The Power of Single-Atom Catalysis Liang, Suxia; Hao, Ce; Shi, Yantao
ChemCatChem,
September 1, 2015, Letnik:
7, Številka:
17
Journal Article
Recenzirano
Single‐atom catalysts (SACs) with individual and isolated metal atoms anchored to supports can act as active centers. Single‐atom catalysis is powerful and attractive because SACs have demonstrated ...distinguishing performances, such as drastic cost‐reduction, notable catalytic activity, and selectivity. Herein, we firstly introduce SAC, including the concept and some key issues in synthesis and catalysis. Then, the power of single‐atom catalysis is highlighted and the most recent advances are summarized. It is very encouraging that in recent years our understanding of SACs has increased, owing to substantial studies regarding sample preparation, characterization, evaluation, and also mechanistic interpretation. On the other hand, great challenges still remain for SACs.
Single and ready to mingle: Single‐atom catalysts (SACs) with individual and isolated metal atoms anchored to supports can act as active centers. Single‐atom catalysis is powerful and attractive because SACs have demonstrated exceptional performance, such as drastic cost‐reduction, notable catalytic activity, and selectivity. SMSI=Strong metal–support interaction.
The path planning for high-speed unmanned surface vehicle raises more complicated requirements to reduce sailing time and save energy. In this article, a new predictive artificial potential field is ...proposed using time information and predictive potential to plan a smoother path. The principle of artificial potential field with vehicle dynamics and reachability in local minimum is studied. According to global and local path planning, the most state-of-the-art traditional artificial potential field and its drawback are analysed at first. Then we proposed predictive artificial potential field with three modifications: angle limit, velocity adjustment and predictive potential to improve the feasibility and flatness of the generated path. In addition, we compare the performance between traditional artificial potential field and predictive artificial potential field, where predictive artificial potential field successfully restricts the maximum turning angle, cuts short sailing time and intelligently avoids obstacle. From the simulation results, we also verify that predictive artificial potential field can solve concave local minimum problem and enhance the reachability in special scenario. Therefore, the more reasonable path generated by predictive artificial potential field reduces sailing time and helps conserve more energy for unmanned surface vehicle.
Inside a liquid solution, oriented attachment (OA) is now recognized to be as important a pathway to crystal growth as other, more conventional growth mechanisms. However, the driving force that ...controls the occurrence of OA is still poorly understood. Here, using in-situ liquid cell transmission electron microscopy, we demonstrate the ligand-controlled OA of citrate-stabilized gold nanoparticles at atomic resolution. Our data reveal that particle pairs rotate randomly at a separation distance greater than twice the layer thickness of adsorbed ligands. In contrast, when the particles get closer, their ligands overlap and guide the rotation into a directional mode until they share a common {111} orientation, when a sudden contact occurs accompanied by the simultaneous expulsion of the ligands on this surface. First-principle calculations confirm that the lower ligand binding energy on {111} surfaces is the intrinsic reason for the preferential attachment at this facet, rather than on other low-index facets.
Inorganic electron‐selective layers (ESLs) are fabricated at extremely low temperatures of 70 °C or even 25 °C by a simple solution route. This is of great significance because the attained PCEs ...confirm the feasibility of room‐temperature coating of inorganic amorphous ESLs through a solution method for the first time.
The electronically excited state and luminescence property of metal–organic framework MOF-5 were investigated using relativistic density functional theory (DFT) and time-dependent DFT (TDDFT). The ...geometry, IR spectra, and UV–vis spectra of MOF-5 in the ground state were calculated using relativistic DFT, leading to good agreement between the experimental and theoretical results. The frontier molecular orbitals and electronic configuration indicated that the luminescence mechanism in MOF-5 follows ligand-to-ligand charge transfer (LLCT), namely, π* → π, rather than emission with the ZnO quantum dot (QD) proposed by Bordiga et al. The geometry and IR spectra of MOF-5 in the electronically excited state have been calculated using the relativistic TDDFT and compared with those for the ground state. The comparison reveals that the Zn4O13 QD is rigid, whereas the ligands BDC2– are nonrigid. In addition, the calculated emission band of MOF-5 is in good agreement with the experimental result and is similar to that of the ligand H2BDC. The combined results confirmed that the luminescence mechanism for MOF-5 should be LLCT with little mixing of the ligand-to-metal charge transfer. The reason for the MOF-5 luminescence is explained by the excellent coplanarity between the six-membered ring consisting of zinc, oxygen, carbon, and the benzene ring.
Solar-to-electricity conversion efficiency, power conversion efficiency (PCE), and stability are two important aspects of perovskite solar cells (PSCs). However, both aspects are difficult to ...simultaneously enhance. In the recent two years, two-dimensional (2D)/three-dimensional (3D) stacking structure, designed by covering the 3D perovskite with a thin 2D perovskite capping layer, was reported to be a promising method to achieve both a higher PCE and improved stability simultaneously. However, when reducing the surface defects of 3D perovskite, the thin 2D capping layer itself may probably introduce additional interfacial defects in a 2D/3D stacking structure, which is thought to be able to trigger trap-assisted nonradiative recombination or ion migration. Thus, efforts should be paid to reduce the interfacial defects of 2D hybrid perovskite when serving as a modification layer in a 2D/3D stacking structure PSCs. Here, we demonstrate that bromine (Br) doping of the 2D perovskite capping layer is an efficient strategy to passivate interfacial defects robustly, by which the photoluminescence lifetime is enhanced notably, whereas the interfacial charge recombination is suppressed a lot. As a result, the PCE is enhanced from 18.01% (3D perovskite) to 20.07% (Br-doped 2D/3D perovskite) along with improved moisture stability.
