1,721,041 research outputs found
Self-promotion mechanism for CO electrooxidation on gold
No full textCO electrooxidation on Au(111), Au(100) and Au(110) electrodes in 0.1 M HClO4 and 0.1 M NaOH solutions has been studied by means of voltammetric measurements with hanging meniscus rotating bead-type electrodes . It is found that the reaction order in CO concentration is close to unity at potentials close to the onset of CO oxidation , and then it becomes higher than unity at higher potentials for all studied surfaces except for Au(111) in 0.1 M HClO4. This behavior indicates that CO oxidation on gold takes place through a self-promotion mechanism, in which the presence of CO on the gold surface enhances the adsorption of its own oxidant. Specifically, this mechanism offers a plausible explanation for the higher catalytic activity in alkaline solutions, since CO adsorption is stronger under these conditions, and thus it can lead to a higher enhancement of the adsorption of the oxidant specie
Promotion of the oxidation of carbon monoxide at stepped platinum single-crystal electrodes in alkaline media by lithium and beryllium cations
No full textThe role of alkali cations (Li+, Na+, K+, Cs+, and Be2+) on the blank voltammetric response and the oxidative stripping of carbon monoxide from stepped Pt single-crystal electrodes in alkaline media has been investigated by cyclic voltammetry. A strong influence of the nature of the cation on both the blank voltammetric profile and the CO oxidation is observed and related to the influence of the cation on the specific adsorption of OH on the platinum surface. Especially Li+ and Be2+ cations markedly affect the adsorption of OH and thereby have a significant promoting effect on COads oxidation. The voltammetric experiments suggest that, on Pt(111), the influence of Li+ (and Be2+) is primarily through a weakening of the repulsive interactions between the OH in the OH adlayer, whereas in the presence of steps also, the onset of OH adsorption is at a lower potential, both on steps and on terraces
Theory of the transition from sequential to concerted electrochemical proton-electron transfer
Full text linkA theory for the calculation of potential energy surfaces of electrochemical proton-coupled electron transfer is considered and parameterized on the basis of thermodynamic relations. The paper discusses the qualitatively different potential energy surfaces predicted by the theory, and their relation to the existence of sequential and concerted proton-electron transfer pathways. The concomitant activation energies for sequential and concerted PET are calculated. The applied overpotential may change the qualitative shape of the PES and therefore the mechanism of the proton-coupled electron transfer reaction
Analysis of electrocatalytic reaction schemes : distinction between rate-determining and potential-determining steps
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Combined effects of electrode morphology and electrolyte composition on single H 2 gas bubble detachment during hydrogen evolution reaction
Full text linkDepending on the direction of the Marangoni effects, gas bubble locations and consequently the force balance determining gas bubble detachment can vary significantly.During the hydrogen evolution reaction, H 2 gas bubbles form on the electrode surface, significantly affecting electrochemical processes, particularly at high current densities. While promoting bubble detachment has been shown to enhance the current density, the mechanisms governing gas bubble detachment at the electrochemical interface remain poorly understood. In this study, we investigated the interplay between electrode surface morphology and electrolyte composition on single H 2 gas bubble detachment during hydrogen evolution reaction (HER). Using well-defined Pt microelectrodes as model systems, we systematically modify and enhance their surface roughness through mechanical polishing to investigate these effects in detail. By modulating the Marangoni effect through variations in electrolyte composition and applied potential, we identified two distinct detachment behaviours. When the Marangoni force acts towards the electrodes, H 2 gas bubbles are positioned closer to the electrode surface and exhibit roughness-dependent detachment, with smaller bubbles detaching earlier on rougher surfaces. Conversely, when the Marangoni force is directed away from the electrode, H 2 gas bubbles are located farther from the electrode surface and show roughness-independent detachment sizes. These findings highlight the importance of considering both electrode and electrolyte effects to optimize gas bubble detachment during electrochemical reactions.Depending on the direction of the Marangoni effects, gas bubble locations and consequently the force balance determining gas bubble detachment can vary significantly.During the hydrogen evolution reaction, H 2 gas bubbles form on the electrode surface, significantly affecting electrochemical processes, particularly at high current densities. While promoting bubble detachment has been shown to enhance the current density, the mechanisms governing gas bubble detachment at the electrochemical interface remain poorly understood. In this study, we investigated the interplay between electrode surface morphology and electrolyte composition on single H 2 gas bubble detachment during hydrogen evolution reaction (HER). Using well-defined Pt microelectrodes as model systems, we systematically modify and enhance their surface roughness through mechanical polishing to investigate these effects in detail. By modulating the Marangoni effect through variations in electrolyte composition and applied potential, we identified two distinct detachment behaviours. When the Marangoni force acts towards the electrodes, H 2 gas bubbles are positioned closer to the electrode surface and exhibit roughness-dependent detachment, with smaller bubbles detaching earlier on rougher surfaces. Conversely, when the Marangoni force is directed away from the electrode, H 2 gas bubbles are located farther from the electrode surface and show roughness-independent detachment sizes. These findings highlight the importance of considering both electrode and electrolyte effects to optimize gas bubble detachment during electrochemical reactions.National Research Foundation of Korea https://doi.org/10.13039/501100003725European Research Council https://doi.org/10.13039/50110000078
Performance Enhancement of Electrocatalytic Hydrogen Evolution through Coalescence-Induced Bubble Dynamics
Full text linkThe evolution of electrogenerated gas bubbles during water electrolysis can significantly hamper the overall process efficiency. Promoting the departure of electrochemically generated bubbles during (water) electrolysis is therefore beneficial. For a single bubble, a departure from the electrode surface occurs when buoyancy wins over the downward-acting forces (e.g., contact, Marangoni, and electric forces). In this work, the dynamics of a pair of H2 bubbles produced during the hydrogen evolution reaction in 0.5 M H2SO4 using a dual platinum microelectrode system is systematically studied by varying the electrode distance and the cathodic potential. By combining high-speed imaging and electrochemical analysis, we demonstrate the importance of bubble-bubble interactions in the departure process. We show that bubble coalescence may lead to substantially earlier bubble departure as compared to buoyancy effects alone, resulting in considerably higher reaction rates at a constant potential. However, due to continued mass input and conservation of momentum, repeated coalescence events with bubbles close to the electrode may drive departed bubbles back to the surface beyond a critical current, which increases with the electrode spacing. The latter leads to the resumption of bubble growth near the electrode surface, followed by buoyancy-driven departure. While less favorable at small electrode spacing, this configuration proves to be very beneficial at larger separations, increasing the mean current up to 2.4 times compared to a single electrode under the conditions explored in this study.</p
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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