Experimental and analytical analysis of polarization and water transport behaviors of hydrogen alkaline membrane fuel cell

Experimental test and analytical modeling are conducted to investigate the operating behavior of an alkaline electrolyte membrane (AEM) fuel cell fed by H2/air (or O2) and explore the effect of various operating pressures on the water transfer mechanism. According to the experimental test, the cell performance is greatly improved through increasing the operating pressure gradient from anode to cathode which leads to significant liquid water permeation through the membrane. The high frequency resistance of the A901 alkaline membrane is observed to be relatively stable as the operating pressure varies based on the electrochemical impedance spectroscopy (EIS) method. Correspondingly, based on the modeling prediction, the averaged water content in the membrane electrode assembly (MEA) does not change too much which leads to the weak variation of membrane ohmic resistance. This reveals that the performance enhancement should give the credit to better electro-chemical reaction kinetics for both the anode and cathode, also prone by the EIS results. The reversion of water back diffusion direction across the membrane is also observed through analytical solution

Comment on “Comparison of Methods for Estimating Critical Properties of Alkyl Esters and Its Mixtures”

Comment on “Comparison of Methods for Estimating Critical Properties of Alkyl Esters and Its Mixtures

Variation of Critical Crystallization Pressure for the Formation of Square Ice in Graphene Nanocapillaries

Two-dimensional square ice in graphene nanocapillaries at room temperature is a fascinating phenomenon and has been confirmed experimentally. Instead of the temperature for bulk ice, the high van der Waals pressure becomes an all-important factor to induce the formation of square ice and needs to be studied further. By all-atom molecular dynamics simulations of water confined between two parallel graphene sheets, which are changed in size (the length and the width of the graphene sheets) over a wide range, we find that the critical crystallization pressure for the formation of square ice in the nanocapillary strongly depends on the size of the graphene sheet. The critical crystallization pressure slowly decreases as the graphene size increases, converging to an approximately macroscopic crystallization pressure. The unfreezable threshold for graphene size is obtained by estimating the actual pressure, and it is difficult to form the square ice spontaneously in practice when the graphene sheet is smaller than the threshold. Moreover, the critical crystallization pressure fluctuates when the graphene size is minuscule, and the range of oscillation narrows as the sheet size increases, converging to the macroscopic behavior of a single critical icing pressure for large sheets. The graphene size also affects the stability and crystallization time of the square ice

Eumelanin-like Poly(levodopa) Nanoscavengers for Inflammation Disease Therapy

In the current years, polydopamine nanoparticles (PDA NPs) have been extensively investigated as an eumelanin mimic. However, unlike natural eumelanin, PDA NPs contain no 5,6-dihydroxyindole-2-carboxylic acid (DHICA)-derived units and may be limited in certain intrinsic properties; superior eumelanin-like nanomaterials are still actively being sought. Levodopa (l-DOPA) is a natural eumelanin precursor and expected to convert into DHICA and further remain within the final product through covalent or physical interactions. Herein, poly(levodopa) nanoparticles [P(l-DOPA) NPs] were synthesized with the assistance of zinc oxide as a supplement to synthetic eumelanin. This study found that P(l-DOPA) NPs had ∼90% DHICA-derived subunits on their surface and exhibited superior antioxidant activity compared to PDA NPs due to their looser polymeric microstructure. Benefitting from a stronger ROS scavenging ability, P(l-DOPA) NPs outperformed PDA NPs in treating cellular oxidative stress and acute inflammation. This research opens up new possibilities for the development and application of novel melanin-like materials

Metabolic disorders among 3814 Beijing children aged 10–18 years by weight status, subsample of BCAMS sample population (n = 3814).^*

<p>Abbreviation: WC, waist circumference; SBP, systolic blood pressure; DBP, diastolic blood pressure; HDL-C, high-density lipoprotein cholesterol; FPG, fasting plasma glucose; TG: fasting serum triglyceride.</p>*<p>Within the whole BCAMS sample, a subsample of 3814 children aged 10–18 years was recruited for venipuncture blood samples. Weight status was defined for the subsample of 3814 children based on the International Obesity Task Force (IOTF) BMI cutoffs; Mean and SD were calculated using covariance analysis adjusted for age and sex.</p>a<p><i>P</i> values for trend tests across weight status groups adjusted for age and gender.</p

Oxygen transport in proton exchange membrane fuel cells with metal foam flow fields

Metal foam flow fields have shown great potential in improving the performance of proton exchange membrane (PEM) fuel cells, while their effect on the oxygen transport process remains inadequately understood. In this study, oxygen transport in metal foam flow fields (under zero-humidity operating conditions) is simulated by using a three-dimensional multi-species lattice Boltzmann model. Comparison is done between the metal foam flow field and the conventional channel-rib flow field, and parametric studies are conducted on the metal foam porosity, pore density, and compression ratio. Results show that the metal foam flow field enhances mass transfer of oxygen to the catalyst layer and improves the oxygen distribution homogeneity. Within the range of parameters considered, decrease in the metal foam porosity yields nonmonotonic variation of the mass transfer rate of oxygen to the catalyst layer, which increases at high inlet velocities (higher than 2 m/s) but decreases at low inlet velocities (less than 2 m/s). The increase in metal foam pore density and compression ratio leads to enhanced mass transfer of oxygen, which becomes increasingly prominent at high inlet velocity. The results of this study could be insightful for the implementation of metal foam flow fields in PEM fuel cells

Logistic regression model: odds ratios (OR) and 95%CIs of CVD risk factors according to the degree and type of obesity among Beijing children aged 6–18 years, whole BCAMS sample (n = 19593).