Sulfamethoxypyridazine（SMP） is one of the commonly used sulfonamide antibiotics（SAs）.SAs are mainly studied to undergo triplet-sensitized photodegradation in water under natural sunlight with other ...coexisting aquatic environmental organic pollutants.In this work,SMP was selected as a representative of SAs.We studied the mechanisms of triplet-sensitized photodegradation of SMP and the influence of selected dissolved inorganic matter,i.e.,anions（Br~-,Cl~-,and NO~-_3） and cations ions（Ca~（2＋）,Mg~（2＋）,and Zn~（2＋）） on SMP photodegradation mechanism by quantum chemical methods.In addition,the degradation mechanisms of SMP by hydroxyl radical（OH·） were also investigated.The creation of SO_2 extrusion product was accessed with two different energy pathways（pathway-1 and pathway-2） by following two steps（step-I and step-II） in the tripletsensitized photodegradation of SMP.Due to low activation energy,the pathway-1 was considered as the main pathway to obtain SO_2 extrusion product.Step-II of pathway-1 was measured to be the rate-limiting step（RLS） of SMP photodegradation mechanism and the effect of the selected anions and cations was estimated for this step.All selected anions and cations promoted photodegradation of SMP by dropping the activation energy of pathway-1.The estimated low activation energies of different degradation pathways of SMP with OH·radical indicate that OH·radical is a very powerful oxidizing agent for SMP degradation via attack through benzene derivative and pyridazine derivative ring.
A theoretical investigation of hydroxide ion transport mechanism in quaternary ammonium functionalized polystyrene (QAPS) anion exchange membrane (AEM) was studied by density functional theory (DFT). ...The results showed that there were two steps for OH− transferring through QAPS-AEM. The first step was the movement of OH− in water channel, which was induced by frequently forming and breaking of hydrogen bonds (H-bonds) between H2O and OH−. The second step was that OH− transferred across the quaternary ammonium (QA) groups by following the rotation about CC single bond, which was the rate-determining step for OH− transferring in QAPS-AEM. We presented that the ionic groups on the side chain of polymer with smaller space steric should provide higher ion conductivity due to their lower rotation energy barriers.
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•The OH− transport mechanism in quaternary ammonium functionalized polystyrene was studied by DFT.•There were two steps in the OH− transport process in anion exchange membrane.•The role of hydrogen bonding was investigated by DFT.•The rotation about ionic groups was studied in detail during OH− transport.
A high performance of anion exchange membranes (AEMs) is highly demanded in anion exchange membrane fuel cells (AEMFCs) and has been extensively studied. However, the poor ionic conductivities and ...the alkaline stability might limit their applications. Herein, we developed a novel strategy to improve the ionic conductivity and alkaline stability of AEMs by introducing hydrophilic oligo(ethylene glycol)(OEG) groups. Continuous ion-conducting channels were efficiently formed thanks to the dynamic aggregation of water molecules assisted by the hydrophilic side chains. The resultant AEMs with low IEC values showed significant enhancement in hydroxide conductivity compared to the AEMs functionalized by the conventional 1,2-dimethylimidazolium (PSf-Im), as the hydroxide conductivity of PSf-2 membrane with an IEC of 1.05 mmol g−1 was 59.5 mS·cm−1 at 60 °C while the hydroxide conductivity of PSf-Im membrane with an IEC of 1.27 mmol g−1 was 36.7 mS·cm−1. In addition, the alkaline stability and the mechanical properties of the resultant AEMs were improved remarkably. The density functional theory (DFT) study showed that the introduction of OEG part can significantly increase the LUMO energy of functional group and then enhance the alkaline stability.
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•Continuous ion-conducting channels were efficiently formed.•The dynamic aggregation of water molecules was assisted by the hydrophilic side chains.•An enhancement in water uptake and hydroxide conductivity of the resultant AEMs.•The alkaline stability and mechanical properties were also improved.
Impeding high temperature sintering is challengeable for synthesis of carbon-supported single-atom catalysts (C-SACs), which requires high-cost precursor and strictly-controlled procedures. Herein, ...by virtue of the ultrastrong polarity of salt melts, sintering of metal atoms is effectively suppressed. Meanwhile, doping with inorganic sulfur anions not only produces sufficient anchoring sites to achieve high loading of atomically dispersed Co up to 13.85 wt.%, but also enables their electronic and geometric structures to be well tuned. When served as a cathode catalyst in dye-sensitized solar cells, the C-SAC with Co-N
4
-S
2
moieties exhibits high activity towards the iodide reduction reaction (IRR), achieving a higher power conversion efficiency than that of conventional Pt counterpart. Density function theory (DFT) calculations revealed that the superior IRR activity was ascribed to the unique structure of Co-N
4
-S
2
moieties with lower reaction barriers and moderate binding energy of iodine on the Co center, which was beneficial to I
2
dissociation.
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