Engineering the electronic and strained interface for high activity of PdMcore@Ptmonolayer electrocatalysts for oxygen reduction reaction

Alloyed nanoparticles with core-shell structures provide a favorable model to modulate interfacial interaction and surface structures at the atomic level, which is important for designing electrocatalysts with high activity and durability. Herein, core-shell structured Pd₃M@Pt/C nanoparticles with binary PdM alloy cores (M = Fe, Ni, and Co) and a monolayer Pt shell were successfully synthesized with diverse interfaces. Among these, Pd₃Fe@Pt/C exhibited the best oxygen reduction reaction catalytic performance, roughly 5.4 times more than that of the commercial Pt/C catalyst used as reference. The significantly enhanced activity is attributed to the combined effects of strain engineering, interfacial electron transfer, and improved Pt utilization. Density functional theory simulations and extended X-ray absorption fine structure analysis revealed that engineering the alloy core with moderate lattice mismatch and alloy composition (Pd₃Fe) optimizes the surface oxygen adsorption energy, thereby rendering excellent electrocatalytic activity. Future researches may use this study as a guide on the construction of highly effective core-shell electrocatalysts for various energy conversions and other applications.

Platinum Single Atoms Supported on Nanoarray-Structured Nitrogen-Doped Graphite Foil with Enhanced Catalytic Performance for Hydrogen Evolution Reaction

Platinum-based single-atom catalysts (SACs) are among the most promising candidates for the practical applications of electrochemical hydrogen evolution reaction (HER), but their catalytic efficiency remains to be further enhanced. Herein, a well-designed nanoarray-structured nitrogen-doped graphite foil (NNGF) substrate is introduced to support Pt SACs in Pt-N₄ construction (Pt₁/NNGF) for HER. Within NNGF, the constructed nanoarray-structured surficial layer for supporting Pt SACs could enhance the exposure of active sites to the electrolyte and improve the reaction and diffusion kinetics; meanwhile, the retained graphite structures in bulk NNGF provide not only the required electrical conductivity but also the mechanical stability and flexibility. Because of such double-layer structures of NNGF, stable Pt-N₄ construction, and binder-free advantages, the Pt₁/NNGF electrode exhibits a low overpotential of 0.023 V at 10 mA cm^-2 and a small Tafel slope of 29.1 mV dec^-1 as well as an excellent long-term durability.

Catalytic Hydrogen Production from Methane: A Review on Recent Progress and Prospect

Natural gas (Methane) is currently the primary source of catalytic hydrogen production, accounting for three quarters of the annual global dedicated hydrogen production (about 70 M tons). Steam–methane reforming (SMR) is the currently used industrial process for hydrogen production. However, the SMR process suffers with insufficient catalytic activity, low long-term stability, and excessive energy input, mostly due to the handling of large amount of CO2 coproduced. With the demand for anticipated hydrogen production to reach 122.5 M tons in 2024, novel and upgraded catalytic processes are desired for more effective utilization of precious natural resources. In this review, we summarized the major descriptors of catalyst and reaction engineering of the SMR process and compared the SMR process with its derivative technologies, such as dry reforming with CO2 (DRM), partial oxidation with O2, autothermal reforming with H2O and O2. Finally, we discussed the new progresses of methane conversion: direct decomposition to hydrogen and solid carbon and selective oxidation in mild conditions to hydrogen containing liquid organics (i.e., methanol, formic acid, and acetic acid), which serve as alternative hydrogen carriers. We hope this review will help to achieve a whole picture of catalytic hydrogen production from methane.

Gradient-Concentration Design of Stable Core-Shell Nanostructure for Acidic Oxygen Reduction Electrocatalysis

Manipulating the surface structure of electrocatalysts at the atomic level is of primary importance to simultaneously achieve the activity and stability dual-criteria in oxygen reduction reaction (ORR) for proton exchange membrane fuel cells. Here, a durable acidic ORR electrocatalyst with the "defective-armored" structure of Pt shell and Pt-Ni core nanoparticle decorated on graphene (Pt-Ni@Pt_D /G) using a facile and controllable galvanic replacement reaction to generate gradient distribution of Pt-Ni composition from surface to interior, followed by a partial dealloying approach, leaching the minor nickel atoms on the surface to generate defective Pt skeleton shell, is reported. The Pt-Ni@Pt_D /G catalyst shows impressive performance for ORR in acidic (0.1 m HClO₄ ) electrolyte, with a high mass activity of threefold higher than that of Pt/C catalyst owing to the tuned electronic structure of locally concave Pt surface sites through synergetic contributions of Pt-Ni core and defective Pt shell. More importantly, the electrochemically active surface areas still retain 96% after 20 000 potential cycles, attributing to the Pt atomic shell acting as the protective "armor" to prevent interior Ni atoms from further dissolution during the long-term operation.