<p>Abbreviation: TG, triglyceride; TC, total cholesterol; IFG, impaired fasting glucose. TG, TC and fasting blood glucose were tested based on fasting finger capillary blood.</p>a<p>Degree of obesity was diagnosed based on International Obesity Task Force (IOTF) BMI cutoffs; Subjects defined as normal weight was used as reference group, and controlled for age and sex.</p>b<p>Type of obesity was diagnosed simultaneously by IOTF-BMI criteria and the age-,sex-specific waist circumference references for Chinese children and adolescents; Subjects who did not have general obesity or central obesity were used as the reference group.</p>c<p>Hypertension was defined as systolic and/or diastolic blood pressure ≥95th percentile, the new Chinese reference.</p>d<p>Elevated TG was defined as TG≥1.7 mmol/L.</p>e<p>Elevated TC was defined as TC≥5.2 mmol/L.</p>f<p>IFG was defined as the fasting capillary glucose l≥5.6 mmol/L.</p>*<p>None had this metabolic disorder.</p

Prevalence (%) of obesity and metabolic disorders among Beijing children aged 6–18 years, whole BCAMS sample. population.

<p>Abbreviation: TG, triglyceride; TC, total cholesterol; IFG, impaired fasting glucose. TG, TC and fasting blood glucose were tested based on fasting finger capillary blood.</p>a<p>Overweight and obesity were diagnosed based on International Obesity Task Force (IOTF) BMI cutoffs.</p>b<p>Diagnosed by systolic and/or diastolic (K4) blood pressure ≥90th percentile for age and sex from the blood pressure reference standards for Chinese children and adolescents. High-normal was defined as systolic and/or diastolic blood pressure ≥90th–<95th percentile; hypertension ≥95th percentile for age and gender.</p>c<p>Elevated TG was diagnosed as TG≥1.7 mmol/L.</p>d<p>Elevated TC was diagnosed as TC≥5.2 mmol/L.</p>e<p>IFG was diagnosed as glucose ≥5.6 mmol/L.</p>*<p>χ2-test, all rural and urban differences were significant, <i>P</i><0.01;</p

Logistic regression models; Odds ratio (OR) and 95%CIs of MetS and MetS component for Beijing adolescents aged 10–18 years according to the degree and type of obesity, subsample^* of BCAMS population (n = 3814).

<p>Abbreviation: HDL-C, high-density lipoprotein cholesterol; IFG, impaired fasting glucose; TG, triglyceride; BP, blood pressure; MetS, metabolic syndrome.</p>*<p>Within the whole BCAMS sample, a subsample of 3814 children aged 10–18 years was recruited for venipuncture blood samples.</p>a<p>Degree of obesity was diagnosed based on International Obesity Task Force (IOTF) BMI cutoffs; normal weight subjects were used as reference group; all models adjusted for age and gender.</p>b<p>Type of obesity was diagnosed simultaneously by IOTF-BMI criteria and the age-,sex-specific waist circumference references for Chinese children and adolescents; subjects who were neither general obesity nor central obesity were used as the reference group; all models adjusted for age and gender.</p>c<p>MetS and its components were diagnosed according to the IDF criteria for adolescents: For adolescents aged 10∼15, MetS was diagnosed with central obesity (waist circumference ≥90th percentile for age and gender by the Chinese reference; and the presence of any two of the following four factors, ie: elevated BP (systolic ≥130/diastolic ≥85 mmHg), low HDL-C (<1.03 mmol/L), elevated TG (≥1.7 mmol/L ), IFG (fasting plasma glucose ≥5.6 mmol/L). For children aged 16 years or older, MetS was diagnosed using IDF criteria for adults, ie: Central obesity (WC≥90 cm for Chinese men and ≥80 cm for Chinese women) plus any two of the following four factors: elevated BP (systolic ≥130/diastolic ≥85 mmHg), low HDL-C (<1.03 mmol/L in males and <1.29 mmol/L in females), elevated TG (≥1.7 mmol/L), IFG (fasting plasma glucose (FPG) ≥5.6 mmol/L).</p>#<p>None had the MetS component.</p

Prevalence (%) of metabolic syndrome by the degree and type of obesity (n = 3814) ^a.

<p>^a Metabolic syndrome was diagnosed by IDF criteria for adolescents; For adolescents aged 10 years to younger than 16 years, MetS was diagnosed with central obesity (WC≥90th percentile) for age and sex by the Chinese reference; and the presence of any two of the following four factors, ie. elevated BP (systolic ≥130/diastolic ≥85 mmHg), low HDL-C (<1.03 mmol/L), elevated TG (≥1.7 mmol/L ), IFG (fasting plasma glucose ³ 5.6 mmol/L). For children aged 16 years or older, MetS was diagnosed using IDF criteria for adults, ie: Central obesity (WC≥90 cm for Chinese men and ≥80 cm for Chinese women) plus any two of the following four factors: elevated BP (systolic ≥130/diastolic ≥85 mmHg), low HDL-C (<1.03 mmol/L in males and <1.29 mmol/L in females), elevated TG (≥1.7 mmol/L), IFG (fasting plasma glucose (FPG)≥5.6 mmol/L). ^b Degree of obesity was diagnosed based on International Obesity Task Force (IOTF) BMI cutoffs. ^c Type of obesity was diagnosed simultaneously by IOTF-BMI criteria and the age-,sex-specific waist circumference 90th percentile by the Chinese reference.</p