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Researchers Propose a High-loaded Electrocatalyst with High-efficient Performance Expression in PEMFCs

An interdisciplinary research team led by Prof. YANG Hui and Prof. JIANG Zheng of Shanghai Advanced Research Institute reported a high-loaded (44.7 wt.%) and sub-6 nm Pt IMC catalyst, which can be controllable synthesized through a cobalt oxide aided structural-evolution strategy.

　　Highly-active and durable low-Pt electrocatalysts that can dramatically reduce the costly Pt usage in the oxygen reduction reaction (ORR) are urgently required for the commercialization of fuel cell vehicles. Cost-effective Pt-based intermetallic (IMC) catalysts have been regarded as the most promising alternative to boost activity and durability towards ORR, however, the formation of high-loaded Pt-based IMCs usually involves the high-temperature annealing that leads to severe agglomeration and nonuniformity of IMC nanoparticles (NPs), imposing an enormous challenge on efficient synthesis.
　　Motivated by such a challenge, an interdisciplinary research team led by Prof. YANG Hui and Prof. JIANG Zheng of Shanghai Advanced Research Institute reported a high-loaded (44.7 wt.%) and sub-6 nm Pt IMC catalyst, which can be controllable synthesized through a cobalt oxide aided structural-evolution strategy. The results were published in Energy & Environmental Science recently.
　　The as-prepared catalyst exhibited superb electrocatalytic performance for the ORR with a greatly enhanced mass activity (MA@0.9 V) of 0.53 A mg(Pt)-1 and durability in model electrode measurements.
　　Impressively, the resultant catalyst delivered a record-high power density (2.30/1.23 Wcm-2 for H2-O2/air) and extraordinary stability. Particularly, the MA@0.9 V calculated from fuel cell reaches 0.46 Amg(Pt)-1 in MEA configuration, exceeding the 2020 DOE target (0.44 Amg(Pt)-1 ) and very close to the intrinsic value, indicating that excellent activity can be highly efficient expression under PEMFC operating conditions.
　　The synthetic approach developed in this report provides a feasible strategy for the development of high-loaded, small-sized fuel cell electrocatalysts with high activity expression, paving a new way for future practical application of low-Pt catalysts in fuel cells.
　　Structural feature and electrocatalytic performance of the prepared PtCo-IMC catalysts (Image by Prof. YANG’s group)
　　

2021-12-10 more+

Scientists Propose Novel Bilayer Structure for Crystalline Silicon Solar Cells

　　Researchers from the Shanghai Advanced Research Institute of the Chinese Academy of Sciences have proposed a novel “bilayer” structure composing of different transition metal oxide (TMO) thin films in crystalline silicon (c-Si) solar cells in order to improve the cells’ efficiency.
　　The researchers combined NiOx and MoOx films into a bilayer structure that extracts “hole carriers” from c-Si more efficiently than single-layer films can. The results were published in Cell Reports Physical Science.
　　“Hole carriers” carry a positive charge. Together with electrons, which have opposite polarity, they were created after c-Si absorbs sun light. By extracting positive holes and negative electrons from c-Si to external circuits, the sun light is converted to usable electricity – this is what a c-Si solar cell does. “Extracting” carriers from c-Si is critical and they can be realized by carrier-selective contacts (CSCs) such as TMO films.
　　CSCs play an important role in improving the power conversion efficiency (PCE) of c-Si cells. Existing single-layer, thin TMO films such as MoOx or NiOx cannot effectively extract the desired carriers—mainly holes—thus leading to c-Si solar cells with mediocre efficiency.
　　In a NiOx/MoOx bilayer structure, however, MoOx can induce band bending at the interface, which is favorable for hole carrier extraction. Moreover, NiOx helps to block undesired electron carriers. This is confirmed by both band alignment simulation and minority carrier lifetime measurements.
　　Taking advantages of these features, the researchers reported a remarkable PCE of 21.31% in c-Si solar cells employing NiOx/MoOx bilayers.
　　Moreover, forming an additional ultra-thin SiOx layer on the silicon surface can further suppress loss pathways such as recombination, etc.
　　As a consequence, using an NiOx/SiOx/MoOx structure can further boost the device’s PCE to 21.60%. This is the highest reported efficiency of any c-Si solar cell employing MoOx-based hole-selective contacts instead of a costly a-Si:H passivation layer,according to the researchers.
　　This study highlights a promising and robust approach to employing bilayers as efficient structures for extracting hole carriers. It serves as an inspiring guide for tackling challenges in the field of passivating contact c-Si solar cells.
　　The first author of the publication is LI Le (PhD candidate), the corresponding authors are Dr. ZHANG Shan-Ting and Prof. LI Dongdong. This work was supported by the National Natural Science Foundation of China, the Natural Science Foundation of Shanghai, and the Shanxi Science and Technology Department, among others.
　　
　　Photovoltaic performance of the c-Si solar cells employing NiOx/MoOx bilayer as hole-selective contacts. (Image by SARI)
　　

