The environmentally friendly synthesis of highly active Fe‐N‐C electrocatalysts for proton‐exchange membrane fuel cells (PEMFCs) is desirable but remains challenging. A simple and scalable method is ...presented to fabricate FeII‐doped ZIF‐8, which can be further pyrolyzed into Fe‐N‐C with 3 wt % of Fe exclusively in Fe‐N4 active moieties. Significantly, this Fe‐N‐C derived acidic PEMFC exhibits an unprecedented current density of 1.65 A cm−2 at 0.6 V and the highest power density of 1.14 W cm−2 compared with previously reported NPMCs. The excellent PEMFC performance can be attributed to the densely and atomically dispersed Fe‐N4 active moieties on the small and uniform catalyst nanoparticles.
An environmentally friendly, facile, low‐cost, and scalable solid‐phase synthesis was developed for a highly active Fe‐N‐C electrocatalyst with iron exclusively in Fe‐N4 moieties. The as‐prepared Fe2‐Z8‐C delivered an unprecedented power density of 1.14 W cm−2 in acidic proton‐exchange membrane fuel cell, which was attributed to the densely and atomically dispersed Fe‐N4 active moieties and the small catalyst nanoparticles.
Porous carbon nanotubes/cobalt nanoparticles (CNTs/Co) composite with dodecahedron morphology was synthesized by in situ pyrolysis of the Co-based zeolitic imidazolate framework in a reducing ...atmosphere. The morphology and microstructure of the composite can be well tuned by controlling the pyrolysis conditions. At lower pyrolysis temperature, the CNTs/Co composite is composed of well-dispersed Co nanoparticles and short CNT clusters with low graphitic degree. The increase of pyrolysis temperature/time promotes the growth and graphitization of CNTs and leads to the aggregation of Co nanoparticles. The optimized CNTs/Co composite exhibits strong dielectric and magnetic losses as well as a good impedance matching property. Interestingly, the CNTs/Co composite displays extremely strong electromagnetic wave absorption with a maximum reflection loss of −60.4 dB. More importantly, the matching thickness of the absorber is as thin as 1.81 mm, and the filler loading of composite in the matrix is only 20 wt %. The highly efficient absorption is closely related to the well-designed structure and the synergistic effect between CNTs and Co nanoparticles. The excellent absorbing performance together with lightweight and ultrathin thickness endows the CNTs/Co composite with the potential for application in the electromagnetic wave absorbing field.
Simultaneously increasing the activity and stability of the single-atom active sites of M-N-C catalysts is critical but remains a great challenge. Here, we report an Fe-N-C catalyst with ...nitrogen-coordinated iron clusters and closely surrounding Fe-N
active sites for oxygen reduction reaction in acidic fuel cells. A strong electronic interaction is built between iron clusters and satellite Fe-N
due to unblocked electron transfer pathways and very short interacting distances. The iron clusters optimize the adsorption strength of oxygen reduction intermediates on Fe-N
and also shorten the bond amplitude of Fe-N
with incoherent vibrations. As a result, both the activity and stability of Fe-N
sites are increased by about 60% in terms of turnover frequency and demetalation resistance. This work shows the great potential of strong electronic interactions between multiphase metal species for improvements of single-atom catalysts.
Trimethylamine N-oxide (TMAO) is an oxidation product of trimethylamine (TMA) and is present in many aquatic foods. Here, we investigated the effects of TMAO on glucose tolerance in high fat diet ...(HFD)-fed mice. Male C57BL/6 mice were randomly assigned to the control, high fat (HF), and TMAO groups. The HF group was fed a diet containing 25% fat, and the TMAO group was fed the HFD plus 0.2% TMAO for 4 weeks. After 3 weeks of feeding, oral glucose tolerance tests were performed. Dietary TMAO increased fasting insulin levels and homeostasis model assessment-estimated insulin resistance (HOMA-IR) and exacerbated the impaired glucose tolerance in HFD-fed mice. These effects were associated with the expression of genes related to the insulin signal pathway, glycogen synthesis, gluconeogenesis and glucose transport in liver. mRNA levels of the pro-inflammatory cytokine MCP-1 increased significantly and of the anti-inflammatory cytokine IL-10 greatly decreased in adipose tissue. Our results suggest that dietary TMAO exacerbates impaired glucose tolerance, obstructs the hepatic insulin signaling pathway, and causes adipose tissue inflammation in mice fed a high fat diet.
Non-precious-metal or metal-free catalysts with stability are desirable but challenging for proton exchange membrane fuel cells. Here we partially unzip a multiwall carbon nanotube to synthesize ...zigzag-edged graphene nanoribbons with a carbon nanotube backbone for electrocatalysis of oxygen reduction in proton exchange membrane fuel cells. Zigzag carbon exhibits a peak areal power density of 0.161 W cm
and a peak mass power density of 520 W g
, superior to most non-precious-metal electrocatalysts. Notably, the stability of zigzag carbon is improved in comparison with a representative iron-nitrogen-carbon catalyst in a fuel cell with hydrogen/oxygen gases at 0.5 V. Density functional theory calculation coupled with experimentation reveal that a zigzag carbon atom is the most active site for oxygen reduction among several types of carbon defects on graphene nanoribbons in acid electrolyte. This work demonstrates that zigzag carbon is a promising electrocatalyst for low-cost and durable proton exchange membrane fuel cells.
