) facets, respectively, via the Pd-seeded epitaxial growth, and then convert the Pd core to PdH_0.43 by hydrogen intercalation. The lattice expansion of the Pd core induces the lattice enlargement of the Pt shell, which can significantly promote the alcohol oxidation reaction (AOR) on both Pt(100) and Pt(111) facets. Impressively, Pt mass specific activities of 32.51 A mg_Pt^-1 for methanol oxidation and 14.86 A mg_Pt^-1 for ethanol oxidation, which are 41.15 and 25.19 times those of the commercial Pt/C catalyst, respectively, have been achieved on the Pt(111) facet. Density functional theory (DFT) calculations indicate that the remarkably improved catalytic performance on both the Pt(100) and the Pt(111) facets through lattice expansion arises from the enhanced OH adsorption. This work not only paves the way for lattice engineering on specific facets of nanomaterials to enhance their electrocatalytic activity but also offers a promising strategy toward the rational design and preparation of highly efficient catalysts.

Progress and Perspectives on Covalent-organic Frameworks (COFs) and Composites for Various Energy Applications

Covalent-organic frameworks (COFs), being a new member of the crystalline porous materials family, have emerged as important materials for energy storage/conversion/generation devices. They possess high surface areas, ordered micro/mesopores, designable structures and an ability to precisely control electro-active groups in their pores, which broaden their application window. Thanks to their low weight density, long range crystallinity, reticular nature and tunable synthesis approach towards two and three dimensional (2D and 3D) networks, they have been found suitable for a range of challenging electrochemical applications. Our review focuses on the progress made on the design, synthesis and structure of COFs and their composites for various energy applications, such as metal-ion batteries, supercapacitors, water-splitting and solar cells. Additionally, attempts have been made to correlate the structural and mechanistic characteristics of COFs with their applications.

Understanding of Strain-Induced Electronic Structure Changes in Metal-Based Electrocatalysts: Using Pd@Pt Core-Shell Nanocrystals as an Ideal Platform

While metal-based electrocatalysts have garnered extensive attention owing to the large variety of enzyme-mimic properties, the search for such highly-efficient catalysts still relies on empirical explorations, owing to the lack of predictive indicators as well as the ambiguity of structure-activity relationships. Notably, surface electronic structures play a crucial role in metal-based catalysts yet remain unexplored in enzyme-mimics. Herein, the authors investigate the electronic structure as a possible indicator of electrocatalytic activities of H₂ O₂ decomposition and glucose oxidation using Pd@Pt core-shell nanocrystals as a well-defined platform. The electron densities of the Pd@Pt are modulated with the correlation of strain through precise control of surface orientation and the number of atomic layers. The close relationships between the electrocatalytic activities and the surface charge accumulation are found, in which the increase of the electron accumulation can enhance both the enzyme-mimic activities. As a result, the Pd@Pt_3L icosahedra with compressive strain in Pt shells exhibit the highest electrocatalytic activities for H₂ O₂ decomposition and glucose oxidation. Such systematic and comprehensive study provides the structure-activity relationships and paves a new way for the rational design of metal-based electrocatalysts. Especially, the charge accumulation degrees may serve as a general performance indicator for metal-based catalysts.

Conformation-modulated three-dimensional electrocatalysts for high-performance fuel cell electrodes

Unsupported Pt electrocatalysts demonstrate excellent electrochemical stability when used in polymer electrolyte membrane fuel cells; however, their extreme thinness and low porosity result in insufficient surface area and high mass transfer resistance. Here, we introduce three-dimensionally (3D) customized, multiscale Pt nanoarchitectures (PtNAs) composed of dense and narrow (for sufficient active sites) and sparse (for improved mass transfer) nanoscale building blocks. The 3D-multiscale PtNA fabricated by ultrahigh-resolution nanotransfer printing exhibited excellent performance (45% enhanced maximum power density) and high durability (only 5% loss of surface area for 5000 cycles) compared to commercial Pt/C. We also theoretically elucidate the relationship between the 3D structures and cell performance using computational fluid dynamics. We expect that the structure-controlled 3D electrocatalysts will introduce a new pathway to design and fabricate high-performance electrocatalysts for fuel cells, as well as various electrochemical devices that require the precision engineering of reaction surfaces and mass transfer.