Heterophase fcc-2H-fcc gold nanorods

The crystal phase-based heterostructures of noble metal nanomaterials are of great research interest for various applications, such as plasmonics and catalysis. However, the synthesis of unusual crystal phases of noble metals still remains a great challenge, making the construction of heterophase noble metal nanostructures difficult. Here, we report a one-pot wet-chemical synthesis of well-defined heterophase fcc-2H-fcc gold nanorods (fcc: face-centred cubic; 2H: hexagonal close-packed with stacking sequence of "AB") at mild conditions. Single particle-level experiments and theoretical investigations reveal that the heterophase gold nanorods demonstrate a distinct optical property compared to that of the conventional fcc gold nanorods. Moreover, the heterophase gold nanorods possess superior electrocatalytic activity for the carbon dioxide reduction reaction over their fcc counterparts under ambient conditions. First-principles calculations suggest that the boosted catalytic performance stems from the energetically favourable adsorption of reaction intermediates, endowed by the unique heterophase characteristic of gold nanorods.

Imaging the kinetics of anisotropic dissolution of bimetallic core-shell nanocubes using graphene liquid cells

Chemical design of multicomponent nanocrystals requires atomic-level understanding of reaction kinetics. Here, we apply single-particle imaging coupled with atomistic simulation to study reaction pathways and rates of Pd@Au and Cu@Au core-shell nanocubes undergoing oxidative dissolution. Quantitative analysis of etching kinetics using in situ transmission electron microscopy (TEM) imaging reveals that the dissolution mechanism changes from predominantly edge-selective to layer-by-layer removal of Au atoms as the reaction progresses. Dissolution of the Au shell slows down when both metals are exposed, which we attribute to galvanic corrosion protection. Morphological transformations are determined by intrinsic anisotropy due to coordination-number-dependent atom removal rates and extrinsic anisotropy induced by the graphene window. Our work demonstrates that bimetallic core-shell nanocrystals are excellent probes for the local physicochemical conditions inside TEM liquid cells. Furthermore, single-particle TEM imaging and atomistic simulation of reaction trajectories can inform future design strategies for compositionally and architecturally sophisticated nanocrystals.

Rational design of multicomponent nanocrystals requires atomic-level understanding of reaction kinetics. Here, the authors apply single-particle liquid-cell electron microscopy imaging coupled with atomistic simulations to understand pathways and rates of bimetallic core-shell nanocubes undergoing oxidative dissolution.

Proton exchange membrane with plasmon-active surface for enhancement of fuel cell effectivity

The action of fuel cells with proton-exchanged membranes (PEMs) requires the implementation of the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR) on the opposite sides of the PEMs. Recently, based on several models of electrochemical reactions a significant decrease in the thermodynamic activation barrier of both reactions under plasmon assistance was reported. In this work, we propose the design of a PEM fuel cell with a plasmon-active catalytic surface providing plasmonic triggering and enhancement of fuel cell efficiency. In particular, we deposited bimetallic (Au@Pt) nanostructures on the PEM surface and integrated them into the fuel cell design. Plasmon excitation occurs on the Au nanostructures under light illumination at the corresponding NIR wavelength, while the Pt shell is responsible for the introduction of catalytic sites. Light illumination results in a significant enhancement of the electric current produced by the fuel cell. In particular, the electric current increased several times. Control experiments indicated that the observed enhancement takes place only when the light wavelength is in compliance with the plasmon absorption band and the contribution from thermal effects is negligible. The present approach for the introduction of plasmon assistance into the design of advanced fuel cells makes them suitable for increasing the fuel cell efficiency under sunlight.

