Showing papers by "University of Science and Technology of China published in 2018"

Gate-tunable room-temperature ferromagnetism in two-dimensional Fe 3 GeTe 2 .

Abstract: Materials research has driven the development of modern nano-electronic devices. In particular, research in magnetic thin films has revolutionized the development of spintronic devices1,2 because identifying new magnetic materials is key to better device performance and design. Van der Waals crystals retain their chemical stability and structural integrity down to the monolayer and, being atomically thin, are readily tuned by various kinds of gate modulation3,4. Recent experiments have demonstrated that it is possible to obtain two-dimensional ferromagnetic order in insulating Cr2Ge2Te6 (ref. 5) and CrI3 (ref. 6) at low temperatures. Here we develop a device fabrication technique and isolate monolayers from the layered metallic magnet Fe3GeTe2 to study magnetotransport. We find that the itinerant ferromagnetism persists in Fe3GeTe2 down to the monolayer with an out-of-plane magnetocrystalline anisotropy. The ferromagnetic transition temperature, Tc, is suppressed relative to the bulk Tc of 205 kelvin in pristine Fe3GeTe2 thin flakes. An ionic gate, however, raises Tc to room temperature, much higher than the bulk Tc. The gate-tunable room-temperature ferromagnetism in two-dimensional Fe3GeTe2 opens up opportunities for potential voltage-controlled magnetoelectronics7-11 based on atomically thin van der Waals crystals.

Metal-Organic Frameworks as Platforms for Catalytic Applications.

Abstract: Metal-organic frameworks (MOFs), also called porous coordination polymers, represent a class of crystalline porous materials built from organic linkers and metal ions/clusters. The unique features of MOFs, including structural diversity and tailorability as well as high surface area, etc., enable them to be a highly versatile platform for potential applications in many fields. Herein, an overview of recent developments achieved in MOF catalysis, including heterogeneous catalysis, photocatalysis, and eletrocatalysis over MOFs and MOF-based materials, is provided. The active sites involved in the catalysts are particularly emphasized. The challenges, future trends, and prospects associated with MOFs and their related materials for catalysis are also discussed.

A Survey on Learning to Hash

Abstract: Nearest neighbor search is a problem of finding the data points from the database such that the distances from them to the query point are the smallest. Learning to hash is one of the major solutions to this problem and has been widely studied recently. In this paper, we present a comprehensive survey of the learning to hash algorithms, categorize them according to the manners of preserving the similarities into: pairwise similarity preserving, multiwise similarity preserving, implicit similarity preserving, as well as quantization, and discuss their relations. We separate quantization from pairwise similarity preserving as the objective function is very different though quantization, as we show, can be derived from preserving the pairwise similarities. In addition, we present the evaluation protocols, and the general performance analysis, and point out that the quantization algorithms perform superiorly in terms of search accuracy, search time cost, and space cost. Finally, we introduce a few emerging topics.

Regulation of Coordination Number over Single Co Sites: Triggering the Efficient Electroreduction of CO2.

Abstract: The design of active, selective, and stable CO2 reduction electrocatalysts is still challenging. A series of atomically dispersed Co catalysts with different nitrogen coordination numbers were prepared and their CO2 electroreduction catalytic performance was explored. The best catalyst, atomically dispersed Co with two-coordinate nitrogen atoms, achieves both high selectivity and superior activity with 94 % CO formation Faradaic efficiency and a current density of 18.1 mA cm-2 at an overpotential of 520 mV. The CO formation turnover frequency reaches a record value of 18 200 h-1 , surpassing most reported metal-based catalysts under comparable conditions. Our experimental and theoretical results demonstrate that lower a coordination number facilitates activation of CO2 to the CO2.- intermediate and hence enhances CO2 electroreduction activity.