2021-12-08 more+

Scientists Achieved Direct Conversion of CO2 to a Jet Fuel over CoFe Alloy Catalysts

Direct conversion of carbon dioxide (CO2) using green hydrogen is a sustainable approach to jet fuel production. However, achieving a high level of performance remains a challenge due to the inertness of CO2 and its low activity for subsequent C–C bond formation. a research team led by Prof. Gao Peng, Prof. Li Shenggang and Prof. Sun Yuhan at Shanghai Advanced Research Institute (SARI) reported a Na-modified CoFe alloy catalyst using layered double-hydroxide precursors that directly transforms CO2 to a jet fuel composed of C8-C16 jet-fuel-range hydrocarbons with very high selectivity.

　　The increased consumption of fossil resources is responsible for the emission of large amounts of anthropogenic CO2, which results in climate change and ocean acidification. Direct conversion of carbon dioxide (CO2) using green hydrogen is a sustainable approach to jet fuel production. However, achieving a high level of performance remains a challenge due to the inertness of CO2 and its low activity for subsequent C–C bond formation.
　　Motivated by such a formidable challenge, a research team led by Prof. Gao Peng, Prof. Li Shenggang and Prof. Sun Yuhan at Shanghai Advanced Research Institute (SARI) of the Chinese Academy of Sciences reported a Na-modified CoFe alloy catalyst using layered double-hydroxide precursors that directly transforms CO2 to a jet fuel composed of C8-C16 jet-fuel-range hydrocarbons with very high selectivity. The research results were published in The Innovation entitled "Direct conversion of CO2 to a jet fuel over CoFe alloy catalysts”.
　　The Na-modified CoFe alloy catalyst demonstrates a highly efficient production of jet-fuel-range hydrocarbons with an unprecedentedly high C8-C16 selectivity of 63.5% with 10.2% CO2 conversion as well as a low combined selectivity of less than 22% toward undesired CO and CH4 via direct CO2 hydrogenation (Figure 1).
　　Figure 1. The evaluation data of CO2 hydrogenation over CoFe-0.81Na catalyst. Effects of (A) space velocity and (B) reaction temperature on conversion of CO2, selectivity of CO, and hydrocarbon distribution (Image by SARI)
　　Structural characterization reveals that the Co7Fe3 alloy structure inhibits CH4 formation and plays a crucial role in the selectivity hydrogenation of CO2 to the higher hydrocarbons that constitute jet fuel.
　　The spectroscopic studies suggest that the CoFe alloy surface has a remarkable inhibitory effect on CH4 production via CO2 methantion and the metallic CoFe alloy is the active phase responsible for producing C2+ hydrocarbons from the CO intermediate, whose formation is facilitated by the iron oxide surface sites generated in situ during the CO2 hydrogenation reaction.
　　Density functional theory calculations show that the CoFe catalyst surface has a lower tendency for the C-C coupling reactions than the Co catalyst surface, as reflected from both the calculated energy barriers and reaction energies (Figure 2). This contributes to the narrower carbon distribution from hydrogenation of the CO intermediate over the CoFe catalyst, compared to the Co catalyst.
　　The calculations further show that formation of the CoFe alloy suppresses the CO2 methanation reaction by increasing the energy barrier for the dissociation of the CH3O* intermediate, leading to a lower methane selectivity than that over the Co catalyst. These theoretical predictions are in good agreement with our experimental observations.
　　Figure 2. Density functional theory studies on CO2 hydrogenation to jet fuel. Potential energy profiles of the C-C coupling and CH* hydrogenation over (A) Co and (B) CoFe catalyst surfaces, and (C) of the CH3O* dissociation on Co, CoFe and CoO surfaces. Transition state structures of (D) C-C coupling, (E) CH* hydrogenation, and (F) CH3O* dissociation over the CoFe catalyst surface, and (G) charge density difference of the CH3O* adsorbate over the CoFe catalyst surface. (Image by SARI)
　　This study provides a viable technique for the highly selective synthesis of eco-friendly and carbon-neutral jet fuel from CO2, which can potentially facilitate the rational development of efficient materials for the direct hydrogenation of CO2 to advanced liquid fuels.

