Naomi Levy

Application of a quartz-crystal microbalance to measure ionic fluxes in microporous carbons for energy storage

Fast ionic transport in microporous activated-carbon electrodes is a prerequisite for the effective energy storage in electrochemical supercapacitors. However, the quartz-crystal microbalance (QCM), a direct tool to measure ionic fluxes in electrochemical systems, has not yet been used for studying transport phenomena in activated carbons (except for an early report on carbon nanotubes). Conventional electroanalytical and suitable surface and structure-analysis techniques provide limited prognostic information on this matter. It has been demonstrated herein that the QCM response of typical microporous activated carbons can serve as a gravimetric probe of the concentration and compositional changes in their pore volume. This allowed direct monitoring of the ionic fluxes, which depended strongly on the electrodes point of zero change, pore width, ion size and cycling conditions (polarization amplitude, charge/discharge depth and so on). The information on the nature of ionic fluxes into activated carbons is critical for promoting improvements in the performance of electrochemical supercapacitors, membrane technologies and (electro/bio)chemical sensors.

Electrochemical quartz crystal microbalance (EQCM) studies of ions and solvents insertion into highly porous activated carbons.

Electrochemical quartz crystal microbalance (EQCM) technique provides a direct assessment to the behavior of electroadsorbed ions and solvent molecules confined in micropores of activated carbon electrodes in contact with practically important aprotic electrolyte solutions. The estimated value of the solvation number equal to 3 is evident for a partial desolvation of Li(+) cations when adsorbed in carbon micropores.

Metallocorroles as Nonprecious‐Metal Catalysts for Oxygen Reduction

The future of affordable fuel cells strongly relies on the design of earth-abundant (non-platinum) catalysts for the electrochemical oxygen reduction reaction (ORR). However, the bottleneck in the overall process occurs therein. We have examined herein trivalent Mn, Fe, Co, Ni, and Cu complexes of β-pyrrole-brominated corrole as ORR catalysts. The adsorption of these complexes on a high-surface-area carbon powder (BP2000) created a unique composite material, used for electrochemical measurements in acidic aqueous solutions. These experiments disclosed a clear dependence of the catalytic activity on the metal center of the complexes, in the order of Co>Fe>Ni>Mn>Cu. The best catalytic performance was obtained for the Co(III) corrole, whose onset potential was as positive as 0.81 V versus the reversible hydrogen electrode (RHE). Insight into the properties of these systems was gained by spectroscopic and computational characterization of the reduced and oxidized forms of the metallocorroles.

Metallocorroles as Non-Precious Metal Electrocatalysts for Highly Efficient Oxygen Reduction in Alkaline Media

A series of non‐precious metal complexes, composed of five first‐row transition‐metal complexes with β‐pyrrole‐brominated 5,10,15‐tris(pentafluorophenyl)corroles [M(tpfcBr8), M=Mn, Fe, Co, Ni, and Cu], was investigated as catalysts for oxygen reduction in an alkaline solution (0.1 m KOH). The corroles were adsorbed on a high surface area carbon powder (BP2000) prior to electrochemical measurements to create a unique composite material. The comparison between the different metal complexes revealed a high oxygen reduction reaction (ORR) catalytic performance in the case of the Fe‐ and Co‐corroles. These complexes reduce oxygen at very low overpotentials (with E1/2=0.79 V and 0.77 V vs. RHE, respectively), which is better than other well‐defined molecular catalysts and comparable to that of Pt on carbon (XC‐72). The mechanism by which the most active complexes catalyze the ORR in alkaline solutions was also studied, disclosing that the dominant reaction path is a four‐electron reduction of molecular oxygen to hydroxide.

Review on Engineering and Characterization of Activated Carbon Electrodes for Electrochemical Double Layer Capacitors and Separation Processes

Carbonaceous materials are highly important electrode materials due to their wide electrochemical window, inertness with a wide spectrum of electroactive materials, and the possibility to develop highly porous but yet conductive activated carbons. Carbon cloth electrodes could be prepared from simple polymeric materials such as cotton cloth (poly-cellulose) and then could be activated by mild oxidation processes (e.g., using CO2 at elevated temperatures). Monolithic, conductive carbon cloth electrodes with specific surface area up to 2000 m2/g could be obtained and their porosity could be adjusted by the activation process and calibrated by adsorption processes from both gas and solution phases. Capacities up to 350 F/g could be obtained with activated carbon electrodes in acidic aqueous solutions, which makes these systems very promising for super-capacitor devices. Highly interesting are the correlations between electro-adsorption processes and the electrical properties of activated carbon electrodes, as described herein. This review provides useful guidelines for the engineering of porous carbon electrodes and their characterization by electrochemical, spectral, and physical methods.

Prosaccade and Antisaccade Paradigms in Persons with Alzheimer’s Disease: A Meta-Analytic Review

Persons with Mild Cognitive Impairment (MCI) are at high Alzheimer’s Disease (AD) risk but the development of sensitive measures to assess subtle cognitive decline in this population poses a major challenge for clinicians and researchers. Eye movement monitoring is a non-invasive, sensitive way to assess subtle cognitive processes in clinical populations. We conducted a critical review and a meta-analysis of the literature on pro and antisaccade paradigm in AD/MCI. The meta-analysis included 20 studies, all of which used the prosaccade paradigm and 13 of which studied the antisaccade paradigm as well. Our meta-analysis showed that AD but not MCI patients showed longer prosaccade latencies when compared to controls. While antisaccade latencies did not differentiate between patients from controls, antisaccade error rate were significantly increased among patients in comparison to controls in over 87% of the studies. These findings highlight antisaccade error rate as a reliable tool to distinguish inhibition abilities between AD/MCI and healthy older persons.

Bioinspired Electrocatalysis of Oxygen Reduction Reaction in Fuel Cells Using Molecular Catalysts

One of the most important chemical reactions for renewable energy technologies such as fuel cells and metal-air batteries today is oxygen reduction. Due to the relatively sluggish reaction kinetics, catalysts are necessary to generate high power output. The most common catalyst for this reaction is platinum, but its scarcity and derived high price have raised the search for abundant nonprecious metal catalysts. Inspired from enzymatic processes which are known to catalyze oxygen reduction reaction efficiently, employing transition metal complexes as their catalytic centers, many are working on the development of bioinspired and biomimetic catalysts of this class. This research news article gives a glimpse of the recent progress on the development of bioinspired molecular catalyst for oxygen reduction, highlighting the importance of the molecular structure of the catalysts, from advancements in porphyrins and phthalocyanines to the most recent work on corroles, and 3D networks such as metal-organic frameworks and polymeric networks, all with nonpyrolyzed, well-defined molecular catalysts for oxygen reduction reaction.