Recent Progresses in Oxygen Reduction Reaction Electrocatalysts for Electrochemical Energy Applications

Abstract Electrochemical energy storage systems such as fuel cells and metal–air batteries can be used as clean power sources for electric vehicles. In these systems, one necessary reaction at the cathode is the catalysis of oxygen reduction reaction (ORR), which is the rate-determining factor affecting overall system performance. Therefore, to increase the rate of ORR for enhanced system performances, efficient electrocatalysts are essential. And although ORR electrocatalysts have been intensively explored and developed, significant breakthroughs have yet been achieved in terms of catalytic activity, stability, cost and associated electrochemical system performance. Based on this, this review will comprehensively present the recent progresses of ORR electrocatalysts, including precious metal catalysts, non-precious metal catalysts, single-atom catalysts and metal-free catalysts. In addition, major technical challenges are analyzed and possible future research directions to overcome these challenges are proposed to facilitate further research and development toward practical application. Graphic Abstrac

Metal-free photo-induced sulfidation of aryl iodide and other chalcogenation

A photo-induced C-S radical cross-coupling of aryl iodides and disulfides under transition-metal and external photosensitizer free conditions for the synthesis of aryl sulfides at room temperature has been presented, which features mild reaction conditions, broad substrate scope, high efficiency, and good functional group compatibility. The developed methodology could be readily applied to forge C-S bond in the field of pharmaceutical and material science

Representing ethnic minority cultures in China: Museums, heritage, and ethnic minority groups

Ethnic minority groups (shaoshu minzu) have continued to be silenced in Chinese museums’ expert-led representation of their cultures. Museums in China, instrumentalised by the governments, exert their authority over cultural representation through exhibitions to present ideologies such as ‘diversity in unity’. The representational politics of some museums lie behind their inequitable power relations with ethnic minority groups in terms of exhibition making and programmes management, inviting intensive criticism. Drawing upon critical museology and critical heritage studies, this thesis calls for the reconsideration of power relations and the marginalised voice within the interdisciplinary field. It explores the impact of ethnic minority cultural heritage discourses and practices on the representational practices of museums and ethnic minority groups and their relations.This thesis sheds light on how official cultural heritage ideologies and policies shape and change museums’ social roles and their museological practices, and how museums interact with ethnic minority groups and form new connections with them beyond exhibitions. Examining two types of museums dedicated to ethnic minority cultures, the Anthropology Museum of Guangxi and the Longsheng Longji Zhuang Ecomuseum in Guangxi Zhuang Autonomous Region of China, it foregrounds ethnic minority communities’ exercise of their active agency in relation to heritage construction and cultural representation. Both museums framed by the authorised heritage discourses act as heritage agencies that are sites of contact and contestation. This study interrogates how ethnic minority groups’ heritage constructions resist, negotiate or appropriate museological practices within official heritage discourses. It argues that museums’ authoritative cultural representations and practices can be shaped and mobilised by ethnic minority groups to serve their self-representation and self-expression.</div

High Temperature Oxidation and Oxyacetylene Ablation Properties of ZrB₂-ZrC-SiC Ultra-High Temperature Composite Ceramic Coatings Deposited on C/C Composites by Laser Cladding

In order to improve the high temperature oxidation and ablation resistance of C/C composites, ZrB2-ZrC-SiC ultra-high temperature composite ceramic coatings were prepared on C/C composites by laser cladding using Zr, B4C, and Si as raw materials. The microstructure of the coating was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Air isothermal oxidation (1600 °C, 80 min) and oxyacetylene flame ablation (2400 kW/m2, 300 s) were used to evaluate the high-temperature oxidation and ablation properties of the coating, respectively. The results show that the microstructure of laser cladding coating is a totem of black and white. The white part is mainly the first solidified high melting point ZrB2 phase, and the black part is the latter solidified eutectic structure, which is mainly composed of ZrB2(ZrB12)-ZrC or ZrB2(ZrB12)-SiC two phases. After oxidation at 1600 °C and 80 min, the coating is mainly composed of ZrO2 and ZrSiO4 phases, and ZrSiO4 is basically distributed among ZrO2 particles. The high temperature oxidation and ablation properties of the coating are better than the C/C composite matrix, and the mass ablation rate of the coating is about 1/4 of the latter

Capsule networks embedded with prior known support information for image reconstruction