2021-11-11 more+

Scientists Reveal the Uniqueness of Ullmann Reaction Path

a research team reported that the Ullmann reaction path is unique regardless of predesigned assembled structures, dominated by the fact that weak intermolecular interaction in assembled nanostructures is suppressed by strong covalent bonding during reactions.

　　On-surface Ullmann coupling has been intensely utilized for the tailor-made fabrication of conjugated frameworks towards molecular electronics, however, reaction mechanisms are still limitedly understood. While manipulating the noncovalent intramolecular interaction and cage effect on surface have been proven to be effective in steering Ullmann coupling reactions, reaction mechanisms are still under intensive investigation nowadays.
　　Motivated by such a challenge, a research team led by Prof. Fei Song at Shanghai Advanced Research Institute (SARI), along with collaborators from Shanghai Institute of Applied Physics, Soochow University, Central South University and Harbin Institute of Technology, reported that the Ullmann reaction path is unique regardless of predesigned assembled structures, dominated by the fact that weak intermolecular interaction in assembled nanostructures is suppressed by strong covalent bonding during reactions. The research results were published in Nano Research entitled "Identifying the convergent reaction path from predesigned assembled structures: Dissymmetrical dehalogenation of Br2Py on Ag(111)”.
　　Surface Ullmann coupling of 2,7-dibromopyrene (Br2Py) on Ag (111) has been elucidated by scanning tunnelling microscopy (STM), X-ray photoelectron, spectroscopy (XPS) and density function theory (DFT). By manipulating deposition conditions, diverse assembled architectures have been constructed for Br2Py on Ag (111). Stepwise annealing leads to an identical reaction diagram for the surface Ullmann coupling from individual assembled structures convergent into the brick-wall-pattern OM dimers first, and then into elongated OM chains in order and eventually long-range polymers with direct C–C coupling. While the reaction mechanism is demonstrated to be dominated by the metal coordinated and halogen bonding motifs, interestingly, it has also been revealed that surface adatoms and dissociated Br atoms play a crucial role in coupling reactions.
　　Although previous reports have claimed that pre-self-assembly strategy can be utilized to steer Ullmann reaction paths and intermediate species, however, for Br2Py on Ag (111) herein, distinct phenomenon is observed while no apparent relationship is found between predesigned nanostructures and reaction path (reactants). Thus, this report proposes essential insights on fundamental understanding of surface Ullmann coupling towards high-yield surface synthesis of functional nanostructures for nono-electronics.
　　Convergent reaction path from diverse assembled structures. (Image by Prof. SONG’s group)

2021-05-25 more+

Researchers Develop a Novel Approach to Heterogeneous Photosynthesis of Azo- Compounds in Continuous Flow

a research team reported a novel approach of gas-liquid-solid segmented flow, which enabled utilizing the solid photocatalysis in continuous flow without clogging. Owning to the inner recirculation in liquid segments and the formed thin film, this method ensures the effective suspension of solid catalysts in flow, resulting in enhanced mass transfer and irradiation.

