Platinum-based catalysts have been considered the most effective electrocatalysts for the hydrogen evolution reaction in water splitting. However, platinum utilization in these electrocatalysts is ...extremely low, as the active sites are only located on the surface of the catalyst particles. Downsizing catalyst nanoparticles to single atoms is highly desirable to maximize their efficiency by utilizing nearly all platinum atoms. Here we report on a practical synthesis method to produce isolated single platinum atoms and clusters using the atomic layer deposition technique. The single platinum atom catalysts are investigated for the hydrogen evolution reaction, where they exhibit significantly enhanced catalytic activity (up to 37 times) and high stability in comparison with the state-of-the-art commercial platinum/carbon catalysts. The X-ray absorption fine structure and density functional theory analyses indicate that the partially unoccupied density of states of the platinum atoms' 5d orbitals on the nitrogen-doped graphene are responsible for the excellent performance.
Configuring metal single‐atom catalysts (SACs) with high electrocatalytic activity and stability is one efficient strategy in achieving the cost‐competitive catalyst for fuel cells’ applications. ...Herein, the atomic layer deposition (ALD) strategy for synthesis of Pt SACs on the metal–organic framework (MOF)‐derived N‐doped carbon (NC) is proposed. Through adjusting the ALD exposure time of the Pt precursor, the size‐controlled Pt catalysts, from Pt single atoms to subclusters and nanoparticles, are prepared on MOF‐NC support. X‐ray absorption fine structure spectra determine the increased electron vacancy in Pt SACs and indicate the Pt–N coordination in the as‐prepared Pt SACs. Benefiting from the low‐coordination environment and anchoring interaction between Pt atoms and nitrogen‐doping sites from MOF‐NC support, the Pt SACs deliver an enhanced activity and stability with 6.5 times higher mass activity than that of Pt nanoparticle catalysts in boosting the oxygen reduction reaction (ORR). Density functional theory calculations indicate that Pt single atoms prefer to be anchored by the pyridinic N‐doped carbon sites. Importantly, it is revealed that the electronic structure of Pt SAs can be adjusted by adsorption of hydroxyl and oxygen, which greatly lowers free energy change for the rate‐determining step and enhances the activity of Pt SACs toward the ORR.
The atomic layer deposition (ALD) strategy for synthesis of Pt single‐atom catalysts (SACs) on the metal–organic framework (MOF)‐derived N‐doped carbon (NC) is proposed. Benefiting from the low‐coordination environment and anchoring interaction between Pt atoms and nitrogen‐doping sites from MOF‐NC support, the ALDPt SACs deliver an enhanced activity and stability in boosting the oxygen reduction reaction (ORR).
This book explores the roles of agricultural development and advancing social complexity in the processes of state formation in China. Over a period of about 10,000 years, it follows evolutionary ...trajectories of society from the last Palaeolithic hunting-gathering groups, through Neolithic farming villages and on to the Bronze Age Shang dynasty in the latter half of the second millennium BC. Li Liu and Xingcan Chen demonstrate that sociopolitical evolution was multicentric and shaped by inter-polity factionalism and competition, as well as by the many material technologies introduced from other parts of the world. The book illustrates how ancient Chinese societies were transformed during this period from simple to complex, tribal to urban, and preliterate to literate.
Elemental 2D materials with fascinating characteristics are regarded as an influential portion of the 2D family. Iodine is as a typical monoelemental molecular crystal and exhibits great prospects of ...applications. To realize 2D iodine, not only is it required to separate the weak interlayer van der Waals interactions, but also to reserve the weak intramolecular halogen bonds; thus, 2D iodine is still unexploited until now. Herein, atomically thin iodine nanosheets (termed “iodinene”) with the thickness around 1.0 nm and lateral sizes up to hundreds of nanometers are successfully fabricated by a liquid‐phase exfoliation strategy. When used for the cathode of rechargeable sodium‐ion batteries, the ultrathin iodinene exhibits superb rate properties with a high specific capacity of 109.5 mA h g−1 at the high rate of 10 A g−1 owing to its unique 2D ultrathin architecture with remarkably enhanced pseudocapacitive behavior. First‐principles calculations reveal that the diffusion of sodium ions in few‐layered iodinene changes from the original horizontal direction in bulk to the vertical with a small energy barrier of 0.07 eV because of the size effect. The successful preparation and intensive structural investigation of iodinene paves the way for the development of novel iodine‐based science and technologies.
Atomically thin iodinene nanosheets are successfully fabricated by a liquid‐phase exfoliation strategy. When explored as cathodes for Na+‐ion batteries, they exhibit a high specific capacity and an extraordinary rate performance owing to their unique 2D ultrathin architecture with largely lower energy barrier and totally different ion‐diffusion path versus the bulk counterpart.