Feed gas exchange (startup/shutdown) effects on Pt/C cathode electrocatalysis and surface Pt-oxide behavior in polymer electrolyte fuel cells as revealed using in situ real-time XAFS and high-resolution STEM measurements

The synchronizing measurements of both cyclic voltammograms (CVs) and real-time quick XAFSs (QXAFSs) for Pt/C cathode electrocatalysts in a membrane electrode assembly (MEA) of polymer electrolyte fuel cells (PEFCs) treated by anode-gas exchange (AGEX) and cathode-gas exchange (CGEX) cycles (startup/shutdown conditions of FC vehicles) were performed for the first time to understand the opposite effects of the AGEX and CGEX treatments on the Pt/C performance and durability and also the contradiction between the electrochemical active surface area (ECSA) decrease and the performance increase by CGEX treatment. While the AGEX treatment decreased both the ECSA and performance of MEA Pt/C due to carbon corrosion, it was found that the CGEX treatment decreased the ECSA but increased the Pt/C performance significantly due to high-index (331) facet formation (high-resolution STEM) and hence the suppression of strongly bound Pt-oxide formation at cathode Pt nanoparticle surfaces. Transient QXAFS time-profile analysis for the MEA Pt/C also revealed a direct relationship between the electrochemical performance or durability and transient kinetics of the Pt/C cathode.

Nanocatalosomes as Plasmonic Bilayer Shells with Interlayer Catalytic Nanospaces for Solar-Light-Induced Reactions

Interest and challenges remain in designing and synthesizing catalysts with nature-like complexity at few-nm scale to harness unprecedented functionalities by using sustainable solar light. We introduce "nanocatalosomes"-a bio-inspired bilayer-vesicular design of nanoreactor with metallic bilayer shell-in-shell structure, having numerous controllable confined cavities within few-nm interlayer space, customizable with different noble metals. The intershell-confined plasmonically coupled hot-nanospaces within the few-nm cavities play a pivotal role in harnessing catalytic effects for various organic transformations, as demonstrated by "acceptorless dehydrogenation", "Suzuki-Miyaura cross-coupling" and "alkynyl annulation" affording clean conversions and turnover frequencies (TOFs) at least one order of magnitude higher than state-of-the-art Au-nanorod-based plasmonic catalysts. This work paves the way towards next-generation nanoreactors for chemical transformations with solar energy.

Engineering bunched Pt-Ni alloy nanocages for efficient oxygen reduction in practical fuel cells

Development of efficient and robust electrocatalysts is critical for practical fuel cells. We report one-dimensional bunched platinum-nickel (Pt-Ni) alloy nanocages with a Pt-skin structure for the oxygen reduction reaction that display high mass activity (3.52 amperes per milligram platinum) and specific activity (5.16 milliamperes per square centimeter platinum), or nearly 17 and 14 times higher as compared with a commercial platinum on carbon (Pt/C) catalyst. The catalyst exhibits high stability with negligible activity decay after 50,000 cycles. Both the experimental results and theoretical calculations reveal the existence of fewer strongly bonded platinum-oxygen (Pt-O) sites induced by the strain and ligand effects. Moreover, the fuel cell assembled by this catalyst delivers a current density of 1.5 amperes per square centimeter at 0.6 volts and can operate steadily for at least 180 hours.

Mesoporous Nanostructured Composite Derived from Thermal Treatment CoFe Prussian Blue Analogue Cages and Electrodeposited NiCo-S as an Efficient Electrocatalyst for an Oxygen Evolution Reaction

Developing effective and priceless electrocatalysts is an indispensable requirement for advancing the efficiency of water splitting to get clean and sustainable fuels. Herein, we reported a feasible strategy for preparing a trimetallic (NiCoFe) superior electrocatalyst with a novel open-cage/3D frame-like structure for an oxygen evolution reaction (OER). It is prepared by consequent thermal treatments of a CoFe Prussian blue analogue frame/cage-like structure under an argon (CoFeA-TT) atmosphere and then electrochemical deposition of nickel-cobalt sulfide nanosheets as a shell layer on it. The electrochemical measurements demonstrated that the deposition of NiCo-S on CoFeA-TT (NiCo-S@CoFeA-TT) has the best catalytic performance and can drive the benchmark current density of 10 mA cm^-2 at a low overpotential of 268 mV with a Tafel slope of 62 mV dec^-1 and an excellent long-term catalytic stability in an alkaline medium. Its outstanding electrocatalytic performances are endowed from frame/cage-like structures, highly exposed active sites, accelerated mass and electron transport, and the synergistic effect of multiple hybrid components. The NiCo-S@CoFeA-TT showed a better performance than most advanced nonprecious catalysts and the noble commercial RuO₂ catalyst. This study exhibited an effective and efficient procedure to design 3D porous architecture catalysts for the energy-relevant electrocatalysis reaction.