Isolated Ni single atoms in graphene nanosheets for high-performance CO2 reduction

Abstract: Single-atom catalysts have emerged as an exciting paradigm with intriguing properties different from their nanocrystal counterparts Here we report Ni single atoms dispersed into graphene nanosheets, without Ni nanoparticles involved, as active sites for the electrocatalytic CO2 reduction reaction (CO2RR) to CO While Ni metal catalyzes the hydrogen evolution reaction (HER) exclusively under CO2RR conditions, Ni single atomic sites present a high CO selectivity of 95% under an overpotential of 550 mV in water, and an excellent stability over 20 hours’ continuous electrolysis The current density can be scaled up to more than 50 mA cm−2 with a CO evolution turnover frequency of 21 × 105 h−1 while maintaining 97% CO selectivity using an anion membrane electrode assembly Different Ni sites in graphene vacancies, with or without neighboring N coordination, were identified by in situ X-ray absorption spectroscopy and density functional theory calculations Theoretical analysis of Ni and Co sites suggests completely different reaction pathways towards the CO2RR or HER, in agreement with experimental observations

Achieving a Record-High Yield Rate of 120.9 μgNH3 mgcat.-1 h-1 for N2 Electrochemical Reduction over Ru Single-Atom Catalysts.

Abstract: The electrochemical reduction of N2 into NH3 production under ambient conditions represents an attractive prospect for the fixation of N2 . However, this process suffers from low yield rate of NH3 over reported electrocatalysts. In this work, a record-high activity for N2 electrochemical reduction over Ru single atoms distributed on nitrogen-doped carbon (Ru SAs/N-C) is reported. At -0.2 V versus reversible hydrogen electrode, Ru SAs/N-C achieves a Faradaic efficiency of 29.6% for NH3 production with partial current density of -0.13 mA cm-2 . Notably, the yield rate of Ru SAs/N-C reaches 120.9 μgNH3 mgcat.-1 h-1, which is one order of magnitude higher than the highest value ever reported. This work not only develops a superior electrocatalyst for NH3 production, but also provides a guideline for the rational design of highly active and robust single-atom catalysts.

Stable cycling of high-voltage lithium metal batteries in ether electrolytes

Abstract: The key to enabling long-term cycling stability of high-voltage lithium (Li) metal batteries is the development of functional electrolytes that are stable against both Li anodes and high-voltage (above 4 V versus Li/Li+) cathodes. Due to their limited oxidative stability ( 90% over 300 cycles and ~80% over 500 cycles with a charge cut-off voltage of 4.3 V. This study offers a promising approach to enable ether-based electrolytes for high-voltage Li metal battery applications. Ether-based electrolytes offer many advantages compared to other electrolyte systems, but they are not stable in Li metal batteries when operating at high voltages. Here, the authors develop a concentrated ether electrolyte that enables long-term cycling stability of high-voltage Li metal batteries.

Defect Effects on TiO2 Nanosheets: Stabilizing Single Atomic Site Au and Promoting Catalytic Properties.

Abstract: Isolated single atomic site catalysts have attracted great interest due to their remarkable catalytic properties Because of their high surface energy, single atoms are highly mobile and tend to form aggregate during synthetic and catalytic processes Therefore, it is a significant challenge to fabricate isolated single atomic site catalysts with good stability Herein, a gentle method to stabilize single atomic site metal by constructing defects on the surface of supports is presented As a proof of concept, single atomic site Au supported on defective TiO2 nanosheets is prepared and it is discovered that (1) the surface defects on TiO2 nanosheets can effectively stabilize Au single atomic sites through forming the Ti-Au-Ti structure; and (2) the Ti-Au-Ti structure can also promote the catalytic properties through reducing the energy barrier and relieving the competitive adsorption on isolated Au atomic sites It is believed that this work paves a way to design stable and active single atomic site catalysts on oxide supports

Tailoring the d-Band Centers Enables Co4N Nanosheets To Be Highly Active for Hydrogen Evolution Catalysis

Abstract: Endowing materials with specific functions that are not readily available is always of great importance, but extremely challenging. Co4 N, with its beneficial metallic characteristics, has been proved to be highly active for the oxidation of water, while it is notoriously poor for catalyzing the hydrogen evolution reaction (HER), because of its unfavorable d-band energy level. Herein, we successfully endow Co4 N with prominent HER catalytic capability by tailoring the positions of the d-band center through transition-metal doping. The V-doped Co4 N nanosheets display an overpotential of 37 mV at 10 mA cm-2 , which is substantially better than Co4 N and even close to the benchmark Pt/C catalysts. XANES, UPS, and DFT calculations consistently reveal the enhanced performance is attributed to the downshift of the d-band center, which helps facilitate the H desorption. This concept could provide valuable insights into the design of other catalysts for HER and beyond.