Compressed sensing (CS) has been successfully applied to realize image reconstruction. Neural networks have been introduced to the CS of images to exploit the prior known support information, which can improve the reconstruction quality. Capsule Network (Caps Net) is the latest achievement in neural networks, and can well represent the instantiation parameters of a specific type of entity or part of an object. This study aims to propose a Caps Net with a novel dynamic routing to embed the information within the CS framework. The output of the network represents the probability that the index of the nonzero entry exists on the support of the signal of interest. To lead the dynamic routing to the most likely index, a group of prediction vectors is designed determined by the information. Furthermore, the results of experiments on imaging signals are taken for a comparation of the performances among different algorithms. It is concluded that the proposed capsule network (Caps Net) creates higher reconstruction quality at nearly the same time with traditional Caps Net

Logging Pattern Detection by Multispectral Remote Sensing Imagery in North Subtropical Plantation Forests

Forest logging detection is important for sustainable forest management. The traditional optical satellite images with visible and near-infrared bands showed the ability to identify intensive timber logging. However, less intensive logging is still difficult to detect with coarse spatial resolution such as Landsat or high spatial resolution in fewer spectral bands. Although more high-resolution remote sensing images containing richer spectral bands can be easily obtained nowadays, the questions of whether they facilitate the detection of logging patterns and which spectral bands are more effective in detecting logging patterns, especially in selective logging, remain unresolved. Therefore, this paper aims to evaluate the combinations of visible, near-infrared, red-edge, and short-wave infrared bands in detecting three different logging intensity patterns, including unlogged (control check, CK), selective logging (SL), and clear-cutting (CC), in north subtropical plantation forests with the random forest algorithm using Sentinel-2 multispectral imagery. This study aims to explore the recognition performance of different combinations of spectral bands (visual (VIS) and near-infrared bands (NIR), VIS, NIR combined with red-edge, VIS, NIR combined with short-wave infrared bands (SWIR), and full-spectrum bands combined with VIS, NIR, red edge and SWIR) and to determine the best spectral variables to be used for identifying logging patterns, especially in SL. The study was conducted in Taizishan in Hubei province, China. A total of 213 subcompartments of different logging patterns were collected and the random forest algorithm was used to classify logging patterns. The results showed that full-spectrum bands which contain the red-edge and short-wave infrared bands improve the ability of conventional optical satellites to monitor forest logging patterns and can achieve an overall accuracy of 85%, especially for SL which can achieve 79% and 64% for precision and recall accuracy, respectively. The red-edge band (698&ndash;713 nm, B5 in Sentinel-2), short-wave infrared band (2100&ndash;2280 nm, B12 in Sentinel-2), and associated vegetation indices (NBR, NDre2, and NDre1) enhance the sensitivity of the spectral information to logging patterns, especially for the SL pattern, and the precision and recall accuracy can improve by 10% and 6%, respectively. Meanwhile, both clear-cutting and unlogged patterns could be well-classified whether adding a red-edge or SWIR band or both in VIS and NIR bands; the best precision and recall accuracies for clear-cutting were enhanced to 97%, 95% and 81%, 91% for unlogged, respectively. Our results demonstrate that the optical images have the potential ability to detect logging patterns especially for the clear-cutting and unlogged patterns, and the selective logging detection accuracy can be improved by adding red-edge and short-wave infrared spectral bands

Analysis of control interaction between D-PMSGs-based wind farm and SVC

According to an accident analysis report, with regard to sub-synchronous oscillation (SSO) in Xinjiang, China, dynamic reactive compensation devices have great influence on the existence of sub-synchronous harmonics. This paper based on the practical phenomenon for further study, focuses on the interaction between direct-drive permanent synchronous generators (D-PMSGs)-based wind farm and static var compensator (SVC). Detailed electro-magnetic transient simulation model, such as D-PMSGs-based wind farm compensated by SVC, is established in PSCAD/EMTDC. Time-domain simulation results demonstrate that there is interaction between D-PMSGs-based wind farm and SVC, which is closely related with the control parameters of SVC and D-PMSGs-based wind farm. This type of control interaction will lead to sub-synchronous oscillation. Therefore, the influence of above control parameters on the oscillation characteristics is further studied here. The practical significance of this paper is indicating the necessity of coordinating and optimising control parameters in large-scale wind farm

Logging Pattern Detection by Multispectral Remote Sensing Imagery in North Subtropical Plantation Forests

