Abstract
Rational design of the catalysts is impressive for sustainable energy conversion. However, there is a grand challenge to engineer active sites at the interface. Herein, hierarchical ...transition bimetal oxides/sulfides heterostructure arrays interacting two-dimensional MoO
x
/MoS
2
nanosheets attached to one-dimensional NiO
x
/Ni
3
S
2
nanorods were fabricated by oxidation/hydrogenation-induced surface reconfiguration strategy. The NiMoO
x
/NiMoS heterostructure array exhibits the overpotentials of 38 mV for hydrogen evolution and 186 mV for oxygen evolution at 10 mA cm
−2
, even surviving at a large current density of 500 mA cm
−2
with long-term stability. Due to optimized adsorption energies and accelerated water splitting kinetics by theory calculations, the assembled two-electrode cell delivers the industrially relevant current densities of 500 and 1000 mA cm
−2
at record low cell voltages of 1.60 and 1.66 V with excellent durability. This research provides a promising avenue to enhance the electrocatalytic performance of the catalysts by engineering interfacial active sites toward large-scale water splitting.
Abstract
Rational design of single atom catalyst is critical for efficient sustainable energy conversion. However, the atomic-level control of active sites is essential for electrocatalytic materials ...in alkaline electrolyte. Moreover, well-defined surface structures lead to in-depth understanding of catalytic mechanisms. Herein, we report a single-atomic-site ruthenium stabilized on defective nickel-iron layered double hydroxide nanosheets (Ru
1
/D-NiFe LDH). Under precise regulation of local coordination environments of catalytically active sites and the existence of the defects, Ru
1
/D-NiFe LDH delivers an ultralow overpotential of 18 mV at 10 mA cm
−2
for hydrogen evolution reaction, surpassing the commercial Pt/C catalyst. Density functional theory calculations reveal that Ru
1
/D-NiFe LDH optimizes the adsorption energies of intermediates for hydrogen evolution reaction and promotes the O–O coupling at a Ru–O active site for oxygen evolution reaction. The Ru
1
/D-NiFe LDH as an ideal model reveals superior water splitting performance with potential for the development of promising water-alkali electrocatalysts.
Rational design efficient transition metal-based electrocatalysts for oxygen evolution reaction (OER) is critical for water splitting. However, industrial water-alkali electrolysis requires large ...current densities at low overpotentials, always limited by intrinsic activity. Herein, we report hierarchical bimetal nitride/hydroxide (NiMoN/NiFe LDH) array as model catalyst, regulating the electronic states and tracking the relationship of structure-activity. As-activated NiMoN/NiFe LDH exhibits the industrially required current density of 1000 mA cm
at overpotential of 266 mV with 250 h stability for OER. Especially, in-situ electrochemical spectroscopic reveals that heterointerface facilitates dynamic structure evolution to optimize electronic structure. Operando electrochemical impedance spectroscopy implies accelerated OER kinetics and intermediate evolution due to fast charge transport. The OER mechanism is revealed by the combination of theoretical and experimental studies, indicating as-activated NiMoN/NiFe LDH follows lattice oxygen oxidation mechanism with accelerated kinetics. This work paves an avenue to develop efficient catalysts for industrial water electrolysis via tuning electronic states.
Using ab initio methods, we have investigated the structures and stabilities of Si(N) clusters (N ≤ 24) on Ag(111) surface as the initial stage of silicene growth. Unlike the dome-shaped graphene ...clusters, Si clusters prefer nearly flat structures with low buckling, more stable than directly deposition of the 3D freestanding Si clusters on Ag surface. The p-d hybridization between Ag and Si is revealed as well as sp(2) characteristics in Si(N)@Ag(111). Three types of silicene superstructures on Ag(111) surface have been considered and the simulated STM images are compared with experimental observations. Molecular dynamic simulations show high thermal stability of silicene on Ag(111) surfaces, contrast to that on Rh(111). The present theoretical results constitute a comprehensive picture about the interaction mechanism of silicene on Ag(111) surface and explain the superiority of Ag substrate for silicene growth, which would be helpful for improving the experimentally epitaxial growth of silicene.
Silicene, a two-dimensional hexagonal lattice of silicon, has been synthesized recently and exhibits fascinating electronic properties that resemble graphene. The substrate effect on the electronic ...properties of silicene is important for the practical applications of silicene. First-principles calculations were performed for silicene on two kinds of representative inert substrates, that is, hexagonal boron nitride (h-BN) monolayer and SiC(0001) surface. The silicene–substrate interaction energies range in 0.067–0.089 eV per Si atom, belonging to typical van der Waals interaction. The characteristic Dirac cone is preserved for silicene on h-BN monolayer or hydrogenated Si-terminated SiC(0001) surface. On the other hand, the silicene becomes metallic when it is placed on a hydrogenated C-terminated SiC(0001) surface. This effect was explained by the work functions for silicene and the substrates. The present results provide some guidelines for selecting proper substrates for silicene in future microelectronic devices.