Dual Inorganic Sacrificial Template Synthesis of Hierarchically Porous Carbon with Specific N Sites for Efficient Oxygen Reduction

It is still a challenge to achieve efficiently controlled preparation of functional oxygen reduction reaction (ORR) carbon electrocatalysts with multi-preferred structures (hierarchically porous networks and specific carbon-nitrogen bonds) from carbohydrate-containing small molecules via simple one-step pyrolysis. Based on the step-by-step spontaneous gas-foaming strategy, we successfully prepare 3D hierarchically porous networks with tunable N sites (N_P/N_G ≈ 1:1) by pyrolyzing diverse carbohydrates (glucose, maltose, and cyclodextrin) using nonmetal-metal dual inorganic sacrificial templates. In situ evaporation templates can simplify the procedure of the experiments and avoid the active site loss compared with traditional hard templates. Crucially, dual inorganic sacrificial templates can induce abundant defects and microscopic pore structures (the specific surface area increased from 922.403 to 1898.792 m²·g^-1) and tunable N sites compared with single nonmetal sacrificial templates. The regulatory mechanism of dual inorganic templates on N sites (N_P/N_G ≈ 1:1) is independent of the polymeric state of carbohydrate precursors or even the carbonization condition of the pyrolysis process. A series of carbon materials prepared by this strategy all have ORR-preferred structures and exhibit low ORR overpotentials compared with Pt/C. For instance, the Zn-air battery with βCD-DSC-950-1 exhibits an open-circuit potential of 1.51 V and a peak power density of 180.89 mW·cm^-2, higher than those of Pt/C (1.47 V, 174.94 mW·cm^-2). In general, the conversion of carbohydrate-containing small molecules to functional carbon materials provides a new strategy for the development of carbonaceous electrocatalysts.

Trimetallic synergy in dendritic intermetallic PtSnBi nanoalloys for promoting electrocatalytic alcohol oxidation

Developing effective and robust novel electrocatalysts for direct alcohol fuel cells has been gaining much attention. However, the widely used Pt catalyst suffers from limitations including the sluggish kinetics, severe CO poisoning, and catalyst lost caused by aggregation and Ostwald ripening during alcohol oxidation reaction. Herein, dendritic intermetallic PtSnBi nanoalloys were synthesized via a facile hydrothermal approach with high electrocatalytic performance and enhanced CO resistance for methanol oxidation reaction (MOR) and ethanol oxidation reaction (EOR) owing to the synergism of the chosen three elements and unique three-dimensional morphology. Specifically, the PtSnBi nanoalloys display 4.6 and 6.7 times higher of mass activity (7.02 A mg^-1_Pt) and specific activity (16.65 mA cm^-2) toward MOR than those of commercial Pt/C, respectively. The mass activity of PtSnBi nanoalloys still retains 75.7% of the initial value after 800 cycles of stability test, superior to Pt/C (38.0%). The dual-functional effect of Sn, optimized electronic structure by the ligand effect, and unique atomic arrangement are responsible for the enhanced MOR activity and stability of PtSnBi nanoalloys. Furthermore, the PtSnBi nanoalloys with highlighted anti-CO poisoning capacity also improve the electrocatalytic performance toward EOR, indicating their great promise as broad energy electrocatalysts.

Facile Synthesis of Pd@PtM (M = Rh, Ni, Pd, Cu) Multimetallic Nanorings as Efficient Catalysts for Ethanol Oxidation Reaction

Pt-based multimetallic nanorings with a hollow structure are attractive as advanced catalysts due to their fantastic structure feature. However, the general method for the synthesis of such unique nanostructures is still lack. Here we report the synthesis of Pd@PtM (M = Rh, Ni, Pd, Cu) multimetallic nanorings by selective epitaxial growth of Pt alloyed shells on the periphery of Pd nanoplates in combination with oxidative etching of partial Pd in the interior. In situ generation of CO and benzoic acid arising from interfacial catalytic reactions between Pd nanoplates and benzaldehyde are critical to achieve high-quality Pt-based multimetallic nanorings. Specifically, the in-situ generated CO promotes the formation of Pt alloyed shells and their epitaxial growth on Pd nanoplates. In addition, the as-formed benzoic acid and residual oxygen are responsible for selective oxidative etching of partial Pd in the interior. When evaluated as electrocatalysts, the Pd@PtRh nanorings exhibit remarkably enhanced activity and stability for ethanol oxidation reaction (EOR) compared to the Pd@PtRh nanoplates and commercial Pt/C due to their hollow nanostructures.