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

Abstract: Single-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.

Blockade of the checkpoint receptor TIGIT prevents NK cell exhaustion and elicits potent anti-tumor immunity.

Abstract: Checkpoint blockade enhances effector T cell function and has elicited long-term remission in a subset of patients with a broad spectrum of cancers. TIGIT is a checkpoint receptor thought to be involved in mediating T cell exhaustion in tumors; however, the relevance of TIGIT to the dysfunction of natural killer (NK) cells remains poorly understood. Here we found that TIGIT, but not the other checkpoint molecules CTLA-4 and PD-1, was associated with NK cell exhaustion in tumor-bearing mice and patients with colon cancer. Blockade of TIGIT prevented NK cell exhaustion and promoted NK cell-dependent tumor immunity in several tumor-bearing mouse models. Furthermore, blockade of TIGIT resulted in potent tumor-specific T cell immunity in an NK cell-dependent manner, enhanced therapy with antibody to the PD-1 ligand PD-L1 and sustained memory immunity in tumor re-challenge models. This work demonstrates that TIGIT constitutes a previously unappreciated checkpoint in NK cells and that targeting TIGIT alone or in combination with other checkpoint receptors is a promising anti-cancer therapeutic strategy.

Refining Defect States in W18O49 by Mo Doping: A Strategy for Tuning N2 Activation towards Solar-Driven Nitrogen Fixation.

Abstract: Photocatalysis may provide an intriguing approach to nitrogen fixation, which relies on the transfer of photoexcited electrons to the ultrastable N≡N bond. Upon N2 chemisorption at active sites (e.g., surface defects), the N2 molecules have yet to receive energetic electrons toward efficient activation and dissociation, often forming a bottleneck. Herein, we report that the bottleneck can be well tackled by refining the defect states in photocatalysts via doping. As a proof of concept, W18O49 ultrathin nanowires are employed as a model material for subtle Mo doping, in which the coordinatively unsaturated (CUS) metal atoms with oxygen defects serve as the sites for N2 chemisorption and electron transfer. The doped low-valence Mo species play multiple roles in facilitating N2 activation and dissociation by refining the defect states of W18O49: (1) polarizing the chemisorbed N2 molecules and facilitating the electron transfer from CUS sites to N2 adsorbates, which enables the N≡N bond to be more feasible fo...

From Metal–Organic Frameworks to Single-Atom Fe Implanted N-doped Porous Carbons: Efficient Oxygen Reduction in Both Alkaline and Acidic Media

Abstract: It remains highly desired but a great challenge to achieve atomically dispersed metals in high loadings for efficient catalysis. Now porphyrinic metal-organic frameworks (MOFs) have been synthesized based on a novel mixed-ligand strategy to afford high-content (1.76 wt %) single-atom (SA) iron-implanted N-doped porous carbon (FeSA -N-C) via pyrolysis. Thanks to the single-atom Fe sites, hierarchical pores, oriented mesochannels and high conductivity, the optimized FeSA -N-C exhibits excellent oxygen reduction activity and stability, surpassing almost all non-noble-metal catalysts and state-of-the-art Pt/C, in both alkaline and more challenging acidic media. More far-reaching, this MOF-based mixed-ligand strategy opens a novel avenue to the precise fabrication of efficient single-atom catalysts.

Oxygen-Vacancy-Mediated Exciton Dissociation in BiOBr for Boosting Charge-Carrier-Involved Molecular Oxygen Activation

Abstract: Excitonic effects mediated by Coulomb interactions between photogenerated electrons and holes play crucial roles in photoinduced processes of semiconductors. In terms of photocatalysis, however, efforts have seldom been devoted to the relevant aspects. For the catalysts with giant excitonic effects, the coexisting, competitive exciton generation serves as a key obstacle to the yield of free charge carriers, and hence, transformation of excitons into free carriers would be beneficial for optimizing the charge-carrier-involved photocatalytic processes. Herein, by taking bismuth oxybromide (BiOBr) as a prototypical model system, we demonstrate that excitons can be effectively dissociated into charge carriers with the incorporation of oxygen vacancy, leading to excellent performances in charge-carrier-involved photocatalytic reactions such as superoxide generation and selective organic syntheses under visible-light illumination. This work not only establishes an in-depth understanding of defective structures ...