Mesoporous Pt@PtM (M = Co, Ni) cage-bell nanostructures toward methanol electro-oxidation

Rational design of Pt-based nanostructures with a controllable morphology and composition is vital for electrocatalysis. Herein, we demonstrate a dual-template strategy to fabricate well-defined cage-bell nanostructures including a Pt core and a mesoporous PtM (M = Co, Ni) bimetallic shell (Pt@mPtM (M = Co, Ni) CBs). Owing to their unique nanostructure and bimetallic properties, Pt@mPtM (M = Co, Ni) CBs show higher catalytic activity, better durability and stronger CO tolerance for the methanol oxidation reaction than commercial Pt/C. This work provides a general method for convenient preparation of cage-bell nanostructures with a mesoporous bimetallic shell, which have high promising potential for application in electrocatalytic fields.

Direct Observation of Dynamic Bond Evolution in Single-Atom Pt/C3 N4 Catalysts

Single-atom catalysts are promising platforms for heterogeneous catalysis, especially for clean energy conversion, storage, and utilization. Although great efforts have been made to examine the bonding and oxidation state of single-atom catalysts before and/or after catalytic reactions, when information about dynamic evolution is not sufficient, the underlying mechanisms are often overlooked. Herein, we report the direct observation of the charge transfer and bond evolution of a single-atom Pt/C₃ N₄ catalyst in photocatalytic water splitting by synchronous illumination X-ray photoelectron spectroscopy. Specifically, under light excitation, we observed Pt-N bond cleavage to form a Pt⁰ species and the corresponding C=N bond reconstruction; these features could not be detected on the metallic platinum-decorated C₃ N₄ catalyst. As expected, H₂ production activity (14.7 mmol h^-1  g^-1 ) was enhanced significantly with the single-atom Pt/C₃ N₄ catalyst as compared to metallic Pt-C₃ N₄ (0.74 mmol h^-1  g^-1 ).

Atomic-Level Construction of Tensile-Strained PdFe Alloy Surface toward Highly Efficient Oxygen Reduction Electrocatalysis

Exploring the high-performance non-Pt electrocatalysts for oxygen reduction reaction (ORR), the bottleneck process in fuel cells, is desirable but challenging. Here, we report the Pd@PdFe core-shell icosahedra as an active and durable electrocatalyst toward ORR in alkaline conditions, which feature a three-atomic-layer tensile-strained PdFe overlayer on Pd icosahedra. Our optimized catalyst shows 2.8-fold enhancement in mass activity and 6.9-fold enhancement in specific activity than commercial Pt/C catalyst toward ORR, representing one of the best non-Pt electrocatalysts. Moreover, the boosted ORR catalysis is strongly supported by the assembled fuel cell performance using Pd@PdFe core-shell icosahedra as the cathode electrocatalyst. The density functional theory calculations reveal that the synergistic coupling of tensile strain and alloy effects enables the optimum binding strength for intermediates, thus causing the maximum activity. The present work suggests the coupling between multiple surface modulations endows larger room for the rational design of remarkable catalysts.

Continuous syntheses of carbon-supported Pd and Pd@Pt core-shell nanoparticles using a flow-type single-mode microwave reactor

Continuous syntheses of carbon-supported Pd@Pt core-shell nanoparticles were performed using microwave-assisted flow reaction in polyol to synthesize carbon-supported core Pd with subsequent direct coating of a Pt shell. By optimizing the amount of NaOH, almost all Pt precursors contributed to shell formation without specific chemicals.

Template Regeneration in Galvanic Replacement: A Route to Highly Diverse Hollow Nanostructures

The ability to produce a diverse spectrum of hollow nanostructures is central to the advances in many current and emerging areas of technology. Herein, we report a general method to craft hollow nanostructures with highly tunable physical and chemical parameters. The key strategy is to regenerate the nanoscale sacrificial templates in a galvanic replacement reaction through site-selective overgrowth. As examples, we demonstrate the syntheses of nanocages and nanotubes made of silver, gold, palladium, and/or platinum with well-controlled wall thicknesses and elemental distributions. Using the nanocages of silver and gold as models, we demonstrate they possess intriguing plasmonic properties and offer superior performance in biosensing applications. This study provides a powerful platform to customize hollow nanostructures with desired properties and therefore is expected to enable a variety of fundamental studies and technologically important applications.

