Co Nanoparticles Encapsulated in N‑Doped Carbon Nanosheets: Enhancing Oxygen Reduction Catalysis without Metal–Nitrogen Bonding

It is known that introducing metal nanoparticles (e.g., Fe and Co) into N-doped carbons can enhance the activity of N-doped carbons toward the oxygen reduction reaction (ORR). However, introducing metals into N-doped carbons inevitably causes the formation of multiple active sites. Thus, it is challenging to identify the active sites and unravel mechanisms responsible for enhanced ORR activity. Herein, by developing a new N-heterocyclic carbene (NHC)–Co complex as the nitrogen- and metal-containing precursor, we report the synthesis of N-doped carbon nanosheets embedded with Co nanoparticles as highly active ORR catalysts without direct metal–nitrogen bonding. Electrochemical measurements and X-ray absorption spectroscopy indicate that the carbon–nitrogen sites surrounding Co nanoparticles are responsible for the observed ORR activity and stability. Density functional theory calculations further reveal that Co nanoparticles could facilitate the protonation of O₂ and thus promote the ORR activity. These results provide new prospects in the rational design and synthesis of heteroatom-doped carbon materials as non-precious-metal catalysts for various electrochemical reactions

Role of Ru Oxidation Degree for Catalytic Activity in Bimetallic Pt/Ru Nanoparticles

Understanding the intrinsic relationship between the catalytic activity of bimetallic nanoparticles and their composition and structure is very critical to further modulate their properties and specific applications in catalysts, clean energy, and other related fields. Here we prepared new bimetallic Pt–Ru nanoparticles with different Pt/Ru molar ratios via a solvothermal method. In combination with X-ray diffraction (XRD), transmission electron microscopy (TEM) coupled with energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and synchrotron X-ray absorption spectroscopy (XAS) techniques, we systematically investigated the dependence of the methanol electro-oxidation activity from the obtained Pt/Ru nanoparticles with different compositions under annealing treatment. Our observations revealed that the Pt–Ru bimetallic nanoparticles have a Pt-rich core and a Ru-rich shell structure. After annealment at 500 °C, the alloying extent of the Pt–Ru nanoparticles increased, and more Pt atoms appeared on the surface. Notably, subsequent evaluations of the catalytic activity for the methanol oxidation reaction proved that the electrocatalytic performance of Pt/Ru bimetals was increased with the oxidation degree of superficial Ru atoms

Engineering Phase Transition from 2H to 1T in MoSe₂ by W Cluster Doping toward Lithium-Ion Battery

Phase engineering synthesis strategy is extremely challenging to achieve stable metallic phase molybdenum diselenide for a better physicochemical property than the thermodynamically stable semiconducting phase. Herein, we introduce tungsten atom clusters into the MoSe2 layered structure, realizing the phase transition from the 2H semiconductor to 1T metallic phase at a high temperature. The combination of synchrotron radiation X-ray absorption spectroscopy, Cs-corrected transmission electron microscopy, and theoretical calculation demonstrates that the aggregation doping of W atoms is the factor of MoSe2 structure transformation. When utilizing this distinct structure as an anode component, it demonstrates outstanding rate capability and durability. After 500 cycles, this results in a specific capacity of 1007.4 mAh g–1 at 500 mA g–1. These discoveries could open the door for the future development of high-performance anodes for ion battery applications

Unveiling the Critical Relationship between MXene Double-Layer Capacitance and Electronic Configuration

MXene, with highly tunable and controllable surface terminations, is an emerging electrode material for electric double-layer (EDL) capacitors used in electrochemical energy storage. However, the influence of alterations in the electronic configuration of MXene induced by modifications in functional groups on EDL capacitance remains elusive. Thus, an implicit self-consistent electrolyte model is developed to investigate the EDL capacitance and structure of Mo2CTx MXene as a function of electronic configuration at an atomic scale. We reveal a strong correlation between the electronic configurations of metal Mo in Mo2CTx MXene and its EDL capacitance, with the dz2 orbital of Mo perpendicular to the MXene surface playing a crucial role. The higher EDL capacitance and thinner EDL thickness primarily originate from a lower number of occupied electrons in the d orbitals (higher unoccupied d orbitals) and a larger d-band occupied center. Furthermore, this relationship can be further extended to the halogen termination of MXene. Notably, by manipulating the surface terminations, the electronic configurations (occupied and unoccupied orbitals) of Mo orbitals can be regulated, thus providing a facilitative way to control the EDL capacitance. The results show that the EDL capacitance depends not only on the electrode–electrolyte interfacial structure but also on the electronic configuration. These findings provide a solid foundation for regulating the structure and capacitance of the EDL of MXene from an electronic perspective, which could have significant implications for the development of advanced energy storage devices

Strain Effect in Bimetallic Electrocatalysts in the Hydrogen Evolution Reaction

Unravelling the electrocatalytic activity origins of bimetallic nanomaterials is of great importance, yet fundamentally challenging. One of the main reasons for this is that the interactive contributions from geometric and electronic effects to enhancements in reaction activity are difficult to distinguish from one another. Here, on well-defined Ru–Pt core–shell (Ru@Pt) and homogeneous alloy (RuPt) model electrocatalysts, we are able to isolate these two effects. Furthermore, we observe the dominant role of strain in the intrinsic activity of the alkaline hydrogen evolution reaction. In the Ru@Pt icosahedral nanostructure, the highly strained Pt shells effectively accommodate the interfacial lattice mismatch from a face-centered cubic structured Ru core. This unique property leads to a weak binding of hydrogen and optimal interaction with hydroxyl species during the reaction, thus leading to an enhanced apparent activity of Ru@Pt