Atomic-level insight into super-efficient electrocatalytic oxygen evolution on iron and vanadium co-doped nickel (oxy)hydroxide.

Abstract: It is of great importance to understand the origin of high oxygen-evolving activity of state-of-the-art multimetal oxides/(oxy)hydroxides at atomic level. Herein we report an evident improvement of oxygen evolution reaction activity via incorporating iron and vanadium into nickel hydroxide lattices. X-ray photoelectron/absorption spectroscopies reveal the synergistic interaction between iron/vanadium dopants and nickel in the host matrix, which subtly modulates local coordination environments and electronic structures of the iron/vanadium/nickel cations. Further, in-situ X-ray absorption spectroscopic analyses manifest contraction of metal-oxygen bond lengths in the activated catalyst, with a short vanadium-oxygen bond distance. Density functional theory calculations indicate that the vanadium site of the iron/vanadium co-doped nickel (oxy)hydroxide gives near-optimal binding energies of oxygen evolution reaction intermediates and has lower overpotential compared with nickel and iron sites. These findings suggest that the doped vanadium with distorted geometric and disturbed electronic structures makes crucial contribution to high activity of the trimetallic catalyst.

Satellite-Relayed Intercontinental Quantum Network.

Abstract: We perform decoy-state quantum key distribution between a low-Earth-orbit satellite and multiple ground stations located in Xinglong, Nanshan, and Graz, which establish satellite-to-ground secure keys with similar to kHz rate per passage of the satellite Micius over a ground station. The satellite thus establishes a secure key between itself and, say, Xinglong, and another key between itself and, say, Graz. Then, upon request from the ground command, Micius acts as a trusted relay. It performs bitwise exclusive OR operations between the two keys and relays the result to one of the ground stations. That way, a secret key is created between China and Europe at locations separated by 7600 km on Earth. These keys are then used for intercontinental quantum-secured communication. This was, on the one hand, the transmission of images in a one-time pad configuration from China to Austria as well as from Austria to China. Also, a video conference was performed between the Austrian Academy of Sciences and the Chinese Academy of Sciences, which also included a 280 km optical ground connection between Xinglong and Beijing. Our work clearly confirms the Micius satellite as a robust platform for quantum key distribution with different ground stations on Earth, and points towards an efficient solution for an ultralong-distance global quantum network.

A hydrogel-based antifouling solar evaporator for highly efficient water desalination

Abstract: Solar desalination is a promising method for large-scale water purification by utilizing sustainable energy. However, current high-rate solar evaporation often relies on optical concentration due to the diffusion of natural sunlight, which leads to inadequate energy supply. Here we demonstrate a hydrogel-based solar evaporator that is capable of generating vapor at a high rate of ∼2.5 kg m−2 h−1 under one sun irradiation (1 kW m−2), among the best values reported in the literature. Such highly efficient solar evaporation is achieved by a hybrid hydrogel composed of a hydrophilic polymer framework (polyvinyl alcohol, PVA) and solar absorber (reduced graphene oxide, rGO), which has internal capillary channels. The PVA can greatly facilitate the water evaporation owing to the reduced water evaporation enthalpy in the hydrogel network. The rGO penetrating into the polymeric network enables efficient energy utilization. The capillary channels sustain an adequate water supply for continuous solar vapor generation at a high rate. This hydrogel-based solar evaporator also exhibits promising antifouling properties, enabling long-term water desalination without recycling. The high-efficiency hydrogel-based solar vapor generators open significant opportunities to enhance solar water evaporation performance and reduce the cost of solar desalination systems.

xDeepFM: Combining Explicit and Implicit Feature Interactions for Recommender Systems