Despite the increasing resolution, forcing on the mean circulation by resolved waves in general circulation models is not yet converging. Parameterization of the forcing remains a major source of ...model uncertainty. This study examines the scale invariance of zonal spectra of momentum flux and wave forcing, and shows that it can be used to quantify the forcing by unresolved waves with knowledge of the resolved ones in global models. The result reveals the leading order importance of the small-scale wave forcing, which is in general agreement with that required for obtaining the zonal mean wind climatology. It is also found that wave and mean flow interaction is important in maintaining the robust spectral structure. This method may provide a strategy to design physically consistent and scale-aware parameterization schemes for scale invariant quantities, when a model has sufficient resolution to partially resolve their spectra.
Phosphorene, also known as single- or few-layer black phosphorus (FLBP), is a new member of the two-dimensional (2D) material family and has attracted significant attention in recent years for ...applications in optoelectronics, energy storage and biomedicine due to its unique physicochemical properties and excellent biocompatibility. FLBP is regarded as a potential biological imaging agent for cancer diagnosis due to its intrinsic fluorescence (FL) and photoacoustic (PA) properties and negligible cytotoxicity. FLBP-based photothermal and photodynamic therapies have emerged with excellent anti-tumour therapeutic efficacies due to their unique physical properties, such as near-infrared (NIR) optical absorbance, large extinction coefficients, biodegradability and reactive oxygen species (ROS) or heat generation upon light irradiation. Furthermore, FLBP is a promising drug delivery platform because of its high drug-loading capacity due to its puckered layer structure with an ultralarge surface area, and FLBP is size-controllable with facile surface chemical modification. Because of the marked advantages of FLBP nanomaterials in biomedical applications, an overview of the latest progress and paradigms of FLBP-based nanoplatforms for multidisciplinary biomedical applications is presented in this tutorial review.
Abstract
As one of the most important photocatalysts, TiO
2
has triggered broad interest and intensive studies for decades. Observation of the interfacial reactions between water and TiO
2
at ...microscopic scale can provide key insight into the mechanisms of photocatalytic processes. Currently, experimental methodologies for characterizing photocatalytic reactions of anatase TiO
2
are mostly confined to water vapor or single molecule chemistry. Here, we investigate the photocatalytic reaction of anatase TiO
2
nanoparticles in water using liquid environmental transmission electron microscopy. A self-hydrogenated shell is observed on the TiO
2
surface before the generation of hydrogen bubbles. First-principles calculations suggest that this shell is formed through subsurface diffusion of photo-reduced water protons generated at the aqueous TiO
2
interface, which promotes photocatalytic hydrogen evolution by reducing the activation barrier for H
2
(H–H bond) formation. Experiments confirm that the self-hydrogenated shell contains reduced titanium ions, and its thickness can increase to several nanometers with increasing UV illuminance.
Background： The prognostic values of staging parameters require continual re-assessment amid changes in diag-nostic and therapeutic methods. This study aimed to identify the prognostic factors and ...failure patterns of non-meta-static nasopharyngeal carcinoma（NPC） in the intensity-modulated radiotherapy（IMRT） era.Methods： We reviewed the data from 749 patients with newly diagnosed, biopsy-proven, non-metastatic NPC in our cancer center（South China, an NPC endemic area） between January 2003 and December 2007. All patients under-went magnetic resonance imaging（MRI） before receiving IMRT. The actuarial survival rates were estimated using the Kaplan–Meier method, and survival curves were compared using the log-rank test. Multivariate analyses with the Cox proportional hazards model were used to test for the independent prognostic factors by backward eliminating insigniicant explanatory variables.Results： The 5-year occurrence rates of local failure, regional failure, locoregional failure, and distant failure were 5.4, 3.0, 7.4, and 17.4%, respectively. The 5-year survival rates were as follows： local relapse-free survival, 94.6%; nodal relapse-free survival, 97.0%; distant metastasis-free survival, 82.6%; disease-free survival, 75.1%; and overall survival, 82.0%. Multivariate Cox regression analysis revealed that orbit involvement was the only signiicant prognostic fac-tor for local failure（P = 0.011）. Parapharyngeal tumor extension, retropharyngeal lymph node involvement, and the laterality, longest diameter, and Ho＇s location of the cervical lymph nodes were signiicant prognostic factors for both distant failure and disease failure（all P 〈 0.05）. Intracranial extension had signiicant prognostic value for distant failure（P = 0.040）.Conclusions： The key failure pattern for NPC was distant metastasis in the IMRT era. With changes in diagnostic and therapeutic technologies as well as treatment modalities, the signiicant prognostic parameters for local control have also been altered substantially.
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