As attractive analogue of graphene, boron monolayers have been theoretically predicted. However, due to electron deficiency of boron atom, synthesizing boron monolayer is very challenging in ...experiments. Using first-principles calculations, we explore stability and growth mechanism of various boron sheets on Cu(111) substrate. The monotonic decrease of formation energy of boron cluster B(N) with increasing cluster size and low diffusion barrier for a single B atom on Cu(111) surface ensure continuous growth of two-dimensional (2D) boron cluster. During growth process, hexagonal holes can easily arise at the edge of a 2D triangular boron cluster and then diffuse entad. Hence, large-scale boron monolayer with mixed hexagonal-triangular geometry can be obtained via either depositing boron atoms directly on Cu(111) surface or soft landing of small planar BN clusters. Our theoretical predictions would stimulate further experiments of synthesizing boron sheets on metal substrates and thus enrich the variety of 2D monolayer materials.
The structures of boron clusters, such as flat clusters and fullerenes, resemble those of carbon. Various two‐dimensional (2D) borophenes have been proposed since the production of graphene. The ...recent successful fabrication of borophene sheets has prompted extensive researches, and some unique properties are revealed. In this review, the recent theoretical and experimental progress on the structure, growth, and electronic and thermal transport properties of borophene sheets is summarized. The history of prediction of boron sheet structures is introduced. Existing with a mixture of triangle lattice and hexagonal lattice, the structures of boron sheets have peculiar characteristics of polymorphism and show significant dependence on the substrate. Due to the unique structure and complex BB bonds, borophene sheets have many interesting electronic and thermal transport properties, such as strong nonlinear effect, strong thermal transport anisotropy, high thermal conductance in the ballistic transport and low thermal conductivity in the diffusive transport. The growth mechanism and synthesis of borophene sheets on different metal substrates are also presented. The successful prediction and synthesis will shed light on the exploration of new novel materials. Besides, the outstanding and peculiar properties of borophene make them tempting platform for exploring novel physical phenomena and extensive applications.
The recent successful fabrication of borophene sheets has prompted extensive research. Here, the recent theoretical and experimental progress on the structure, growth, and electronic and thermal transport properties of borophene sheets is summarized. Recent theoretical studies on the thermal stability, ballistic thermal transport, diffusive thermal transport, and abnormal strain effect of borophene are discussed and compared with those of graphene.
China has made considerable efforts to mitigate the pollution of lakes over the past decade, but the success rate of these restoration actions at a national scale remains unclear. The present study ...compiled a 13-year (2005–2017) comprehensive dataset consisting of 24,319 records from China's 142 lakes and reservoirs. We developed a novel Water Quality Index (WQI-DET), customized to China's water quality classification scheme, to investigate the spatio-temporal pollution patterns. The likelihood of regime shifts during our study period is examined with a sequential algorithm. Our analysis suggests that China's lake water quality has improved and is also characterized by two WQI-DET abrupt shifts in 2007 and 2010. However, we also found that the eutrophication problems have not been eradicated and heavy metal (HM) pollution displayed an increasing trend. Our study suggests that the control of Cr, Cd and As should receive particular attention in an effort to alleviate the severity of HM pollution. Priority strategies to control HM pollution include the reduction of the contribution from mining activities and implementation of soil remediation in highly polluted areas. The mitigation efforts of lake eutrophication are more complicated due to the increasing importance of internal nutrient loading that can profoundly modulate the magnitude and timing of system response to external nutrient loading reduction strategies. We also contend that the development of a rigorous framework to quantify the socioeconomic benefits from well-functioning lake and reservoir ecosystems is critically important to gain leeway and keep the investments to the environment going, especially if the water quality improvements in many Chinese lakes and reservoirs are not realized in a timely manner.
Display omitted
•China's lake and reservoir water quality was investigated using a 13-year dataset.•China has been successful in improving water quality during the 2005–2017 period.•Eutrophication has been alleviated, but not fully eliminated until 2017.•Heavy metal (Cr, Cd, and As) pollution showed an increasing trend since 2012.
In vacuum, the bare zigzag (zz) edge of graphene is reconstructed into a line of pentagon–heptagon pairs, while the pristine armchair (ac) edge is retained. Our first-principle explorations of ...graphene edges on three metal surfaces Cu(111), Co(111), and Ni(111) indicate an opposite tendency, that is, the pristine zz edge is energetically favorable and the reconstructed ac edge with dangling C atoms is highly stable on Co(111) and Ni(111) surfaces. Insightful analysis shows that passivation of the graphene edge by metal surfaces is responsible for the dramatic differences. Beyond this, the unique edge configuration has a significant impact on the graphene CVD growth behavior.
Ultra-thin III-V semiconductors, which exhibit intriguing characteristics, such as two-dimensional (2D) electron gas, enhanced electron-hole interaction strength, and strongly polarized light ...emission, have always been anticipated in future electronics. However, their inherent strong covalent bonding in three dimensions hinders the layer-by-layer exfoliation, and even worse, impedes the 2D anisotropic growth. The synthesis of desirable ultra-thin III-V semiconductors is hence still in its infancy. Here we report the growth of a majority of ultra-thin III-V single crystals, ranging from ultra-narrow to wide bandgap semiconductors, through enhancing the interfacial interaction between the III-V crystals and the growth substrates to proceed the 2D layer-by-layer growth mode. The resultant ultra-thin single crystals exhibit fascinating properties of phonon frequency variation, bandgap shift, and giant second harmonic generation. Our strategy can provide an inspiration for synthesizing unexpected ultra-thin non-layered systems and also drive exploration of III-V semiconductor-based electronics.
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