Abstract: Combinatorial features are essential for the success of many commercial models. Manually crafting these features usually comes with high cost due to the variety, volume and velocity of raw data in web-scale systems. Factorization based models, which measure interactions in terms of vector product, can learn patterns of combinatorial features automatically and generalize to unseen features as well. With the great success of deep neural networks (DNNs) in various fields, recently researchers have proposed several DNN-based factorization model to learn both low- and high-order feature interactions. Despite the powerful ability of learning an arbitrary function from data, plain DNNs generate feature interactions implicitly and at the bit-wise level. In this paper, we propose a novel Compressed Interaction Network (CIN), which aims to generate feature interactions in an explicit fashion and at the vector-wise level. We show that the CIN share some functionalities with convolutional neural networks (CNNs) and recurrent neural networks (RNNs). We further combine a CIN and a classical DNN into one unified model, and named this new model eXtreme Deep Factorization Machine (xDeepFM). On one hand, the xDeepFM is able to learn certain bounded-degree feature interactions explicitly; on the other hand, it can learn arbitrary low- and high-order feature interactions implicitly. We conduct comprehensive experiments on three real-world datasets. Our results demonstrate that xDeepFM outperforms state-of-the-art models. We have released the source code of xDeepFM at https://github.com/Leavingseason/xDeepFM.

Single Pt Atoms Confined into a Metal-Organic Framework for Efficient Photocatalysis.

Abstract: It is highly desirable yet remains challenging to improve the dispersion and usage of noble metal cocatalysts, beneficial to charge transfer in photocatalysis. Herein, for the first time, single Pt atoms are successfully confined into a metal-organic framework (MOF), in which electrons transfer from the MOF photosensitizer to the Pt acceptor for hydrogen production by water splitting under visible-light irradiation. Remarkably, the single Pt atoms exhibit a superb activity, giving a turnover frequency of 35 h-1 , ≈30 times that of Pt nanoparticles stabilized by the same MOF. Ultrafast transient absorption spectroscopy further unveils that the single Pt atoms confined into the MOF provide highly efficient electron transfer channels and density functional theory calculations indicate that the introduction of single Pt atoms into the MOF improves the hydrogen binding energy, thus greatly boosting the photocatalytic H2 production activity.

Oxygen Vacancies in ZnO Nanosheets Enhance CO 2 Electrochemical Reduction to CO

Abstract: As electron transfer to CO2 is generally considered to be the critical step during the activation of CO2 , it is important to develop approaches to engineer the electronic properties of catalysts to improve their performance in CO2 electrochemical reduction. Herein, we developed an efficient strategy to facilitate CO2 activation by introducing oxygen vacancies into electrocatalysts with electronic-rich surface. ZnO nanosheets rich in oxygen vacancies exhibited a current density of -16.1 mA cm-2 with a Faradaic efficiency of 83 % for CO production. Based on density functional theory (DFT) calculations, the introduction of oxygen vacancies increased the charge density of ZnO around the valence band maximum, resulting in the enhanced activation of CO2 . Mechanistic studies further revealed that the enhancement of CO production by introducing oxygen vacancies into ZnO nanosheets originated from the increased binding strength of CO2 and the eased CO2 activation.

Ni–Mo–O nanorod-derived composite catalysts for efficient alkaline water-to-hydrogen conversion via urea electrolysis

Abstract: Photo/electrochemical splitting of water to hydrogen (H2) fuel is a sustainable way of meeting our energy demands at no environmental cost, but significant challenges remain: for example, the sluggish anodic reaction imposes a considerable overpotential requirement. By contrast, urea electrolysis offers the prospect of energy-saving H2 production together with urea-rich wastewater purification, whereas the lack of inexpensive and efficient urea oxidation reaction (UOR) catalysts places constraints on the development of this technique. Here we report a porous rod-like NiMoO4 with high oxidation states of the metal elements enabling highly efficient UOR electrocatalysis, which can be readily produced through annealing solid NiMoO4·xH2O as a starting precursor in Ar. This precursor gives the derived Ni/NiO/MoOx nanocomposite when switching the shielding gas from Ar to H2/Ar, exhibiting platinum-like activity for the hydrogen evolution reaction (HER) in alkaline electrolytes. Assembling an electrolytic cell using our developed UOR and HER catalysts as the anode and cathode can provide a current density of 10 milliamperes per square centimeter at a cell voltage of mere 1.38 volts, as well as remarkable operational stability, representing the best yet reported noble-metal-free urea electrolyser. Our results demonstrate the potential of nickel–molybdenum-based materials as efficient electrode catalysts for urea electrolysers that promises cost-effective and energy-saving H2 production.

