Zhijun Li

Uncoordinated Amine Groups of Metal–Organic Frameworks to Anchor Single Ru Sites as Chemoselective Catalysts toward the Hydrogenation of Quinoline

Here we report a precise control of isolated single ruthenium site supported on nitrogen-doped porous carbon (Ru SAs/N-C) through a coordination-assisted strategy. This synthesis is based on the utilization of strong coordination between Ru3+ and the free amine groups (-NH2) at the skeleton of a metal-organic framework, which plays a critical role to access the atomically isolated dispersion of Ru sites. Without the assistance of the amino groups, the Ru precursor is prone to aggregation during the pyrolysis process, resulting in the formation of Ru clusters. The atomic dispersion of Ru on N-doped carbon can be verified by the spherical aberration correction electron microscopy and X-ray absorption fine structure measurements. Most importantly, this single Ru sites with single-mind N coordination can serve as a semihomogeneous catalyst to catalyze effectively chemoselective hydrogenation of functionalized quinolones.

Design of N-Coordinated Dual-Metal Sites: A Stable and Active Pt-Free Catalyst for Acidic Oxygen Reduction Reaction

We develop a host-guest strategy to construct an electrocatalyst with Fe-Co dual sites embedded on N-doped porous carbon and demonstrate its activity for oxygen reduction reaction in acidic electrolyte. Our catalyst exhibits superior oxygen reduction reaction performance, with comparable onset potential (Eonset, 1.06 vs 1.03 V) and half-wave potential (E1/2, 0.863 vs 0.858 V) than commercial Pt/C. The fuel cell test reveals (Fe,Co)/N-C outperforms most reported Pt-free catalysts in H2/O2 and H2/air. In addition, this cathode catalyst with dual metal sites is stable in a long-term operation with 50u202f000 cycles for electrode measurement and 100 h for H2/air single cell operation. Density functional theory calculations reveal the dual sites is favored for activation of O-O, crucial for four-electron oxygen reduction.

Ultrathin Palladium Nanomesh for Electrocatalysis

An ordered mesh of palladium with a thickness of about 3u2005nm was synthesized by a solution-based oxidative etching. The ultrathin palladium nanomeshes have an interconnected two-dimensional network of densely arrayed, ultrathin quasi-nanoribbons that form ordered open holes. The unique mesoporous structure and high specific surface area make these ultrathin Pd nanomeshes display superior catalytic performance for ethanol electrooxidation (mass activity of 5.40u2005Amu2009g-1 and specific activity of 7.09u2005mAu2009cm-2 at 0.8u2005V vs. RHE). Furthermore, the regular mesh structure can be applied to support other noble metals, such as platinum, which exhibits extremely high hydrogen evolution reaction (HER) activity and durability.

Efficient and Robust Hydrogen Evolution: Phosphorus Nitride Imide Nanotubes as Supports for Anchoring Single Ruthenium Sites.

Amorphous phosphorus nitride imide nanotubes (HPN) are reported as a novel substrate to stabilize materials containing single-metal sites. Abundant dangling unsaturated P vacancies play a role in stabilization. Ruthenium single atoms (SAs) are successfully anchored by strong coordination interactions between the d orbitals of Ru and the lone pair electrons of N located in the HPN matrix. The atomic dispersion of Ru atoms can be distinguished by X-ray absorption fine structure measurements and spherical aberration correction electron microscopy. Importantly, Ruu2005SAs@PN is an excellent electrocatalyst for the hydrogen evolution reaction (HER) in 0.5u2009m H2 SO4 , delivering a low overpotential of 24u2005mV at 10u2005mAu2009cm-2 and a Tafel slope of 38u2005mVu2009dec-1 . The catalyst exhibits robust stability in a constant current test at a large current density of 162u2005mAu2009cm-2 for more than 24u2005hours, and is operative for 5000 cycles in a cyclic voltammetry test. Additionally, Ruu2005SAs@PN presents a turnover frequency (TOF) of 1.67u2005H2 u2009s-1 at 25u2005mV, and 4.29u2005H2 u2009s-1 at 50u2005mV, in 0.5u2009m H2 SO4 solution, outperforming most of the reported hydrogen evolution catalysts. Density functional theory (DFT) calculations further demonstrate that the Gibbs free energy of adsorbed H* over the Ru SAs on PN is much closer to zero compared with the Ru/C and Ru SAs supported on carbon and C3 N4 , thus considerably facilitating the overall HER performance.

