Distribution of current density across the active area at various stoichiometry ratios using the JRC ZERO∇CELL single cell PEM fuel cell testing hardware

The performance of the PEM fuel cell directly depends on the partial pressure of provided reactants, namely hydrogen and oxygen. Since reactants are consumed in the fuel cell reaction, partial pressure of reactants decreases in the direction of reactants flow. This well-known mechanism makes the performance of the fuel cell dependent on the stoichiometry ratios of input reactants. The JRC ZERO∇CELL, a single cell PEM fuel cell testing setup, is developed to provide as much as possible uniform operating conditions at the 10cm2 active area specimen, hence giving uniform current density across the active area of the cell. To investigate what is the real gradient of current density across the active area for the JRC ZERO∇CELL at various reactant stoichiometry ratios, segmented bi-polar plates and current collectors are developed. This study presents experimental investigation of the current density distribution across the active area of the JRC ZERO∇CELL setup at range of reactant stoichiometry ratios from λ = 2 up to λ = 15. Current density gradients are considered along the gas flow as well as in the transverse direction. The experimental results show that the current density gradient across the active area, although dependant on the reactants stoichiometry ratios, is relatively small as compared with a wide range of investigated stoichiometry ratios.

The soil bacterial and fungal diversity were determined by the stoichiometric ratios of litter inputs: evidence from a constructed wetland

Plant litter is an important component in wetland ecosystems, and the role of plant litter decomposition is considered to be important for wetland ecosystem functions and services. However, the consequences of litter inputs have seldom been experimentally tested in real ecosystems such as constructed wetlands (CWs). The enriched nutrients in CWs might weaken the role of litter inputs on soil carbon and nitrogen cycling. Here, we conducted a two-month field experiment to examine the effects of litter inputs on the soils in CWs. Our results showed that litter inputs significantly affected soil microbial (bacterial and fungi) diversities and properties (soil total nitrogen and nitrogen isotopes), and litter species with higher stoichiometry ratios, i.e. C/N, C/P and N/P led to higher microbial diversities. However, litter species had no or weak effects on microbial activities (CO2 and CH4 flux) or on the relative abundance of microbial communities, indicating that other environmental factors in such a CW might have stronger effects on those factors than litter inputs. These results highlighted the importance of submerged plant litter in nutrient-rich wetland ecosystems and provide potential tools for managers to improve the ecosystem functions and/or services via altering microbial diversities.

Shrub Encroachment Shapes Soil Nutrient Concentration, Stoichiometry and Carbon Storage in an Abandoned Subalpine Grassland

Soil nutrient stoichiometry plays a substantial role in terrestrial carbon and nutrient cycling. However, the changes in soil nutrient stoichiometry with shrub encroachment (SE) remain poorly understood, especially in subalpine areas. We examined the changes in soil nutrient concentration, nutrient stoichiometry, and organic carbon (OC) storage (at a depth of 0–5, 5–10 and 10–20 cm) in three successional shrub encroachment stages (early, mid and late) in an abandoned subalpine Eulalia pallens (Hackel) Kuntze grassland. An ANOVA showed that SE did not produce serious soil acidification, but significantly increased the soil OC and total phosphorous (TP) concentration, and improved the stoichiometry ratio of soil OC to total nitrogen (OC:TN) in all layers. OC storage tended to increase with SE. SE thus did not indicate degradation of the grassland. A redundancy analysis (RDA) and partial RDA revealed that the shrub relative cover and soil water content were the most important factors affecting the soil nutrient concentration, that the soil available phosphorous (AP), nitrogen, potassium, calcium (ACa), and magnesium concentration and shrub relative cover were the most important factors influencing soil nutrient stoichiometry ratios, and that soil OC:TN, TN:TP, OC:TN:TP, and AP:ACa ratios, bulk density, and pH were the most important factors influencing soil OC storage over SE. Our study provides insights into SE in grassland areas, and potentially provides a useful reference for ongoing grassland conservation and restoration in subalpine regions.

The role of stoichiometry in superconducting Nb1−βSnβ: electronic and vibrational properties from ab initio calculations

Using first principles calculations the electronic, vibrational and superconducting properties of Nb3Sn compounds with different stoichiometry ratios in the A15 phase have been studied.