Nanoparticle-templated nanofiltration membranes for ultrahigh performance desalination

Abstract: Nanofiltration (NF) membranes with ultrahigh permeance and high rejection are highly beneficial for efficient desalination and wastewater treatment. Improving water permeance while maintaining the high rejection of state-of-the-art thin film composite (TFC) NF membranes remains a great challenge. Herein, we report the fabrication of a TFC NF membrane with a crumpled polyamide (PA) layer via interfacial polymerization on a single-walled carbon nanotubes/polyether sulfone composite support loaded with nanoparticles as a sacrificial templating material, using metal-organic framework nanoparticles (ZIF-8) as an example. The nanoparticles, which can be removed by water dissolution after interfacial polymerization, facilitate the formation of a rough PA active layer with crumpled nanostructure. The NF membrane obtained thereby exhibits high permeance up to 53.5 l m−2h−1 bar−1 with a rejection above 95% for Na2SO4, yielding an overall desalination performance superior to state-of-the-art NF membranes reported so far. Our work provides a simple avenue to fabricate advanced PA NF membranes with outstanding performance. Nanofiltration membranes are important for water desalination technologies, but designing membranes that achieve both high permeance and high salt rejection remains challenging. Here, the authors use sacrificial nanoparticles in the membrane fabrication process, leading to crumpled structures with ultrahigh permeance.

Fe Isolated Single Atoms on S, N Codoped Carbon by Copolymer Pyrolysis Strategy for Highly Efficient Oxygen Reduction Reaction

Abstract: Heteroatom-doped Fe-NC catalyst has emerged as one of the most promising candidates to replace noble metal-based catalysts for highly efficient oxygen reduction reaction (ORR). However, delicate controls over their structure parameters to optimize the catalytic efficiency and molecular-level understandings of the catalytic mechanism are still challenging. Herein, a novel pyrrole-thiophene copolymer pyrolysis strategy to synthesize Fe-isolated single atoms on sulfur and nitrogen-codoped carbon (Fe-ISA/SNC) with controllable S, N doping is rationally designed. The catalytic efficiency of Fe-ISA/SNC shows a volcano-type curve with the increase of sulfur doping. The optimized Fe-ISA/SNC exhibits a half-wave potential of 0.896 V (vs reversible hydrogen electrode (RHE)), which is more positive than those of Fe-isolated single atoms on nitrogen codoped carbon (Fe-ISA/NC, 0.839 V), commercial Pt/C (0.841 V), and most reported nonprecious metal catalysts. Fe-ISA/SNC is methanol tolerable and shows negligible activity decay in alkaline condition during 15 000 voltage cycles. X-ray absorption fine structure analysis and density functional theory calculations reveal that the incorporated sulfur engineers the charges on N atoms surrounding the Fe reactive center. The enriched charge facilitates the rate-limiting reductive release of OH* and therefore improved the overall ORR efficiency.

Neural Architecture Optimization

Abstract: Automatic neural architecture design has shown its potential in discovering powerful neural network architectures. Existing methods, no matter based on reinforcement learning or evolutionary algorithms (EA), conduct architecture search in a discrete space, which is highly inefficient. In this paper, we propose a simple and efficient method to automatic neural architecture design based on continuous optimization. We call this new approach neural architecture optimization (NAO). There are three key components in our proposed approach: (1) An encoder embeds/maps neural network architectures into a continuous space. (2) A predictor takes the continuous representation of a network as input and predicts its accuracy. (3) A decoder maps a continuous representation of a network back to its architecture. The performance predictor and the encoder enable us to perform gradient based optimization in the continuous space to find the embedding of a new architecture with potentially better accuracy. Such a better embedding is then decoded to a network by the decoder. Experiments show that the architecture discovered by our method is very competitive for image classification task on CIFAR-10 and language modeling task on PTB, outperforming or on par with the best results of previous architecture search methods with a significantly reduction of computational resources. Specifically we obtain $2.11\%$ test set error rate for CIFAR-10 image classification task and $56.0$ test set perplexity of PTB language modeling task. The best discovered architectures on both tasks are successfully transferred to other tasks such as CIFAR-100 and WikiText-2. Furthermore, combined with the recent proposed weight sharing mechanism, we discover powerful architecture on CIFAR-10 (with error rate $3.53\%$) and on PTB (with test set perplexity $56.6$), with very limited computational resources (less than $10$ GPU hours) for both tasks.