Direct transformation of bulk copper into copper single sites via emitting and trapping of atoms

AbstractSingle-atom catalysts exhibit intriguing properties and receive widespread interest for their effectiveness in promoting a variety of catalytic reactions, making them highly desired motifs in materials science. However, common approaches to the synthesis of these materials often require tedious procedures and lack appropriate interactions between the metal atoms and supports. Here, we report a simple and practical strategy to access the large-scale synthesis of single-atom catalysts via direct atoms emitting from bulk metals, and the subsequent trapping on nitrogen-rich porous carbon with the assistance of ammonia. First, the ammonia coordinates with the copper atoms to form volatile Cu(NH3)x species based on the strong Lewis acid–base interaction. Then, following transportation under an ammonia atmosphere, the Cu(NH3)x species are trapped by the defects on the nitrogen-rich carbon support, forming the isolated copper sites. This strategy is readily scalable and has been confirmed as feasible for producing functional single-atom catalysts at industrial levels.Single-atom catalysts have proven successful in many catalytic applications. Now, Li, Wu and co-workers show that single-atom catalysts can be prepared directly from bulk metals using an ammonia atmosphere, owing to the formation of volatile metal–ammonia species that are trapped by the nitrogen-rich carbon support.n

A single palladium site catalyst as a bridge for converting homogeneous to heterogeneous in dimerization of terminal aryl acetylenes

Herein, we utilize the surface dangling bond of MOFs as anchoring sites to access single Pd sites embedded on a hollow MOF nanobox. The stabilization of isolated Pd1 species is based on the strong coordination of the surface dangling bond of MOFs, followed by sequential reduction and phase transfer processes. The supported isolated single Pd sites can effect the highly active and selective process to produce conjugated dienes towards the dimerization of terminal aryl acetylenes, which has been previously only catalyzed by homogeneous catalysts. Unlike the commercial Pd/C and nanoparticles (NPs), the heterolytic cleavage of H2 and C–H bond efficient cleavage of terminal alkynes on atomically dispersed Pd1 sites ensure the high selectivity process and prevent the generation of styrene.

Pt9Ni Wavelike Nanowires with High Activity for Oxygen Reduction Reactions

Platinum (Pt)-based nanostructures are the most efficient catalysts for the oxygen reduction reaction (ORR) in acid media. Here, Pt9 Ni wavelike nanowires (W-NWs) have been synthesized by etching Pt3 Ni@PtNi2 core-shell nanowires with 2,5-dihydroxyterephthalic acid for 24u2005hours. Compared to the commercial Pt/C catalyst, the free-standing Pt9 Ni W-NWs show improvements of up to 9.3u2005times for mass activity and 12.6u2005times for specific activity, respectively.

Fabrication of Single-Atom Catalysts with Precise Structure and High Metal Loading

In recent years, single-atom catalysts (SACs) have attracted particular interest and have been demonstrated to be a promising material in energy conversion and chemical transformation due to their optimal atom utilization and unique size quantum effect. The development of a versatile and simple synthetic approach for SACs is important for further investigation of their properties. In this regard, several physical and chemical methods have been developed to access SACs by varying the interaction between metal centers and the coordination defects of the supports. The common challenges for SACs in industrial applications are accurate control over the local structure of single sites and increasing the active-site density. On one hand, the rational design of the atomic structure is decisive to their intrinsic activity, which will affect the adsorption and activation of reactants over the single sites. On the other hand, increasing the metal loading of SACs would largely enhance the density of active sites and the corresponding mass activity, especially for industrial applications. Here, approaches to the synthesis of SACs-focusing on these two challenges-are highlighted.

Mesoporous Pd@Ru Core–Shell Nanorods for Hydrogen Evolution Reaction in Alkaline Solution

The activity and stability of bimetallic nanocatalysts strongly depend on their structures, compositions, and interfaces. Here, we report the synthesis of mesoporous Pd@Ru core-shell bimetallic nanorods composed of face-centered cubic Pd and hexagonal close-packed Ru. The nanorods have two types of cavities with diameters of 3.0 ± 0.9 and 20.3 ± 8.1 nm. The mutual diffusion process between Ru and Pd is characterized by the high-angle annular dark-field scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy mapping, and the synchrotron radiation photoemission spectroscopy measurements. The mesoporous Pd@Ru nanorods exhibit superior catalytic performance and stability for hydrogen evolution reactions (overpotentials of 30 mV at 10 mA·cm-2 in 1.0 M KOH solution and 37 mV at 10 mA·cm-2 in 0.5 M H2SO4 solution).