Single Atom on the 2D Matrix: An Emerging Electrocatalyst for Energy Applications

The electrochemical energy conversions play an essential role in the production of sustainable and renewable energy. However, the performance is not up to the mark due to the absence of highly efficient and stable electrocatalysts. Recently, both 2D-matrix and single-atom catalysts (SACs) are two intense research topics in the field of electrocatalysis due to the high activity and stability and to maximize the utilization efficiency. Engineering the materials from 3D to 2D and modification from nanoparticles to single atoms have created a significant enhancement in the electrocatalytic activity. Hybridizing both the 2D matrix and SACs (2DM@SACs) creates a new electronic state in the materials, and that bequeaths with enhancing potentials toward the electrocatalytic activity. The strong covalent interaction between the 2D matrix and SACs tunes the intrinsic activity of the electrocatalysts. In this mini-review, we have discussed the different synthesis methods of 2DM@SACs with a focus on their electrochemical energy applications such as hydrogen evolution, oxygen evolution, oxygen reduction, and carbon dioxide reduction. This mini-review appraises the contribution to the rational proposal for the synthesis of perfect 2DM@SAC catalysts with their electrochemical properties toward energy conversion applications.

Covalent organic framework-supported platinum nanoparticles as efficient electrocatalysts for water reduction

The hydrogen evolution reaction (HER) is one of the most effective and sustainable ways to produce hydrogen gas as an alternative clean fuel. The rate of this electrocatalytic reaction is highly dependent on the properties (dispersity and stability) of electrocatalysts. Herein, we developed well-dispersed and highly stable platinum nanoparticles (PtNPs) supported on a covalent organic framework (COF-bpyTPP), which exhibit excellent catalytic activities toward HER as well as the hydride reduction reaction. The nanoparticles have an average size of 2.95 nm and show superior catalytic performance compared to the commercially available Pt/C under the same alkaline conditions, producing 13 times more hydrogen with a far more positive onset potential (-0.13 V vs.-0.63 V) and ca. 100% faradaic efficiency. The reaction rate of the hydride reduction of 4-nitrophenol was also 10 times faster in the case of PtNPs@COF compared to the commercial Pt/C under the same loading and conditions. More importantly, the PtNPs@COF are highly stable under the aqueous reactions conditions and can be reused without showing noticeable aggregation and activity degradation.

Customizable Ligand Exchange for Tailored Surface Property of Noble Metal Nanocrystals

It is highly desirable, while still challenging, to obtain noble metal nanocrystals with custom capping ligands, because their colloidal synthesis relies on specific capping ligands for the shape control while conventional ligand exchange processes suffer from "the strong replaces the weak" limitation, which greatly hinders their applications. Herein, we report a general and effective ligand exchange approach that can replace the native capping ligands of noble metal nanocrystals with virtually any type of ligands, producing flexibly tailored surface properties. The key is to use diethylamine with conveniently switchable binding affinity to the metal surface as an intermediate ligand. As a strong ligand, it in its original form can effectively remove the native ligands; while protonated, it loses its binding affinity and facilitates the adsorption of new ligands, especially weak ones, onto the metal surface. By this means, the irreversible order in the conventional ligand exchange processes could be overcome. The efficacy of the strategy is demonstrated by mutual exchange of the capping ligands among cetyltrimethylammonium, citrate, polyvinylpyrrolidone, and oleylamine. This novel strategy significantly expands our ability to manipulate the surface property of noble metal nanocrystals and extends their applicability to a wide range of fields, particularly biomedical applications.

Recover the activity of sintered supported catalysts by nitrogen-doped carbon atomization

The sintering of supported metal nanoparticles is a major route to the deactivation of industrial heterogeneous catalysts, which largely increase the cost and decrease the productivity. Here, we discover that supported palladium/gold/platinum nanoparticles distributed at the interface of oxide supports and nitrogen-doped carbon shells would undergo an unexpected nitrogen-doped carbon atomization process against the sintering at high temperatures, during which the nanoparticles can be transformed into more active atomic species. The in situ transmission electron microscopy images reveal the abundant nitrogen defects in carbon shells provide atomic diffusion sites for the mobile atomistic palladium species detached from the palladium nanoparticles. More important, the catalytic activity of sintered and deactivated palladium catalyst can be recovered by this unique N-doped carbon atomization process. Our findings open up a window to preparation of sintering-resistant single atoms catalysts and regeneration of deactivated industrial catalysts.