Atomistic insights into the nucleation and growth of platinum on palladium nanocrystals

Despite the large number of reports on colloidal nanocrystals, very little is known about the mechanistic details in terms of nucleation and growth at the atomistic level. Taking bimetallic core-shell nanocrystals as an example, here we integrate in situ liquid-cell transmission electron microscopy with first-principles calculations to shed light on the atomistic details involved in the nucleation and growth of Pt on Pd cubic seeds. We elucidate the roles played by key synthesis parameters, including capping agent and precursor concentration, in controlling the nucleation site, diffusion path, and growth pattern of the Pt atoms. When the faces of a cubic seed are capped by Br-, Pt atoms preferentially nucleate from corners and then diffuse to edges and faces for the creation of a uniform shell. The diffusion does not occur until the Pt deposited at the corner has reached a threshold thickness. At a high concentration of the precursor, self-nucleation takes place and the Pt clusters then randomly attach to the surface of a seed for the formation of a non-uniform shell. These atomistic insights offer a general guideline for the rational synthesis of nanocrystals with diverse compositions, structures, shapes, and related properties.

Ultrafine Pt-Ni nanoparticles in hollow porous carbon spheres for remarkable oxygen reduction reaction catalysis

Ultrafine bimetallic Pt-Ni nanoparticles, which catalyze the oxygen reduction reaction (ORR) efficiently, were successfully prepared in hollow porous carbon spheres (HPCSs) under the assistance of organic molecules. 2,2'-Dipyridylamine (dpa) was found to be most effective in preparing homogeneous small Pt-Ni nanoparticles (2.0 ± 0.4 nm) without the phase separation of Pt and Ni during synthesis, and the assistance of the organic molecules was investigated for the alloy nanoparticle formation. The Pt-Ni nanoparticle/HPCS catalyst synthesized in the presence of dpa exhibited remarkable electrochemical performance in the ORR showing a high mass activity of 3.25 ± 0.14 A mg-1Pt at 0.9 VRHE (13.5-fold higher relative to a commercial Pt/C catalyst), a large electrochemical surface area of 105 ± 8 m2 g-1Pt, and high durability. After 60 000 cycles of accelerated durability testing, the mass activity was still 12.3 times higher than that of the commercial Pt/C catalyst.

Ultraprecision Imaging and Manipulation of Plasmonic Nanostructures by Integrated Nanoscopic Correction

Optical manipulation and imaging of nano-objects with nanometer precision is highly desirable for nanomaterial and biological studies due to inherent noninvasiveness. However, time constraints and current segregated experimental systems for nanoimaging and nanomanipulation limits real-time super-resolution imaging with spatially enhanced manipulation. Here, an integrated nanoscopic correction (iNC) method to enable multimodal nanomanipulation-nanoimaging is reported. The iNC consists of a multimodal voltage-tunable power modulator, polarization rotator, and polarizer. Using the iNC, plasmonic nano-objects which are below the diffraction limit and which can be distinguished by direct observation without post processing are demonstrated. Furthermore, such direct observations with enhanced nanometer spatial stability and millisecond high speed are shown. Precise trapping and rapid rotation of gold nanorods with the iNC are demonstrated successfully. With non-invasive post-processing free nanoimaging and nanomanipulation, it is anticipated that the iNC will make contributions in the nanomaterial and biological sciences requiring precision optics.

General Synthesis of Amorphous PdM (M = Cu, Fe, Co, Ni) Alloy Nanowires for Boosting HCOOH Dehydrogenation

Noble metal-based nanomaterials with amorphous structures are promising candidates for developing efficient electrocatalysts. However, their synthesis remains a significant challenge, especially under mild conditions. In this paper, we report a general strategy for preparing amorphous PdM nanowires (a-PdM NWs, M = Fe, Co, Ni, and Cu) at low temperatures by exploiting glassy non-noble metal (M) nuclei generated by special ligand adsorption as the amorphization dictator. When evaluated as electrocatalysts toward formic acid oxidation, a-PdCu NWs can deliver the mass and specific activities as high as 2.93 A/mg_Pd and 5.33 mA/cm², respectively; these are the highest values for PdCu-based catalysts reported thus far, far surpassing the crystalline-dominant counterparts and commercial Pd/C. Theoretical calculations suggest that the outstanding catalytic performance of a-PdCu NWs arises from the amorphization-induced high surface reactivity, which can efficiently activate the chemically stable C-H bond and thereby significantly facilitate the dissociation of HCOOH.