Over the last several years, piezo-photocatalytic effect was intensively investigated for a facile, effective and promising protocol to sewage treatment and environmental remediation. The research on ...the integration of piezocatalytic and photocatalytic process on lead-free ferroelectric materials is highly demanded to further push this field forward. In this work, BaTiO3 nanowires (BT NWs) were fabricated by a two-step hydrothermal method. The degradation of organic dye (methyl orange, MO) aqueous solution (5 mg L−1) by integrating photocatalysis with the piezoelectric-like effect under UV light radiation and ultrasonic vibration was investigated. The decomposition ratio reaches up to ∼98.17% (at 80 min), which is around 1.28 and 2.24 times of the sole piezocatalysis and photocatalysis process, respectively. The intermediate product of hydroxyl radical (•OH) and superoxide radical (•O2−) was detected and quantified by radical trapping experiments, to illustrating their key role in degrading MO molecules. In addition, we carried out sequential cycles to evaluate the cycling stability and usage durability of catalysts and a reduction of ∼15% in the efficiency was observed after four cycles. This work provides a promising paradigm for the further development of piezo-photocatalytic materials and target applications in environmental field.
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•BT NWs were prepared by a two-step hydrothermal method.•The synergistic piezo-photocatalysis realizes the efficient degradation of dyes.•Degradation rate of piezo-photocatalysis is 1.28 and 2.24 times of sole piezocatalysis and photocatalysis, respectively.•The mechanism of piezo-photocatalysis was detailed.
Bronchiectasis revealed by chest computed tomography in COPD patients and its comorbid effect on prognosis have not been addressed by large-sized studies. Understanding the presence of bronchiectasis ...in COPD is important for future intervention and preventing disease progression.
Observational studies were identified from electronic literature searches in Cochrane library, PubMed, ScienceDirect databases, American Thoracic Society and European Respiratory Society meeting abstracts. A systematic review and meta-analysis of studies was performed to summarize the factors associated with bronchiectasis in COPD patients. Primary outcomes included the risks for exacerbation frequency, isolation of a potentially pathogenic microorganism, severe airway obstruction and mortality. Odds ratios (ORs) were pooled by random effects models.
Fourteen observational studies were eligible for the study. Compared with COPD without bronchiectasis, comorbid bronchiectasis in COPD increased the risk of exacerbation (1.97, 95% CI, 1.29-3.00), isolation of a potentially pathogenic microorganism (4.11, 95%CI, 2.16-7.82), severe airway obstruction (1.31, 95% CI, 1.09-1.58) and mortality (1.96, 95% CI, 1.04-3.70).
The presence of bronchiectasis in patients with COPD was associated with exacerbation frequency, isolation of a potentially pathogenic microorganism, severe airway obstruction and mortality.
The response of the catalyst oxygen reduction reaction (ORR) activity to temperature is an important basis for identifying and selecting ORR catalysts which include platinum group metal (PGM) ...catalysts and PGM-free catalysts (including nonprecious metal catalysts and metal-free catalysts). Rotating disk electrode (RDE) technology is the most commonly used method for assessing ORR activity. Herein, the ORR activity parameters of three representative catalysts Pt/C, Fe–N–C, and N/P-doped carbon nanomaterials were measured by the RDE technique over a wide temperature range of 0–80 °C for the first time. Experimental results indicate that due to the significant decrease in oxygen concentration with increasing temperature, Pt/C exhibits the highest activity at ∼4 °C, while Fe–N–C and N/P–C achieve optimum performances at ∼40 and 60 °C respectively, at which the ORR kinetics and oxygen concentration in electrolyte are balanced.
The bidirectional cell-to-cell equalization methods perform well to prevent the series-connected batteries from overcharging and undercharging. However, it remains a challenge to achieve fast ...equalization and high equalization efficiency with low complexity. To address the issue, we propose a new bidirectional cell-to-cell active equalization method using a multiwinding transformer. The new method allows the energy to transfer directly from the highest voltage cell to the lowest one by fly-back operation or forward operation which gives a short balancing path and guarantees a fast equalization speed. We adopt the bidirectional switches of low conduction loss for high equalization efficiency. Since the bidirectional switches are turned on or off simultaneously, a common driving circuit for the bidirectional switch has been designed to reduce the number of the driving circuits by half. The experiments with a six 50-Ah Lithium-ion battery strings are conducted and the results have demonstrated that our new approach has achieved a good overall performance of equalization in terms of speed, efficiency, and complexity of the circuit.
Natural alginate fibers are used as templates to fabricate CoFe alloy-decorated hierarchically porous carbon fibers (HPCFs). Due to the coordination with negatively charged α−L−guluronate blocks, ...transition metal (TM) ions could be confined in the “egg box” structure of alginate, which convert to CoFe alloy particles that homogenously embedded in HPCFs during carbonization. The composition and weight ratio of magnetic particles could be well controlled by adjusting the absorbed TM ions and carbonization temperature. Unlike previous analogues with uniform mesopores, this composite fiber simultaneously possesses a number of mesopores and a high proportion of submicron macropores which not only facilitates the accommodation of large-sized CoFe particles, but also induces abundant interfacial polarization and EMW multi-scattering. Remarkably, the CoFe/HPCF with a filler loading as low as 15 wt% in matrix achieves an extremely strong reflection loss of −69.1 dB at a thin thickness of 1.6 mm, and its effective absorption bandwidth reaches 5.2 GHz, showing better comprehensive properties than other similar absorbers. This work highlights the importance of hierarchically porous structure (especially macroporous structure) on improving EMW absorption. The synthetic strategy is green, low cost, scalable, and can be used to synthesize other highly efficient composite absorbers.
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