Nitrogen-doped carbon materials featuring atomically dispersed metal cations (M–N–C) are an emerging family of materials with potential applications for electrocatalysis. The electrocatalytic ...activity of M–N–C materials toward four-electron oxygen reduction reaction (ORR) to H2O is a mainstream line of research for replacing platinum-group-metal-based catalysts at the cathode of fuel cells. However, fundamental and practical aspects of their electrocatalytic activity toward two-electron ORR to H2O2, a future green “dream” process for chemical industry, remain poorly understood. Here we combined computational and experimental efforts to uncover the trends in electrochemical H2O2 production over a series of M–N–C materials (M = Mn, Fe, Co, Ni, and Cu) exclusively comprising atomically dispersed M–N x sites from molecular first-principles to bench-scale electrolyzers operating at industrial current density. We investigated the effect of the nature of a 3d metal within a series of M–N–C catalysts on the electrocatalytic activity/selectivity for ORR (H2O2 and H2O products) and H2O2 reduction reaction (H2O2RR). Co–N–C catalyst was uncovered with outstanding H2O2 productivity considering its high ORR activity, highest H2O2 selectivity, and lowest H2O2RR activity. The activity–selectivity trend over M–N–C materials was further analyzed by density functional theory, providing molecular-scale understandings of experimental volcano trends for four- and two-electron ORR. The predicted binding energy of HO* intermediate over Co–N–C catalyst is located near the top of the volcano accounting for favorable two-electron ORR. The industrial H2O2 productivity over Co–N–C catalyst was demonstrated in a microflow cell, exhibiting an unprecedented production rate of more than 4 mol peroxide gcatalyst –1 h–1 at a current density of 50 mA cm–2.
Abstract
Proton exchange membrane fuel cells have been recently developed at an increasing pace as clean energy conversion devices for stationary and transport sector applications. High platinum ...cathode loadings contribute significantly to costs. This is why improved catalyst and support materials as well as catalyst layer design are critically needed. Recent advances in nanotechnologies and material sciences have led to the discoveries of several highly promising families of materials. These include platinum-based alloys with shape-selected nanostructures, platinum-group-metal-free catalysts such as metal-nitrogen-doped carbon materials and modification of the carbon support to control surface properties and ionomer/catalyst interactions. Furthermore, the development of advanced characterization techniques allows a deeper understanding of the catalyst evolution under different conditions. This review focuses on all these recent developments and it closes with a discussion of future research directions in the field.
While the development of digital technologies provides generous resources for educational practices, how the use of information and communication technology (ICT) supports instructional reforms in ...schools still needs further exploration. The purpose of the study is to understand the roles of school leaders and teachers play in an instructional reform supported by ICT as well as how these roles interact with each other. The study selected a Chinese middle‐high school that successfully had a school‐wide instructional reform supported by ICT as an exemplary case and collected data through document analysis, interviews and observations. The results indicated that the school leadership was critical in the instructional reform. While the executive vice principal was in an essential position as an initiator and strategic planner, the leadership was distributed and stretched over in the school. The school built supporting pedagogical and organizational systems for continuous and collaborative learning and helped the teachers develop four new roles: learners, facilitators to student‐centered learning, collaborators and researchers.
Conversion of calcium carbonate (calcite; CC) to hydroxyapatite (HAp) was examined when the CC particles of sub μm size were soaked at 37 °C for up to 10 d in 0.15 M K
2
HPO
4
(20 ml), whose pH was ...set to 3-12. Here, the solution contained amino acids, such as glutamine (Glu), arginine (Arg), and glycine (Gly), and their content varied from 0-1.0 g per ml of solution. From the X-ray diffraction (XRD) intensity of the 104 and 211 diffractions of calcite and apatite, respectively, it was seen that the presence of the amino acids promoted the conversion. This was supported by the thermogravimetry (TG) results. The highest promotion was observed at 0.5 g addition of amino acids to the phosphate solution, while Glu showed the highest promotion among the amino acids and Gly the lowest. A scanning electron microscopy study indicated that petal-like HAp nano-crystallites covered the entire surface of the CC particles when they were soaked in the phosphate solution with 0.1 g or more of amino acid for 10 d. The XRD intensity ratio 104(CC)/211(HAp) indicated greater CC to HAp conversion in the solutions at pH 3 and 6 than in the more alkaline solutions. This was attributed to the dissolution of CC in the acidic solutions, which was confirmed by bubbling in these solutions.