Deposition of Atomically Thin Pt Shells on Amorphous Palladium Phosphide Cores for Enhancing the Electrocatalytic Durability

As an excellent electrocatalyst, platinum (Pt) is often deposited as a thin layer on a nanoscale substrate to achieve high utilization efficiency. However, the practical application of the as-designed catalysts has been substantially restricted by the poor durability arising from the leaching of cores. Herein, by employing amorphous palladium phosphide (a-Pd-P) as substrates, we develop a class of leaching-free, ultrastable core-shell Pt catalysts with well-controlled shell thicknesses and surface structures for fuel cell electrocatalysis. When a submonolayer of Pt is deposited on the 6 nm nanocubes, the resulting Pd@a-Pd-P@Pt_SML core-shell catalyst can deliver a mass activity as high as 4.08 A/mg_Pt and 1.37 A/mg_Pd+Pt toward the oxygen reduction reaction at 0.9 V vs the reversible hydrogen electrode and undergoes 50 000 potential cycles with only ∼9% activity loss and negligible structural deformation. As elucidated by the DFT calculations, the superior durability of the catalysts originates from the high corrosion resistance of the disordered a-Pd-P substrates and the strong interfacial Pt-P interactions between the Pt shell and amorphous Pd-P layer.

Janus Nanocages of Platinum-Group Metals and Their Use as Effective Dual-Electrocatalysts

Janus nanocages with distinctive platinum-group metals on the outer and inner surfaces can naturally catalyze at least two different reactions. Here we report a general method based on successive deposition and then selective etching for the facile synthesis of such nanocages. We have fabricated 11 different types of Janus nanocages characterized by a uniform size and well-defined {100} facets, together with porous, ultrathin, asymmetric walls up to 1.6 nm thick. When tested as dual-electrocatalysts toward oxygen reduction and evolution reactions, the Janus nanocages based on Pt and Ir exhibited superior activities depending on the thickness and relative position of the metal layer. Density functional theory studies suggest that the alloy composition and surface structure of the nanocages both play important roles in enhancing the electrocatalytic activities by modulating the stability of key reaction intermediates.

Recent advances in Pt-based electrocatalysts for PEMFCs

In order to reduce the cost and improve the performance of proton exchange membrane fuel cells (PEMFCs), it is imperative to further enhance the activity and durability of Pt based electrocatalysts for the oxygen reduction reaction (ORR). This article analyzes the latest advances in Pt-based ORR electrocatalysts, including the Pt alloys, Pt–M core–shell structures, particle size effects, support effects, doping in Pt/PtM and post treatment. In addition, the performance of some of the developed novel electrocatalysts in membrane electrode assemblies (MEA) is also included for comparison, as they are rarely available and the superior activity and durability exhibited in RDE frequently doesn't translate into MEA.

In this paper, the latest progress in the design of Pt-based ORR electrocatalysts is reviewed, including the understanding of research progress in the synthesis of high activity and high stability catalysts.

The studies on wet chemical etching via in situ liquid cell TEM

Wet chemical etching is a widely used process to fabricate fascinating nanomaterials, such as nanoparticles with precisely controlled size and shape. Understanding the etching mechanism and kinetic evolution process is crucial for controlling wet chemical etching. The development of in situ liquid cell transmission electron microscopy (LCTEM) enables the study on wet chemical etching with high temporal and spatial resolutions. However, there still lack a detailed literature review on the wet chemical etching studies by in situ LCTEM. In this review, we summarize the studies on wet etching nanoparticles, one-dimensional nanomaterials and nanoribbons by in situ LCTEM, including etching rate, anisotropic etching, morphology evolution process, and etching mechanism. The challenges and opportunities of in situ LCTEM are also discussed.