Modular Design of Highly Active Unitized Reversible Fuel Cell Electrocatalysts

A modular, multicomponent catalyst design principle is introduced and exemplified using a three-component, oxygen reduction reaction/oxygen evolution reaction (ORR/OER) catalyst designed for the oxygen electrode of unitized reversible fuel cells (URFCs). The catalyst system exhibited unprecedented catalytic performance in liquid electrolyte and in single unitized reversible fuel cell tests. The distinct components, each active for either ORR or OER, are prepared and optimized independently of each other and physically mixed during electrode preparation. The new modular URFC catalyst, Cu-α-MnO2/XC-72R/NiFe-LDH, combined a carbon-supported, Cu-stabilized α-MnO2 ORR catalyst with a NiFe-LDH OER catalyst and displayed improved activity and stability under URFC cycling compared to platinum group metal references. Stepwise modular optimization of the carbon and the interlayer anions of the OER component led to a further improved derivative, Cu-α-MnO2/O-MWCNTs/NiFe-LDH-Cl–. This URFC catalyst outperformed all previous materials in terms of its combined overpotential ηORR-OER and performance stability in the rotating disk electrode (RDE) scale. Its single-cell performance is analyzed and discussed

The Use of the Cancellation Technique to Quantify the Hermann Grid Illusion

When observers view a grid of mid-gray lines superimposed on a black background, they report seeing illusory dark gray smudges at the grid intersections, an effect known as the Hermann grid illusion. The strength of the illusion is often measured using the cancellation technique: A white disk is placed over one of these intersections and the luminance of the disk is reduced until the disk disappears. Its luminance at this point, i.e., the disk's detection threshold, is taken to be a measure of the strength of the illusion. Our experiments showed that some distortions of the Hermann grid, which were sufficient to completely disrupt the illusion, did not reduce the disk's detection threshold. This showed that the cancellation technique is not a valid method for measuring the strength of the Hermann grid illusion. Those studies that attempted to use this technique inadvertently studied a different effect known as the blanking phenomenon. We conclude by presenting an explanation for the latter effect

Atomically dispersed Pt-N-4 sites as efficient and selective electrocatalysts for the chlorine evolution reaction

Chlorine evolution reaction (CER) is a critical anode reaction in chlor-alkali electrolysis. Although precious metal-based mixed metal oxides (MMOs) have been widely used as CER catalysts, they suffer from the concomitant generation of oxygen during the CER. Herein, we demonstrate that atomically dispersed Pt-N-4 sites doped on a carbon nanotube (Pt-1/CNT) can catalyse the CER with excellent activity and selectivity. The Pt-1/CNT catalyst shows superior CER activity to a Pt nanoparticle-based catalyst and a commercial Ru/Ir-based MMO catalyst. Notably, Pt-1/CNT exhibits near 100% CER selectivity even in acidic media, with low Cl- concentrations (0.1M), as well as in neutral media, whereas the MMO catalyst shows substantially lower CER selectivity. In situ electrochemical X-ray absorption spectroscopy reveals the direct adsorption of Cl- on Pt-N-4 sites during the CER. Density functional theory calculations suggest the PtN4C12 site as the most plausible active site structure for the CER

On the Functional Significance of the P1 and N1 Effects to Illusory Figures in the Notch Mode of Presentation

The processing of Kanizsa figures have classically been studied by flashing the full “pacmen” inducers at stimulus onset. A recent study, however, has shown that it is advantageous to present illusory figures in the “notch” mode of presentation, that is by leaving the round inducers on screen at all times and by removing the inward-oriented notches delineating the illusory figure at stimulus onset. Indeed, using the notch mode of presentation, novel P1and N1 effects have been found when comparing visual potentials (VEPs) evoked by an illusory figure and the VEPs to a control figure whose onset corresponds to the removal of outward-oriented notches, which prevents their integration into one delineated form. In Experiment 1, we replicated these findings, the illusory figure was found to evoke a larger P1 and a smaller N1 than its control. In Experiment 2, real grey squares were placed over the notches so that one condition, that with inward-oriented notches, shows a large central grey square and the other condition, that with outward-oriented notches, shows four unconnected smaller grey squares. In response to these “real” figures, no P1 effect was found but a N1 effect comparable to the one obtained with illusory figures was observed. Taken together, these results suggest that the P1 effect observed with illusory figures is likely specific to the processing of the illusory features of the figures. Conversely, the fact that the N1 effect was also obtained with real figures indicates that this effect may be due to more global processes related to depth segmentation or surface/object perception

Contour integration across polarities and spatial gaps: from local contrast filtering to global grouping

International audienceThis article introduces an experimental paradigm to selectively probe the multiple levels of visual processing that influence the formation of object contours, perceptual boundaries, and illusory contours. The experiments test the assumption that, to integrate contour information across space and contrast sign, a spatially short-range filtering process that is sensitive to contrast polarity inputs to a spatially long-range grouping process that pools signals from opposite contrast polarities. The stimuli consisted of thin subthreshold lines, flashed upon gaps between collinear inducers which potentially enable the formation of illusory contours. The subthreshold lines were composed of one or more segments with opposite contrast polarities. The polarity nearest to the inducers was varied to differentially excite the short-range filtering process. The experimental results are consistent with neurophysiological evidence for cortical mechanisms of contour processing and with the Boundary Contour System model, which identifies the short-range filtering process with cortical simple cells, and the long-range grouping process with cortical bipole cells

Still living with the Holocaust in a democracy: History, memory and identity in contemporary Germany

This study investigates the influence of history—more specifically the history of the Holocaust—and the politics of memory on the democracy and national identity of Germany when memory is initially denied, silenced and repressed. The politics of memory are defined as a public act, utterance or site where the memory of the past is evoked, discussed, contested, symbolized, publicized, crystallized, formulated, or contained. Such an act, utterance or site can be among other things, a speech, a scholarly publication, or a memorial. By evaluating the history of the politics of memory since 1945 in general and focusing on three contemporary case studies about the politics of memory in Germany during the 1990s in particular, the nature, functions, effects and political divisions of the politics of Holocaust memory are examined in relation to historical developments, questions of national self-definition, identity and democracy. The case studies are called “The Goldhagen Controversy Revisited,” “The Walser-Bubis Debate,” and “The National Holocaust Memorial in Berlin.” The key argument of this thesis is that in the German case silenced negative memory and a national identity construct that is solely based on negative nationalism had negative consequences for its democracy. It is concluded that after unification there have been increased efforts to be more pragmatic in dealing with the German past. Nonetheless, what is still unshakeable for any German democratic politician is the conviction that the memory of the Holocaust and the political responsibility that this legacy of the past entails remain constitutive elements of the official definition of the German nation, even though the average German does not necessarily want to carry this legacy to the same degree