Fabrication of Low Adsorption Energy Ni–Mo Cluster Cocatalyst in Metal–Organic Frameworks for Visible Photocatalytic Hydrogen Evolution

An effective cocatalyst is crucial for enhancing the visible photocatalytic performance of the hydrogen generation reaction. By using density-functional theory (DFT) and frontier molecular orbital (FMO) theory calculation analysis, the hydrogen adsorption free energy (Δ<i>G</i>_H) of Ni–Mo alloy (458 kJ·mol^–1) is found to be lower than that of Ni itself (537 kJ·mol^–1). Inspired by these results, the novel, highly efficient cocatalyst NiMo@MIL-101 for photocatalysis of the hydrogen evolution reaction (HER) was fabricated using the double solvents method (DSM). In contrast with Ni@MIL-101 and Mo@MIL-101, NiMo@MIL-101 exhibited an excellent photocatalytic performance (740.2 μmol·h^–1 for HER), stability, and high apparent quantum efficiency (75.7%) under 520 nm illumination at pH 7. The NiMo@MIL-101 catalyst also showed a higher transient photocurrent, lower overpotential (−0.51 V), and longer fluorescence lifetime (1.57 ns). The results uncover the dependence of the photocatalytic activity of HER on the Δ<i>G</i>_H of Ni–Mo (MoNi₄) alloy nanoclusters, i.e., lower Δ<i>G</i>_H corresponding to higher HER activity for the first time. The NiMo@MIL-101 catalyst could be a promising candidate to replace precious-metal catalysts of the HER

PdCu@Pd Nanocube with Pt-like Activity for Hydrogen Evolution Reaction

The electronic properties of metal surfaces can be modulated to weaken the binding energy of adsorbed H-intermediates on the catalyst surface, thus enhancing catalytic activity for the hydrogen evolution reaction (HER). Here we first prepare PdCu alloy nanocubes (NCs) by coreduction of Cu­(acac)₂ (acac = acetylacetonate) and Na₂PdCl₄ in the presence of oleylamine (OAm) and trioctylphosphine (TOP). The PdCu NC coated glassy carbon electrode is then anodized at a constant potential of 0.51 V vs Ag/AgCl at room temperature in 0.5 M H₂SO₄ solution for 10 s, which converts PdCu NCs into core@shell PdCu@Pd NCs that show much enhanced Pt-like activity for the HER and much more robust durability. The improvements in surface property and HER activity are rationalized based on strain and ligand effects that enhance the activity of the edge-exposed Pd atoms on core@shell PdCu@Pd structure. This work opens up a new perspective for simultaneously reducing metal Pd cost and achieving excellent performance toward the HER

Metal-Free Mesoporous SiO₂ Nanorods as a Highly Efficient Catalyst for the Baeyer–Villiger Oxidation under Mild Conditions

The development of efficient and environmentally friendly catalysts for oxidative reaction is of great importance in applied catalysis. In this work, a simple and environmentally benign approach for highly selective preparation of ε-caprolactone by oxidation of cyclohexanone has been carried out, which employed metal-free mesoporous silica (mSiO₂) nanorods as catalyst under atmospheric pressure. The metal-free silica catalyst was applied for the first time in the Baeyer–Villiger (B–V) oxidation reaction. It showed efficient catalytic performance for the B–V oxidation of various cyclic ketones and aliphatic ketones with O₂/benzaldehyde as oxidant. The catalyst could be easily separated from the reaction system by filtration and reused several times without significance loss of activity. Moreover, electron paramagnetic resonance (EPR) spectra of the reaction were obtained, indicating the existence of benzoyloxyl radical. The mechanism study of the reaction demonstrated that the super large surface area diluted the concentration of radicals and the adsorption of radicals could protect the radical species from inhibition

Lateral-Size-Mediated Efficient Oxygen Evolution Reaction: Insights into the Atomically Thin Quantum Dot Structure of NiFe₂O₄

The study of high-performance electrocatalysts for driving the oxygen evolution reaction (OER) is important for energy storage and conversion systems. As a representative of inverse-spinel-structured oxide catalysts, nickel ferrite (NiFe₂O₄) has recently gained interest because of its earth abundance and environmental friendliness. However, the gained electrocatalytic performance of NiFe₂O₄ for the OER is still far from the state-of-the-art requirements because of its poor reactivity and finite number of surface active sites. Here, we prepared a series of atomically thin NiFe₂O₄ catalysts with different lateral sizes through a mild and controllable method. We found that the atomically thin NiFe₂O₄ quantum dots (AT NiFe₂O₄ QDs) show the highest OER performance with a current density of 10 mA cm^–2 at a low overpotential of 262 mV and a small Tafel slope of 37 mV decade^–1. The outstanding OER performance of AT NiFe₂O₄ QDs is even comparable to that of commercial RuO₂ catalyst, which can be attributed to its high reactivity and the high fraction of active edge sites resulting from the synergetic effect between the atomically thin thickness and the small lateral size of the atomically thin quantum dot (AT QD) structural motif. The experimental results reveal a negative correlation between lateral size and OER performance in alkaline media. Specifically speaking, the number of low-coordinated oxygen atoms increases with decreasing lateral size, and this leads to significantly more oxygen vacancies that can lower the adsorption energy of H₂O, increasing the catalytic OER efficiency of AT NiFe₂O₄ QDs

Palladium Nanoparticles Anchored on Three-Dimensional Nitrogen-Doped Carbon Nanotubes as a Robust Electrocatalyst for Ethanol Oxidation

Palladium nanoparticles were uniformly anchored on nitrogen-doped carbon nanotubes with a three-dimensional network structure (denoted as Pd/3DNCNTs) through a facile, surfactant-free, and green approach with ethanol as the reducing agent. As a robust catalyst for the ethanol electrocatalytic oxidation reaction (EOR), Pd/3DNCNTs exhibit superior improved electrocatalytic activity, accelerated kinetics, and robust stability, mainly attributed to the unique architecture features of the 3DNCNTs. The results of this part of the work reveal that the Pd/3DNCNTs with an infusive electrochemical property for EOR are promising for direct ethanol fuel cells (DEFCs) and various other applications in electrochemistry. Additionally, the green approach probably provides some new ideas for the design of other new catalysts for fuel cells