Forest logging detection is important for sustainable forest management. The traditional optical satellite images with visible and near-infrared bands showed the ability to identify intensive timber logging. However, less intensive logging is still difficult to detect with coarse spatial resolution such as Landsat or high spatial resolution in fewer spectral bands. Although more high-resolution remote sensing images containing richer spectral bands can be easily obtained nowadays, the questions of whether they facilitate the detection of logging patterns and which spectral bands are more effective in detecting logging patterns, especially in selective logging, remain unresolved. Therefore, this paper aims to evaluate the combinations of visible, near-infrared, red-edge, and short-wave infrared bands in detecting three different logging intensity patterns, including unlogged (control check, CK), selective logging (SL), and clear-cutting (CC), in north subtropical plantation forests with the random forest algorithm using Sentinel-2 multispectral imagery. This study aims to explore the recognition performance of different combinations of spectral bands (visual (VIS) and near-infrared bands (NIR), VIS, NIR combined with red-edge, VIS, NIR combined with short-wave infrared bands (SWIR), and full-spectrum bands combined with VIS, NIR, red edge and SWIR) and to determine the best spectral variables to be used for identifying logging patterns, especially in SL. The study was conducted in Taizishan in Hubei province, China. A total of 213 subcompartments of different logging patterns were collected and the random forest algorithm was used to classify logging patterns. The results showed that full-spectrum bands which contain the red-edge and short-wave infrared bands improve the ability of conventional optical satellites to monitor forest logging patterns and can achieve an overall accuracy of 85%, especially for SL which can achieve 79% and 64% for precision and recall accuracy, respectively. The red-edge band (698–713 nm, B5 in Sentinel-2), short-wave infrared band (2100–2280 nm, B12 in Sentinel-2), and associated vegetation indices (NBR, NDre2, and NDre1) enhance the sensitivity of the spectral information to logging patterns, especially for the SL pattern, and the precision and recall accuracy can improve by 10% and 6%, respectively. Meanwhile, both clear-cutting and unlogged patterns could be well-classified whether adding a red-edge or SWIR band or both in VIS and NIR bands; the best precision and recall accuracies for clear-cutting were enhanced to 97%, 95% and 81%, 91% for unlogged, respectively. Our results demonstrate that the optical images have the potential ability to detect logging patterns especially for the clear-cutting and unlogged patterns, and the selective logging detection accuracy can be improved by adding red-edge and short-wave infrared spectral bands

A Numerical Simulation on the Leakage Event of a High-Pressure Hydrogen Dispenser

For the sake of the increasing demand of hydrogen fuel cell vehicles, there are more concerns on the safety of hydrogen refueling stations. As one of the key pieces of equipment, the hydrogen dispenser has drawn attention on this aspect since it involves massive manual operations and may be bothered by a high probability of failure. In this paper, a numerical study is conducted to simulate the possible leakage events of the hydrogen dispenser based on a prototype in China whose working pressure is 70 MPa. The leakage accident is analyzed with respect to leakage sizes, leak directions, and the time to stop the leakage. It is found that, due to the large mass flow rate under such high pressure, the leak direction and the layout of the components inside the dispenser become insignificant, and the ignitable clouds will form inside the dispenser in less than 1 s if there is a leakage of 1% size of the main tube. The ignitable clouds will form near the vent holes outside the dispenser, which may dissipate quickly if the leakage is stopped. On the other hand, the gas inside the dispenser will remain ignitable for a long time, which asks for a design with no possible ignition source inside. The results can be useful in optimizing the design of the dispenser, regarding the reaction time and sensitivity requirements of the leakage detector, the size and amount of vent holes, etc

Selective degradation of styrene-contained plastics catalyzed by iron under visible light

Efficient degradation of plastics, the vital challenge for a sustainable future, stands in need of better chemical recycling procedures that help produce commercially valuable small molecules and redefine plastic waste as a rich source of chemical feedstock. However, the corresponding chemical recycling methods, while being generally restricted to polar polymers, need improvement. Particularly, degradation of chemical inert nonpolar polymers, the major constitutes of plastics, are reported to have suffered from low selectivity and very harsh transformation conditions. Herein, we report an efficient method for the selective degradation of styrene-contained plastics under gentle conditions through oxidative multiple sp3 C-C bond cleavage. The unpresented procedure is catalyzed with inexpensive iron salts under visible light, using oxygen as the green oxidant. Furthermore, simple iron salts can be used to degrade plastics in the absence of solvent under natural conditions, highlighting the potential application of iron salts as additives for degradable plastics