　　Photocatalytic reactions, which allow unlocking some chemical transformations under mild conditions that are unavailable to conventional ground-state pathways, can save energy consumption and improve intrinsic safety of the processes. As a sustainable and low-carbon technology, it has high potential to contribute to the national commitment of carbon peak and carbon neutrality. Continuous flow chemistry can, to a large extent, migrate the “light limitation” problem in traditional batch protocols, and the use of heterogeneous photocatalysis can overcome the disadvantages of difficult catalyst recovery in homogeneous systems. However, effective handling of the solid photocatalysis in continuous flow still remains very challenging.
　　Motivated by such a challenge, a research team led by Prof. TANG Zhiyong and Associate Prof. Zhang Jie at Shanghai Advanced Research Institute (SARI), Chinese Academy of Sciences, reported a novel approach of gas-liquid-solid segmented flow, which enabled utilizing the solid photocatalysis in continuous flow without clogging. Owning to the inner recirculation in liquid segments and the formed thin film, this method ensures the effective suspension of solid catalysts in flow, resulting in enhanced mass transfer and irradiation. The research results were published in Chemical Engineering Journal entitled “Tuning the Gas-Liquid-Solid Segmented Flow for Enhanced Heterogeneous Photosynthesis of Azo- Compounds” .
　　Azobenzene and azoxybenzene are important precursors in pigment industry, electronic industry and pharmaceutical industry. In this work, the selective synthesis of azo- compounds from nitrobenzene by graphitic carbon nitride (g-C3N4) photocatalysis was selected as model photocatalytic reaction. By combing the visual flow experiments, the model reaction under gas-liquid-solid segmented flow was investigated thoroughly. Meanwhile, the effects of flow behavior on the photoreaction performance were quantified.
　　Scientists found that the continuous flow could greatly shorten the reaction time. The photocatalytic reaction performance was very sensitive to the gas-liquid-solid segmented flow conditions, which needed to be carefully tuned. It was identified that the increasing inert gas fraction resulted in more stable segmented flow with shorter liquid segments and thinker liquid film. The maximum productivity per volume of the continuous photo-microreactor reached 26.1 mmol/h*L. Benefiting from the advantage of “numbering-up”, this value was more than 500 times that of the batch reactor (80 L) reported in the open literature. These results demonstrated great potential of gas-liquid-solid segmented flow in the field of heterogeneous photocatalysis.
　　This work provides a new route to utilize the heterogenous catalysis in continuous flow, which can be applied as a universal method to intensify the synthesis of functional materials, fine chemicals and active pharmaceutical ingredients (APIs), thereby promoting the transformation from conventional batch processes to green, safe and efficient continuous flow processes.
　　This work was supported by the Youth Innovation Promotion Association of Chinese Academy of Sciences, the STS Program of Chinese Academy of Sciences, and Frontier Scientific Research Project funded by Shell.
　　Figure 1. Heterogeneous photosynthesis of azo- compounds in gas-liquid-solid segmented flow (Image by SARI)
　　Figure 2. Comparison of the photocatalytic performance between (a) the batch reactor and (b) the continuous flow microreactor (Image by SARI)
　　Figure 3. Effects of total flow rate on the nitrobenzene conversion and the liquid segment length in the gas-liquid-solid segmented flow (Image by SARI)
　　Contact: TANG Zhiyong
　　Shanghai Advanced Research Institute, Chinese Academy of Sciences
　　Email: tangzy@sari.ac.cn
　　

2021-05-17 more+

Researchers Propose a Novel Approach to Precisely Control the Gas-liquid Taylor Flow Pattern for Continuous Flow Chemistry

A research team reported a novel approach of adding pulsation field to precisely regulate the gas-liquid Taylor Flow.

　　Microreactor exhibits great potential for intensified synthesis of advanced materials and chemicals in continuous flow mode, for its various advantages such as excellent heat and mass transfer efficiency, high controllability, easy scale-up, etc. Among numerous flow patterns, gas-liquid Taylor flow represents the characteristics of wide operation window, low axial back mixing and good radial mixing, thus, has been proven as an ideal flow regime to enhance chemical reactions. However, the method to precisely control the Taylor flow pattern is still lacking.
　　Motivated by such a challenge, a research team led by Prof. TANG Zhiyong and Associate Prof. Zhang Jie at Shanghai Advanced Research Institute (SARI), Chinese Academy of Sciences, reported a novel approach of adding pulsation field to precisely regulate the gas-liquid Taylor Flow. The research results were published in Chemical Engineering Journal entitled “Regulation of Gas-Liquid Taylor Flow by Pulsating Gas Intake in Micro-channel” .
　　In this work, the research team used a simple valve arrangement to introduce the pulsation filed, thus producing periodic acceleration and deceleration motion of liquid slugs. By combing visual flow experiments with computational fluid dynamics (CFD) simulation, the temporal-spatial migration of the Taylor flow pattern under pulsating gas intake conditions was investigated. A high-speed camera is used to track the trajectory of gas-liquid interface by the Lagrangian method, while the numerical simulation is used to acquire the flow field distribution at different moments using the Euler method. Meanwhile, the involved forces during bubble formation and the characteristics of bubble length and velocity under pulsation were analyzed in detail.
　　By studying the temporal-spatial migration of the pattern, scientists found that the pulsation can increase the power of inertial force on the Taylor flow pattern. Moreover, the pattern can be destroyed when the pulsation energy exceeds a certain value.
　　This work provides a new route to regulate precisely the gas-liquid Taylor flow, and will contribute to future applications of this technique to intensify various gas-liquid reactions in continuous flow.
　　This work was supported by the Youth Innovation Promotion Association of Chinese Academy of Sciences, the STS Program of Chinese Academy of Sciences and Frontier Scientific Research Project funded by Shell.
　　Figure 1. Regulation of Gas-Liquid Taylor Flow by Pulsating Gas Intake in Micro-channel (Image by SARI)
　　Figure 2 Space-time distribution of gas fraction in bubble formation process (Image by SARI)
　　Figure 3 (a) Forces versus pulse frequency f at the T-junction, (b) Bubble velocities at downstream(Image by SARI)
　　

2021-04-09 more+

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