Researchers Reveal a Dynamic Mechanism for Ni–Au Bimetallic Nanoparticles during CO2 Hydrogenation

The high catalytic performance of core–shell nanoparticles (NP) is usually attributed to the syngergy of distinct geometric and electronic structures. Although the general assumption is that core–shell NPs maintain their configuration under working conditions, it remains unclear whether they maintain their structure throughout a reaction.Scientists recently reported a different working mechanism and demonstrated that the core–shell structure may not exist under a specific set of conditions, which overturns the conventional understanding.

　　The high catalytic performance of core–shell nanoparticles (NP) is usually attributed to the syngergy of distinct geometric and electronic structures. Although the general assumption is that core–shell NPs maintain their configuration under working conditions, it remains unclear whether they maintain their structure throughout a reaction.
　　Scientists recently reported a different working mechanism and demonstrated that the core–shell structure may not exist under a specific set of conditions, which overturns the conventional understanding.
　　 
　　The results appear in a study conducted by a team from the Shanghai Advanced Research Institute (SARI) of the Chinese Academy of Sciences (CAS) along with other collaborators in the latest issue of Nature Catalysis entitled “Reversible loss of core–shell structure for Ni–Au bimetallic nanoparticles during CO2 hydrogenation.”
　　 
　　The scientists use environmental transmission electron microscopy (ETEM) to directly visualize the dynamic process at atomic level, coupled with multiple state-of-the-art in situ techniques, including synchrotron X-ray absorption spectroscopy, infrared spectroscopy and theoretical simulations, to precisely analyze the imaging conditions of over 3,000 high-resolution transmission electron microscopy (TEM) images.
　　 
　　By tracing the real-time changes of the surface atomic structure during the entire reaction process, the result exhibits a highly selective CO production in CO2 hydrogenation, features an intact ultrathin Au shell over the Ni core before and after the reaction. However, the catalytic performance could not be attributed to the Au shell surface, but rather to the formation of a transient reconstructed alloy surface, promoted by CO adsorption during the reaction.
　　 
　　Density functional theory (DFT) calculations also confirmed that it is the kinetically alloyed surface, rather than the ultrathin Au shell surface, that is catalytically active during the highly selective reverse water gas shift reaction.
　　 
　　The discovery of such a reversible transformation urges us to reconsider the reaction mechanism beyond the stationary model, and may have important implications not only for core–shell nanoparticles, but also for other well-defined nanocatalysts.
　　Dynamic Mechanism for Ni–Au Bimetallic Nanoparticles during CO2 Hydrogenation (Image by SARI)
　　In situ observation and theoretical interpretation of the structural transition of NiAu NPs during the reaction (Figures adapted from Nature Catalysis)
　　Contact: GAO Yi
　　Shanghai Advanced Research Institute, Chinese Academy of Sciences
　　Email: gaoyi@zjlab.org.cn
　　

Novel Approach to Pt Electroless Deposition for Highly Efficient Hydrogen Evolution

The small size and large specific surface area intrinsically associated with Pt atomic clusters pose challenges in the synthesis and stabilization of Pt-ACs without agglomeration. A research team reported a novel one-step carbon-defect-driven electroless deposition (ELD) method to produce ultrasmall but well-defined and stable Pt-ACs supported by defective graphene (Pt-AC/DG) structures.

　　Pt atomic clusters (Pt-ACs) display outstanding electrocatalytic performance because of their unique electronic structure with a large number of highly exposed surface atoms. However, the small size and large specific surface area intrinsically associated with ACs pose challenges in the synthesis and stabilization of Pt-ACs without agglomeration.
　　 
　　Motivated by such a challenge, a research team led by Prof. YANG Hui at Shanghai Advanced Research Institute (SARI) of the Chinese Academy of Sciences collaborated with Prof. DAI Liming at Case Western Reserve University of the United States reported a novel one-step carbon-defect-driven electroless deposition (ELD) method to produce ultrasmall but well-defined and stable Pt-ACs supported by defective graphene (Pt-AC/DG) structures. The research results were published in the Journal of the American Chemical Society entitled " Carbon-Defect-Driven Electroless Deposition of Pt Atomic Clusters for Highly Efficient Hydrogen Evolution”.
　　 
　　A theoretical simulation clearly revealed that the defective regions with a lower work function, and hence a higher reducing capacity, than that of normal hexagonal sites triggered the reduction of Pt ions preferentially at the defect sites.
　　 
　　Moreover, the strong binding energy between Pt and carbon defects effectively restricted the migration of spontaneously reduced Pt atoms to immobilize/stabilize the resultant Pt-ACs.
　　 
　　The prepared Pt-AC/DG catalysts exhibited superb electrocatalytic performance for the hydrogen evolution reaction (HER) with a greatly enhanced Pt utilization efficiency and stability with significantly reduced Pt usage compared with the use of commercial Pt/C catalysts.
　　 
　　Water electrolysis based on renewable energy is the key of hydrogen production. However, large usage of precious metal catalysts is the primary reason of high costs in HER. The study provides an ideal strategy for the future development of cost effective Pt-based catalysts for the HER and many other reactions.
　　Electrocatalytic performance of the prepared Pt-AC/DG catalysts (Image by Prof. YANG’s group)
　　Contact: YANG Hui
　　Shanghai Advanced Research Institute, Chinese Academy of Sciences
　　Email: yangh@sari.ac.cn
　　