Initial Reaction Mechanism of Platinum Nanoparticle in Methanol–Water System and the Anomalous Catalytic Effect of Water

Understanding the detailed reaction mechanism in the early stage of noble metal nanoparticles is very critical for controlling the final crystal’s size, morphology, and properties. Here, we report a systematic study on the initial reaction mechanism of Pt nanoparticles in methanol–water system and demonstrate an anomalous catalytic effect of H₂O on the reduction of H₂PtCl₆ to Pt nanoparticles using a combination of UV–vis, X-ray absorption spectroscopy (XAS), liquid chromatography mass spectrometry (LCMS), and first-principles calculation methods. The observations reveal the transformation route [PtCl₆]^2– → [PtCl₅(CH₃O)]^2– → [PtCl₄]^2– → [PtCl₃(CH₃O)]^2– → [PtCl₂]^2– and finally to form Pt nanoparticles in a pure CH₃OH solution. With 10 vol % water adding in the CH₃OH solution, a new and distinct chemical reduction pathway is found in which the precursors change from [PtCl₆]^2– to [PtCl₅(CH₃O)­(H₂O)]^2– to [PtCl₄]^2– to [PtCl₃(CH₃O)­(H₂O)]^2– to [PtCl₂]^2– and to Pt nanoparticles. Notably, the supernumerary water molecular can significantly accelerate the rate of chemical reduction and greatly shorten the reaction time. This work not only elucidates the initial reaction mechanism of Pt nanoparticles but also highlights the pronounced influence of H₂O on the reaction pathway, which will provide useful insights for understanding the formation mechanism of noble metal nanoparticles and open up a high efficient way to synthesize new functional nanomaterial

Pyrazolate-Based Porphyrinic Metal–Organic Framework with Extraordinary Base-Resistance

Guided by a top-down topological analysis, a metal–organic framework (MOF) constructed by pyrazolate-based porphyrinic ligand, namely, PCN-601, has been rationally designed and synthesized, and it exhibits excellent stability in alkali solutions. It is, to the best of our knowledge, the first identified MOF that can retain its crystallinity and porosity in saturated sodium hydroxide solution (∼20 mol/L) at room temperature and 100 °C. This almost pushes base-resistance of porphyrinic MOFs (even if MOFs) to the limit in aqueous media and greatly extends the range of their potential applications. In this work, we also tried to interpret the stability of PCN-601 from both thermodynamic and kinetic perspectives

Pyrazolate-Based Porphyrinic Metal–Organic Framework with Extraordinary Base-Resistance

Guided by a top-down topological analysis, a metal–organic framework (MOF) constructed by pyrazolate-based porphyrinic ligand, namely, PCN-601, has been rationally designed and synthesized, and it exhibits excellent stability in alkali solutions. It is, to the best of our knowledge, the first identified MOF that can retain its crystallinity and porosity in saturated sodium hydroxide solution (∼20 mol/L) at room temperature and 100 °C. This almost pushes base-resistance of porphyrinic MOFs (even if MOFs) to the limit in aqueous media and greatly extends the range of their potential applications. In this work, we also tried to interpret the stability of PCN-601 from both thermodynamic and kinetic perspectives

Probing Lithium Storage Mechanism of MoO₂ Nanoflowers with Rich Oxygen-Vacancy Grown on Graphene Sheets

The search for new electrode materials is of paramount importance for the practical apply of lithium-ion batteries (LIBs). Herein, flower-like MoO₂ microislands consist of MoO₂ nanorods grown on both sides of graphene sheets were synthesized via a solvo-thermal method, followed by a simple thermal treatment in argon. Our EXAFS and ESR data suggest there oxygen-vacancies in MoO₂ of the FMMGS hybrids. Besides, by tunning the ratio of glucose and CTAB, samples with different oxygen-vacancies content were synthesized. When used as anode materials for lithium-ion batteries, the oxygen-vacancy-rich FMMGS hybrids exhibited obviously higher capacity, rate capability than any nonvacancy samples. Importantly, synchrotron-radiation-based X-ray absorption near-edge structure (XANES), extended X-ray absorption fine-structure (EXAFS) and ex situ X-ray diffraction (ex situ XRD) were employed to elucidate the Li-ion insertion and extraction processes in the MoO₂ electrode. Our data clearly revealed that Li₂MoO₄ was generated during the Li uptake/removal process, which can be attributed to the existence of abundant oxygen vacancies in MoO₂ microislands. This provides us a useful insight for better understanding of dynamic cycling behavior in various Mo-based electrodes

Atomically Intercalating Tin Ions into the Interlayer of Molybdenum Oxide Nanobelt toward Long-Cycling Lithium Battery

Atomic intercalation of different agents into 2D layered materials can engineer the intrinsic structure on the atomic scale and thus tune the physical and chemical properties for specific applications. Here we successfully introduce tin (Sn) atoms into the interlayer of α-MoO₃ nanobelts forming a new MoO₃–Sn intercalation with ultrastable structure. Combining with theoretical calculations, our synchrotron radiation-based characterizations and electron microscope observations clearly reveal that the intercalated Sn atoms could bond with five O atoms, forming a pentahedral structure. Subsequently, the Sn–O bonds induce a less distorted [MoO₆] octahedral structure, resulting in a unique structure that is distinct with pristine α-MoO₃ or any other molybdenum oxides. Employed as anode for lithium-ion battery, the as-prepared MoO₃–Sn nanobelts display a much higher capacity of 520 mAhg^–1 at 500 mAg^–1 than α-MoO₃ nanobelts (291 mAhg^–1), with a Coulombic efficiency of 99.5%. Moreover, owing to the strong intercalation from Sn ions, the MoO₃–Sn nanobelts pose superior cyclability, durability, and reliability