Conversion of calcium carbonate (calcite; CC) to hydroxyapatite (HAp) was examined when the CC particles of sub μm size were soaked at 37 °C for up to 10 d in 0.15 M K
2
HPO
4
(20 ml), whose pH was set to 3-12.
A forest fire susceptibility map generated with the fire susceptibility model is the basis of fire prevention resource allocation. A more reliable susceptibility map helps improve the effectiveness ...of resource allocation. Thus, further improving the prediction accuracy is always the goal of fire susceptibility modeling. This paper developed a forest fire susceptibility model based on an ensemble learning method, namely light gradient boosting machine (LightGBM), to produce an accurate fire susceptibility map. In the modeling, a subtropical national forest park in the Jiangsu province of China was used as the case study area. We collected and selected eight variables from the fire occurrence driving factors for modeling based on correlation analysis. These variables are from topographic factors, climatic factors, human activity factors, and vegetation factors. For comparative analysis, another two popular modeling methods, namely logistic regression (LR) and random forest (RF) were also applied to construct the fire susceptibility models. The results show that temperature was the main driving factor of fire in the area. In the produced fire susceptibility map, the extremely high and high susceptibility areas that were classified by LR, RF, and LightGBM were 5.82%, 18.61%, and 19%, respectively. The F1-score of the LightGBM model is higher than the LR and RF models. The accuracy of the model of LightGBM, RF, and LR is 88.8%, 84.8%, and 82.6%, respectively. The area under the curve (AUC) of them is 0.935, 0.918, and 0.868, respectively. The introduced ensemble learning method shows better ability on performance evaluation metrics.
Inflammation had showed its important role in the pathogenesis of cerebral ischemia and secondary damage. Safflower yellow B (SYB) had neuroprotective effects against oxidative stress-induced brain ...injuries, but the mechanisms were still largely unknown to us. In this study, we tried to investigate the anti-inflammation effects of SYB and the possible roles of AMPK/NF-κB signaling pathway on these protective effects. In vivo, brain ischemia/reperfusion (I/R) was induced by transient middle cerebral artery occlusion for 2 h and reperfusion for 20 h. Neurofunctional evaluation, infarction area, and brain water contents were measured. Brain injury markers and inflammatory cytokines levels were measured by ELISA kits. In vitro, cell viability, apoptosis, and LDH leakage were measured after I/R in PC12 cells. The expression and phosphorylation levels of AMPK, NF-κB p65, and P-IκB-α in cytoplasm and nuclear were measured by Western blotting. SiRNA experiment was performed to certify the role of AMPK. The results showed SYB reduced infarct size, improved neurological outcomes, and inhibited brain injury after I/R. In vitro test, SYB treatment alleviated PC12 cells injury and apoptosis and inhibited the inflammatory cytokines (IL-1, IL-6, TNF-α, and COX-2) in a dose-dependent manner. SYB treatment induced AMPK phosphorylation and inhibited NF-κB p65 nuclear translocation both in brain and in PC12 cells. Further studies also showed that the inhibition of NF-κB activity of SYB was through AMPK. In conclusion, SYB protected brain I/R injury through reducing expression of inflammatory cytokines and this effect might be partly due to the inhibition of NF-κB mediated by AMPK.
Effective photosensitizers are of particular importance for the widespread clinical utilization of phototherapy. However, conventional photosensitizers are usually plagued by short-wavelength ...absorption, inadequate photostability, low reactive oxygen species (ROS) quantum yields, and aggregation-caused ROS quenching. Here, we report a near-infrared (NIR)-supramolecular photosensitizer (RuDA) via self-assembly of an organometallic Ru(II)-arene complex in aqueous solution. RuDA can generate singlet oxygen (
O
) only in aggregate state, showing distinct aggregation-induced
O
generation behavior due to the greatly increased singlet-triplet intersystem crossing process. Upon 808 nm laser irradiation, RuDA with excellent photostability displays efficient
O
and heat generation in a
O
quantum yield of 16.4% (FDA-approved indocyanine green: Φ
= 0.2%) together with high photothermal conversion efficiency of 24.2% (commercial gold nanorods: 21.0%, gold nanoshells: 13.0%). In addition, RuDA-NPs with good biocompatibility can be preferably accumulated at tumor sites, inducing significant tumor regression with a 95.2% tumor volume reduction in vivo during photodynamic therapy. This aggregation enhanced photodynamic therapy provides a strategy for the design of photosensitizers with promising photophysical and photochemical characteristics.
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