Researchers Develop an Intelligent Spectrum Sensing Technique for 5G communications

The ongoing 5G communication involves diversified scenarios with different characteristics and diverse requirements, which makes spectrum sensing methods difficult to serve various applications flexibly while maintaining satisfactory performance. Motivated by such a challenge,researchers provided a novel spectrum sensing technique, seeking a feasible way to combine the reinforcement learning concept with advanced spectrum sensing methods so as to optimize the performance of the cognitive radio network under multifarious scenarios in 5G communications.

　　Spectrum sensing plays an important role in future wireless communication systems as it helps to resolve the coexistence issue and optimize spectrum efficiency. However, the ongoing 5G communication involves diversified scenarios with different characteristics and diverse requirements, which makes spectrum sensing methods difficult to serve various applications flexibly while maintaining satisfactory performance. The scarcity of spectrum resource remains a critical challenge for 5G communications.
　　 
　　Motivated by such a challenge, a research team led by Prof. HU Honglin and Prof. XU Tianheng at Shanghai Advanced Research Institute (SARI) of the Chinese Academy of Sciences provided a novel spectrum sensing technique, seeking a feasible way to combine the reinforcement learning concept with advanced spectrum sensing methods so as to optimize the performance of the cognitive radio network under multifarious scenarios in 5G communications. The research results were published in the latest issue of IEEE Wireless Communications entitled “Intelligent Spectrum Sensing: When Reinforcement Learning Meets Automatic Repeat Sensing in 5G Communications.”
　　 
　　The research team analyzes different requirements of several typical 5G scenarios, and categorizes three dedicated models with respective optimization targets for spectrum sensing techniques. In order to be adaptive for various optimization targets, scientists have designed the architecture for the intelligent spectrum sensing technique, trying to take account of both instability and adaptability issues. Numerical results manifested that the proposed sensing technique has the capability of adapting to various scenarios with different optimization targets.  
　　 
　　The research results are promising for practical applications. They have been applied in the SEANET system developed by CAS and Alpha, a campus network constructed by CAS and ShanghaiTech University. The results also contribute to further deployment and promotion of 5G and next generation communication system in China.
　　 
　　This research was supported in part by the National Natural Science Foundation of China, the Shanghai Rising-Star Program, the Shanghai Young Talent Sailing Program and the Program of Shanghai Academic Research Leader.
　　Three typical spectrum sensing involved scenarios in 5G communications: that is, throughput-oriented scenarios (a), energy saving-oriented scenarios (b), and sensing accuracy-oriented scenarios(c) (Image by SARI)
　　Reinforcement-learning-driven automatic repeat sensing mechanism (Image by SARI)
　　Performance comparison among three intelligent sensing strategies: a) Sensing accuracy performance; b) Throughput performance (Image by SARI)
　　Contact: HU Honglin
　　Shanghai Advanced Research Institute, Chinese Academy of Sciences
　　Email:huhl@sari.ac.cn

Shanghai scientists make breakthrough in X-ray research

　　In 2021, breakthroughs have been made continuously for debugging of Shanghai soft X-ray free electron laser, and has pushed the shortest wavelength of free electron laser of China to 2nm, and firstly realized full band coverage of the "water window" among the 3 soft X-ray free electron laser facilities around the world.
　　The "water window" refers to a soft X-ray with a wavelength that has a range between 2.3 and 4.4 nanometers. Water is relatively transparent to X-rays but other essential life elements, such as carbon, still interact strongly with X-rays. As such, the "water window" soft X-rays provide a unique opportunity for investigating biological materials, added the researchers.
　　Scientists said that this achievement means that X-ray FEL research in China has advanced from the facility research and development phase to user operation phase. Within the "water window", SXFEL can generate high-intensity free electron laser pulses, which are 1 billion times brighter than those of synchrotron radiation light sources. Such ultrabright, ultrafast and coherent pulses enable scientists to take X-ray snapshots of atoms and molecules at work, revealing fundamental processes in materials, technology and living organisms.
　　Researchers said that the research result this time will be applied in microscopic imaging of living cells, and may provide a revolutionary research tool for multiple disciplines, including physics, biology and chemistry. The SXFEL facility is scheduled to begin user operation next year and will be open to both users at home and abroad. 

Hybrid Energy System Proposed for a Coal-Based Chemical Industry

Recently, a joint research team proposed a hybrid energy system which integrates nuclear/ renewable energy with coal for a coal-based chemical industry. The latest result was published in the famous scientific journal Joule.