Visualization Analysis of Pt and Co Species in Degraded Pt3Co/C Electrocatalyst Layers of a Polymer Electrolyte Fuel Cell Using a Same-View Nano-XAFS/STEM-EDS Combination Technique

In order to obtain a suitable design policy for the development of a next-generation polymer electrolyte fuel cell, we performed a visualization analysis of Pt and Co species following aging and degradation processes in membrane-electrode assembly (MEA), using a same-view. Nano-X-ray absorption fine structure (XAFS)/Scanning transmission electron microscope (STEM)-energy dispersive X-ray spectroscopy (EDS) technique that we developed to elucidate durability factors and degradation mechanisms of a MEA Pt₃Co/C cathode electrocatalyst with higher activity and durability than a MEA Pt/C. In the MEA Pt₃Co/C, after 5000 ADT-rec (rectangle accelerated durability test) cycles, unlike the MEA Pt/C, there was no oxidation of Pt. In contrast, Co oxidized and dissolved over a wide range of the cathode layer (∼70% of the initial Co amount). The larger the size of the cracks and pores in the MEA Pt/C and the smaller the ratio of Pt/ionomer of cracks and pores, the faster the rate of catalyst degradation. In contrast, there was no correlation between the size or Co/ionomer ratio of the cracks and pores and the Co dissolution of the MEA Pt₃Co/C. It was shown that Co dissolved in the electrolyte region had an octahedral Co²⁺-O₆ structure, based on a 150 nm × 150 nm nano-XAFS analysis. It was also shown that its existence suppressed the oxidation and dissolution of Pt. The MEA Pt₃Co/C after 10,000 ADT-rec cycles had many cracks and pores in the cathode electrocatalyst layer, and about 90% of Co had been dissolved and removed from the cathode layer. We discovered a metallic Pt-Co alloy band in the electrolyte region of 300-400 nm from the cathode edge and square planar Pt²⁺-O₄ species and octahedral Co²⁺-O₆ species in the area between the cathode edge and the Pt-Co band. The transition of Pt and Co chemical species in the Pt₃Co/C cathode electrocatalyst in the MEA during the degradation process, as well as a fuel cell deterioration suppression process by Co were visualized for the first time at the nano scale using the same-view nano-XAFS/STEM-EDS combination technique that can measure the MEA under a humid N₂ atmosphere while maintaining the working environment for a fuel cell.

Probing the active sites of site-specific nitrogen doping in metal-free graphdiyne for electrochemical oxygen reduction reactions

The development of highly active and low-cost catalysts for electrochemical reactions is one of the most attractive topics in the renewable energy technology. Herein, the site-specific nitrogen doping of graphdiyne (GDY) including grap-N, sp-N(I) and sp-N(II) GDY is systematically investigated as metal-free oxygen reduction electrocatalysts via density functional theory (DFT). Our results indicate that the doped nitrogen atom can significantly improve the oxygen (O₂) adsorption activity of GDY through activating its neighboring carbon atoms. The free-energy landscape is employed to describe the electrochemical oxygen reduction reaction (ORR) in both O₂ dissociation and association mechanisms. It is revealed that the association mechanism can provide higher ORR onset potential than dissociation mechanism on most of the substrates. Especially, sp-N(II) GDY exhibits the highest ORR electrocatalytic activity through increasing the theoretical onset potential to 0.76 V. This work provides an atomic-level insight for the electrochemical ORR mechanism on metal-free N-doped GDY.

Integration mesoporous surface and hollow cavity into PtPdRh nano-octahedra for enhanced oxygen reduction electrocatalysis

Design and synthesis of Pt-based nanocrystals with controlled structural diversity and complexity can potentially bring about multifunctional properties. In this work, we present a facile two-step strategy for the construction of the PtPdRh mesoporous octahedral nanocages (PtPdRh MONCs). This unique nanoarchitectonics rationally integrates multiple advantages (i.e. the octahedral shape, hollow cavity and mesoporous surface) into one catalyst, which facilitates the efficient utilization of noble metal atoms at both of the interior and exterior surfaces. As expected, the resultant PtPdRh MONCs could effectively catalyze the oxygen reduction reaction (ORR) under acidic conditions. The demonstrated ORR activity and catalytic durability are superior to the commercial Pt/C catalyst. The present study would provide a general guidance for architectural and compositional engineering of noble metal nanocrystals with desired functionalities and properties.