Hybrid 2D Dual-Metal–Organic Frameworks for Enhanced Water Oxidation Catalysis

Abstract: Metal-organic frameworks (MOFs) and MOF-derived nanostructures have recently been emerging as promising catalysts for electrocatalysis applications. Herein, twodimensional (2D) MOFs nanosheets decorated with Fe-MOF nanoparticles are synthesized and evaluated as the catalysts for water oxidation catalysis in alkaline medium. A dramatic enhancement of the catalytic activity is demonstrated by introduction of electrochemically inert Fe-MOF nanoparticles onto active 2D MOFs nanosheets. In the case of active Ni-MOF nanosheets (Ni-MOF@Fe-MOF), the overpotential is 265 mV to reach a current density of 10 mA cm in 1 M KOH, which is lowered by ca. 100 mV after hybridization due to the 2D nanosheet morphology and the synergistic effect between Ni active centers and Fe species. Similar performance improvement is also successfully demonstrated in active NiCo-MOF nanosheets. More importantly, the real catalytic active species in the hybrid Ni-MOF@FeMOF catalyst are unraveled. We find that, NiO nanograins (~5 nm) are formed in situ during OER process and act as OER active centers as well as building blocks of the porous nanosheet catalysts. These findings provide new insights into understanding MOF-based catalysts for

Synergetic interaction between neighbouring platinum monomers in CO 2 hydrogenation.

Abstract: Exploring the interaction between two neighbouring monomers has great potential to significantly raise the performance and deepen the mechanistic understanding of heterogeneous catalysis. Herein, we demonstrate that the synergetic interaction between neighbouring Pt monomers on MoS2 greatly enhanced the CO2 hydrogenation catalytic activity and reduced the activation energy relative to isolated monomers. Neighbouring Pt monomers were achieved by increasing the Pt mass loading up to 7.5% while maintaining the atomic dispersion of Pt. Mechanistic studies reveal that neighbouring Pt monomers not only worked in synergy to vary the reaction barrier, but also underwent distinct reaction paths compared with isolated monomers. Isolated Pt monomers favour the conversion of CO2 into methanol without the formation of formic acid, whereas CO2 is hydrogenated stepwise into formic acid and methanol for neighbouring Pt monomers. The discovery of the synergetic interaction between neighbouring monomers may create a new path for manipulating catalytic properties.

Few-layer graphdiyne doped with sp-hybridized nitrogen atoms at acetylenic sites for oxygen reduction electrocatalysis.

Abstract: The oxygen reduction reaction (ORR) is a fundamental reaction for energy storage and conversion. It has mainly relied on platinum-based electrocatalysts, but the chemical doping of carbon-based materials has proven to be a promising strategy for preparing metal-free alternatives. Nitrogen doping in particular provides a diverse range of nitrogen forms. Here, we introduce a new form of nitrogen doping moieties —sp-hybridized nitrogen (sp-N) atoms into chemically defined sites of ultrathin graphdiyne, through pericyclic replacement of the acetylene groups. The as-prepared sp-N-doped graphdiyne catalyst exhibits overall good ORR performance, in particular with regards to peak potential, half-wave potential and current density. Under alkaline conditions it was comparable to commercial Pt/C, and showed more rapid kinetics. And although its performances are a bit lower than those of Pt/C in acidic media they surpass those of other metal-free materials. Taken together, experimental data and density functional theory calculations suggest that the high catalytic activity originates from the sp-N dopant, which facilitates O2 adsorption and electron transfer on the surface of the catalyst. This incorporation of chemically defined sp-N atoms provides a new synthetic route to high-performance carbon-based and other metal-free catalysts.