　　Recently, a joint research team from CAS Key Laboratory of Low-Carbon Conversion Science & Engineering of Shanghai Advanced Research Institute (SARI) and SARI-ShanghaiTech University Joint Lab has proposed a hybrid energy system that integrates nuclear/ renewable energy with coal for a coal-based chemical industry. The latest result was published in the famous scientific journal Joule under Cell Press journals on March 14th 2018.
　　The coal to chemicals process by gasification is one of the major carbon conversion technologies, especially in coal- rich countries such as China and the United States. The conventional coal utilization pattern, however, causes a large amount of CO2 emission .
　　Nuclear/ renewable energy can supply heat and electricity for low/high temperature water electrolysis, then the hydrogen will be mixed with the syngas from the coal gasification unit to adjust the H/C ratio for downstream chemicals synthesis processes. In this case, the water- gas shift unit can be eliminated and then the system direct CO2 emission can be significantly reduced. Thus, the hybrid energy system is proposed as a way to mitigate the carbon emission as an effective solution to integrate nuclear/ renewable energy with coal for low-carbon fuel and chemicals production.
　　The hybrid energy system is feasible in most coal- intensive countries and will lead to significant carbon emission reduction potential in the coming 5~15 years. Moreover, with the sharp decline of power cost from renewable/ nuclear energy and the carbon tax introduction, the hybrid system shows potential to become economically competitive. It is estimated that in 2030, the reduction capacity of CO2 emission from hybrid systems is equivalent to 90% of the Japanese CO2 emission (1,345 Mt) in 2014 and 33% of the European CO2 emission (3,696 Mt) in 2014.
　　Figure: the proposed hybrid energy system (image by SARI)
　　In the past few years, the CAS Key Laboratory of Low-Carbon Conversion Science & Engineering has made a series of achievements in the low carbon hybrid energy strategy area. Following the related research results published in Science China, Angew Chem Int Ed , Applied Energy, and Energy Conversion and Management, this work, supported by Chinese Academy of Sciences and SARI’s strategic partner Shell, is another achievement of research and education integration between SARI and ShanghaiTech University, which is also a landmark for the construction of Zhangjiang Comprehensive National Science Center.
　　 

Researchers Develop New Electrocatalysts to Convert CO2 into Value-added Chemicals

Conversion of carbon dioxide (CO2) into fuels and chemicals by electroreduction has attracted significant interest, although it suffers from a large overpotential and low selectivity. A Pd-Sn alloy electrocatalyst was developed for the exclusive conversion of CO2 into formic acid in an aqueous solution.

　　Greenhouse gas carbon dioxide (CO2) is widely considered to be responsible for the climate change, and its utilization as an alternative carbon feedstock may be a viable approach for its remedy. Consequently, electrochemical conversion of CO2into value-added chemicals or fuels has attracted significant interest, although it suffers from a large overpotential and low selectivity. 
　　Recently, a joint research team from CAS Key Laboratory of Low-Carbon Conversion Science & Engineering of Shanghai Advanced Research Institute (SARI) and SARI-ShanghaiTech University Joint Lab has found a new electrocatalyst to exclusively convert CO2 to formic acid, a chemical widely used in medical, chemical and agricultural lines all over the world over the supported Pd-Sn alloy, and thereby realizing the utilization of CO2 as an affordable carbon resource. This is attributed to the tuning of surface electronic structures of supported Pd-Sn alloy NPs. The electrocataytic activity and selectivity are highly dependent on the surface configurations, in which formic acid with the faradaic efficiency of 99% at the lowest overpotential of -0.26 V was produced on the PdSn alloy surface with optimal surface Pd, Sn and O configuration.  
　　On the other hand, the research team has developed a class of mesoporous nitrogen-doped carbon (N-Carbon) tailored with highly uniform cylindrical channel structures to dramatically boost C-C bond formation in CO2 electroreduction. The as-prepared metal-free N-carbon catalyst can convert CO2 into ethanol with the faradaic efficiency as high as 77% at the low potential of ？0.56 V (vs. RHE). As the competitive CO2 reduction into carbon monoxide or other products was completely suppressed, an almost 100% selectivity to ethanol was achieved. This work will open up an avenue for developing robust metal-free carbon-based electrocatalysts for converting CO2 into C2 compounds with high selectivity and efficiency. 
　　The latest result was published in the famous scientific journal Angewandte Chemie International Edition (doi: 10.1002/anie.201707098; doi: 10.1002/ange.201706777). 
　　Electrocatalytic conversion of CO2 into ethanol over nitrogen-doped carbon catalysts (Image by SARI) 
　　This work was supported by the Hundred Talents Program of Chinese Academy of Sciences, the Ministry of Science and Technology, the SARI-ShanghaiTech Low-carbon Joint Lab, and the SARI Innovation Fund.