Origin of High Activity and Durability of Twisty Nanowire Alloy Catalysts under Oxygen Reduction and Fuel Cell Operating Conditions

The ability to control the surface composition and morphology of alloy catalysts is critical for achieving high activity and durability of catalysts for oxygen reduction reaction (ORR) and fuel cells. This report describes an efficient surfactant-free synthesis route for producing a twisty nanowire (TNW) shaped platinum-iron (PtFe) alloy catalyst (denoted as PtFe TNWs) with controllable bimetallic compositions. PtFe TNWs with an optimal initial composition of ∼24% Pt are shown to exhibit the highest mass activity (3.4 A/mg_Pt, ∼20 times higher than that of commercial Pt catalyst) and the highest durability (<2% loss of activity after 40 000 cycles and <30% loss after 120 000 cycles) among all PtFe-based nanocatalysts under ORR or fuel cell operating conditions reported so far. Using ex situ and in situ synchrotron X-ray diffraction coupled with atomic pair distribution function (PDF) analysis and 3D modeling, the PtFe TNWs are shown to exhibit mixed face-centered cubic (fcc)-body-centered cubic (bcc) alloy structure and a significant lattice strain. A striking finding is that the activity strongly depends on the composition of the as-synthesized catalysts and this dependence remains unchanged despite the evolution of the composition of the different catalysts and their lattice constants under ORR or fuel cell operating conditions. Notably, dealloying under fuel cell operating condition starts at phase-segregated domain sites leading to a final fcc alloy structure with subtle differences in surface morphology. Due to a subsequent realloying and the morphology of TNWs, the surface lattice strain observed with the as-synthesized catalysts is largely preserved. This strain and the particular facets exhibited by the TNWs are believed to be responsible for the observed activity and durability enhancements. These findings provide new insights into the correlation between the structure, activity, and durability of nanoalloy catalysts and are expected to energize the ongoing effort to develop highly active and durable low-Pt-content nanowire catalysts by controlling their alloy structure and morphology.

Nanomaterials in electrochemical cytosensors

Nano-electrochemical cytosensors have attracted intensive attention and achieved huge progress in the biomedical field owing to their stability, rapidity, accuracy, and low-cost properties.

Bonding–antibonding state transition induces multiple electron modulations toward oxygen reduction reaction electrocatalysis

B doping induces the transformation from the bonding state to the antibonding state of an Ni–N bond, resulting in enhanced ORR activity.

Degradation of the transition metal@Pt core–shell nanoparticle catalyst: a DFT study

Electrocatalysts in acidic media face the issues of inactivation and degradation with complex thermodynamic processes.

Sub-3 nm Intermetallic Ordered Pt3In Clusters for Oxygen Reduction Reaction

Industrial applications of Pt-based oxygen-reduction-reaction (ORR) catalysts are limited by high cost and low stability. Here, facile large-scale synthesis of sub-3-nm ordered Pt3In clusters on commercial carbon black as ORR catalyst that alleviates both these shortcomings is reported. As-prepared Pt3In/C exhibits a mass activity of 0.71 mA mg-1 and a specific area activity of 0.91 mA cm-2 at 0.9 V vs reversible hydrogen electrode, which are 4.1 and 2.7 times the corresponding values of commercial Pt/C catalysts. The as-prepared ordered Pt3In/C catalyst is also remarkably stable with negligible activity and structural decay after 20 000 accelerated electrochemical durability cycles, due to its ordered structure. Density-functional-theory calculations demonstrate that ordered-Pt3In is more energetically favorable for ORR than the commercial Pt/C catalysts because ∆G O is closer to the peak of the volcano plot after ordered incorporation of indium atoms.

Visualization and understanding of the degradation behaviors of a PEFC Pt/C cathode electrocatalyst using a multi-analysis system combining time-resolved quick XAFS, three-dimensional XAFS-CT, and same-view nano-XAFS/STEM-EDS techniques

We developed a multi-analysis system that can measure in situ time-resolved quick XAFS and in situ three-dimensional XAFS-CT in the same area of a cathode electrocatalyst layer in a membrane-electrode assembly of a polymer electrolyte fuel cell.

