Three-dimensional graphene nanosheets as cathode catalysts in standard and supercapacitive microbial fuel cell

© 2017 The Authors Three-dimensional graphene nanosheets (3D-GNS) were used as cathode catalysts for microbial fuel cells (MFCs) operating in neutral conditions. 3D-GNS catalysts showed high performance towards oxygen electroreduction in neutral media with high current densities and low hydrogen peroxide generation compared to activated carbon (AC). 3D-GNS was incorporated into air-breathing cathodes based on AC with three different loadings (2, 6 and 10mgcm−2). Performances in MFCs showed that 3D-GNS had the highest performances with power densities of 2.059±0.003Wm-2, 1.855±0.007Wm-2 and 1.503±0.005Wm-2 for loading of 10, 6 and 2mgcm−2 respectively. Plain AC had the lowest performances (1.017±0.009Wm-2). The different cathodes were also investigated in supercapacitive MFCs (SC-MFCs). The addition of 3D-GNS decreased the ohmic losses by 14–25%. The decrease in ohmic losses allowed the SC-MFC with 3D-GNS (loading 10mgcm−2) to have the maximum power (Pmax) of 5.746±0.186Wm-2. At 5mA, the SC-MFC featured an “apparent” capacitive response that increased from 0.027±0.007F with AC to 0.213±0.026F with 3D-GNS (loading 2mgcm−2) and further to 1.817±0.040F with 3D-GNS (loading 10mgcm−2)

Measuring Rice in Early-Childhood Education Activities: A Bridge Across Discrete and Continuous Magnitudes

In this study, we report on some qualitative results of an explorative study about how a sample of Italian children of ages 5 and 6 evaluate and manage quantities of rice, a substance that can be treated as continuous or discrete. In particular, we are interested in how young children manage the task of comparing quantities, judging whether there is “as much [rice] as” in different piles. Acknowledging the crucial role of artifacts both at a psychological and at a social level, we also offered the children different artifacts to face this task. Taking the Semiotic Mediation perspective, we analyze the strategies and the situated signs developed by the children, identifying those that could later be used by a teacher as pivot signs when constructing the mathematical meanings associated with the process of measurement

Effect of surface phosphorus functionalities of activated carbons containing oxygen and nitrogen on electrochemical capacitance

Micro/mesoporous activated carbons containing oxygen and phosphorus heteroatoms were modified by incorporation of nitrogen using melamine and urea precursors. The surface chemistry was analyzed by the means of elemental analysis, XPS, and 31P MAS NMR. The results indicate that upon the incorporation of nitrogen at high temperatures not only new species involving carbon/nitrogen/oxygen are formed but also the phosphorous environment is significantly altered. Both urea and melamine precursors have similar effects on formation of P–N and P–C bonds. These compounds, although present in small but measurable quantities seem to affect the performance of carbons in electrochemical capacitors. With an increase in the heterogeneity of phosphorus containing species and with a decrease in the content pyrophosphates the capacitance increases and the retention ratio of the capacitor is improved