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

Integrated Flexible Electrode for Oxygen Evolution Reaction: Layered Double Hydroxide Coupled with Single-Walled Carbon Nanotubes Film

The integration of active components and conductive supports forming free-standing electrodes is highly desirable for a series of energy storage and conversion devices. Herein, a facile hydrothermal method is developed to achieve the coupling of NiFe layered double hydroxide (LDH) and single-walled carbon nanotubes (SWNT) film, forming an integrated flexible electrode for oxygen evolution reaction (OER). The electrode requires a low overpotential of 250 mV to reach a current density of 10 mA cm^–2 in 1 M KOH, and shows rapid reaction kinetics with a Tafel slope of 35 mV dec^–1. Advanced soft X-ray absorption near-edge structure measurements efficiently indicate strong interfacial electron coupling between the LDH and SWNT, which authentically contributes to superior OER performance. This work provides a new strategy to design binder-free and flexile electrodes for practical application

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

Monolayer Thiol Engineered Covalent Interface toward Stable Zinc Metal Anode

Interface engineering of zinc metal anodes is a promising remedy to relieve their inferior stability caused by dendrite growth and side reactions. Nevertheless, the low affinity and additional weight of the protective coating remain obstacles to their further implementation. Here, aroused by DFT simulation, self-assembled monolayers (SAMs) are selectively constructed to enhance the stability of zinc metal anodes in dilute aqueous electrolytes. It is found that the monolayer thiol molecules relatively prefer to selectively graft onto the unstable zinc crystal facets through strong Zn–S chemical interactions to engineer a covalent interface, enabling the uniform deposition of Zn2+ onto (002) crystal facets. Therefore, dendrite-free anodes with suppressed side reactions can be achieved, proven by in situ optical visualization and differential electrochemical mass spectrometry (DEMS). In particular, the thiol endows the symmetric cells with a 4000 h ultrastable plating/stripping at a specific current density of 1.0 mA cm–2, much superior to those of bare zinc anodes. Additionally, the full battery of modified anodes enables stable cycling of 87.2% capacity retention after 3300 cycles. By selectively capping unstable crystal facets with inert molecules, this work provides a promising design strategy at the molecular level for stable metal anodes

X‑ray Insights into Formation of −O Functional Groups on MXenes: Two-Step Dehydrogenation of Adsorbed Water

Engineered MXene surfaces with more −O functional groups are feasible for realizing higher energy density due to their higher theoretical capacitance. However, there have been only a few explorations of this regulation mechanism. Investigating the formation source and mechanism is conducive to expanding the adjustment method from the top-down perspective. Herein, for the first time, the formation dynamics of −O functional groups on Mo2CTx are discovered as a two-step dehydrogenation of adsorbed water through in situ near-ambient-pressure X-ray photoelectron spectroscopy, further confirmed by ab initio molecular dynamics simulations. From this, the controllable substitution of −F functional groups with −O functional groups is achieved on Mo2CTx during electrochemical cycling in an aqueous electrolyte. The obtained Mo2CTx with rich −O groups exhibits a high capacitance of 163.2 F g –1 at 50 mV s –1, together with excellent stability. These results offer new insights toward engineering surface functional groups of MXenes for many specific applications

Facile Synthesis of Hierarchical Cu₂MoS₄ Hollow Sphere/Reduced Graphene Oxide Composites with Enhanced Photocatalytic Performance

We present a controllable synthesis of ternary hierarchical hollow sphere, assembling by numerous particle-like Cu₂MoS₄, via a facile hydrothermal method. By adding graphene oxides (GO) in the reaction process, Cu₂MoS₄/reduced graphene oxide (RGO) heterostructures were obtained with enhanced photocurrent and photocatalytic performance. As demonstrated by electron microscopy observations and X-ray characterizations, considerable interfacial contact was achieved between hierarchical Cu₂MoS₄ hollow sphere and RGO, which could facilitate the separation of photoinduced electrons and holes within the hybrid structure. In comparison with the pure Cu₂MoS₄ hollow sphere, the obtained hybrid structures exhibited significantly enhanced light absorption property and the ability of suppressing the photoinduced electron–holes recombination, which led to significant enhancement in both photocurrent and efficiency of photocatalytic methyl orange (MO) degradation under visible light (λ > 420 nm) irradiation

X‑ray Insights into Formation of −O Functional Groups on MXenes: Two-Step Dehydrogenation of Adsorbed Water

Engineered MXene surfaces with more −O functional groups are feasible for realizing higher energy density due to their higher theoretical capacitance. However, there have been only a few explorations of this regulation mechanism. Investigating the formation source and mechanism is conducive to expanding the adjustment method from the top-down perspective. Herein, for the first time, the formation dynamics of −O functional groups on Mo2CTx are discovered as a two-step dehydrogenation of adsorbed water through in situ near-ambient-pressure X-ray photoelectron spectroscopy, further confirmed by ab initio molecular dynamics simulations. From this, the controllable substitution of −F functional groups with −O functional groups is achieved on Mo2CTx during electrochemical cycling in an aqueous electrolyte. The obtained Mo2CTx with rich −O groups exhibits a high capacitance of 163.2 F g –1 at 50 mV s –1, together with excellent stability. These results offer new insights toward engineering surface functional groups of MXenes for many specific applications