Heterogeneous assembly of Pt-clusters on hierarchically structured CoOx@SnPd2@SnO2 quaternary nanocatalysts manifesting oxygen reduction reaction performance

Atomic Pt clusters in the heterogeneous interface of CoO_x@SnPd₂@SnO₂ possess high heteroatomic intermixing facilities, oxygen splitting and hydration reactions resulting in high performance ORR.

Multinary PtPdNiP truncated octahedral mesoporous nanocages for enhanced methanol oxidation electrocatalysis

Multinary PtPdNiP TOMNs have been synthesized for the electrocatalytic methanol oxidation reaction with a superior electrocatalytic performance.

A dinuclear cobalt cluster as electrocatalyst for oxygen reduction reaction

Dinuclear metal clusters as metalloenzymes execute efficient catalytic activities in biological systems. Enlightened by this, a dinuclear {CoII 2} cluster was selected to survey its ORR (Oxygen Reduction Reaction) catalytic activities. The crystalline {CoII 2} possesses defined structure and potential catalytic active centers of {CoN4O2} sites, which was identified by X-ray single crystal diffraction, Raman and XPS. The appropriate supramolecular porosity combining abundant pyridinic-N and triazole-N sites of {CoII 2} catalyst synergistically benefit the ORR performance. As a result, this non-noble metal catalyst presents a nice ORR electrocatalytic activity and abides by a nearly 4-electron reduction pathway. Thus, this unpyrolyzed crystalline catalyst clearly provide precise active sites and the whole defined structural information, which can help researcher to design and fabricate efficient ORR catalysts to improve their activities. Considering the visible crystal structure, a single cobalt center-mediated catalytic mechanism was also proposed to elucidate the ORR process.

The importance of nanoscale confinement to electrocatalytic performance

Electrocatalytic nanoparticles that mimic the three-dimensional geometric architecture of enzymes where the reaction occurs down a substrate channel isolated from bulk solution, referred to herein as nanozymes, were used to explore the impact of nano-confinement on electrocatalytic reactions. Surfactant covered Pt-Ni nanozyme nanoparticles, with Ni etched from the nanoparticles, possess a nanoscale channel in which the active sites for electrocatalysis of oxygen reduction are located. Different particle compositions and etching parameters allowed synthesis of nanoparticles with different average substrate channel diameters that have varying amounts of nano-confinement. The results showed that in the kinetically limited regime at low overpotentials, the smaller the substrate channels the higher the specific activity of the electrocatalyst. This is attributed to higher concentrations of protons, relative to bulk solution, required to balance the potential inside the nano-confined channel. However, at higher overpotentials where limitation by mass transport of oxygen becomes important, the nanozymes with larger substrate channels showed higher electrocatalytic activity. A reaction-diffusion model revealed that the higher electrocatalytic activity at low overpotentials with smaller substrate channels can be explained by the higher concentration of protons. The model suggests that the dominant mode of mass transport to achieve these high concentrations is by migration, exemplifying how nano-confinement can be used to enhance reaction rates. Experimental and theoretical data show that under mass transport limiting potentials, the nano-confinement has no effect and the reaction only occurs at the entrance of the substrate channel at the nanoparticle surface.

Hollow PdAg-CeO2 heterodimer nanocrystals as highly structured heterogeneous catalysts

In the present work, hollow PdAg-CeO₂ heterodimer nanocrystals (NCs) were prepared and tested as catalysts for the selective hydrogenation of alkynes. These nanostructures combine for the first time the beneficial effect of alloying Pd with Ag in a single NC hollow domain with the formation of active sites at the interface with the CeO₂ counterpart in an additive manner. The PdAg-CeO₂ NCs display excellent alkene selectivity for aliphatic alkynes. For the specific case of hydrogenation of internal alkynes such as 4-octyne, very low over-hydrogenation and isomerization products were observed over a full conversion regime, even after prolonged reaction times. These catalytic properties were remarkably superior in comparison to standard catalysts. The promotion of Ag on the moderation of the reactivity of the Pd phase, in combination with the creation of interfacial sites with the CeO₂ moiety in the same nanostructure, is pointed as the responsible of such a remarkable catalytic performance.