Overpotential

About: Overpotential is a research topic. Over the lifetime, 16474 publications have been published within this topic receiving 616632 citations.

Direct insights into the role of epoxy groups on cobalt sites for acidic H2O2 production

Abstract: Hydrogen peroxide produced by electrochemical oxygen reduction reaction provides a potentially cost effective and energy efficient alternative to the industrial anthraquinone process. In this study, we demonstrate that by modulating the oxygen functional groups near the atomically dispersed cobalt sites with proper electrochemical/chemical treatments, a highly active and selective oxygen reduction process for hydrogen peroxide production can be obtained in acidic electrolyte, showing a negligible amount of onset overpotential and nearly 100% selectivity within a wide range of applied potentials. Combined spectroscopic results reveal that the exceptionally enhanced performance of hydrogen peroxide generation originates from the presence of epoxy groups near the Co–N4 centers, which has resulted in the modification of the electronic structure of the cobalt atoms. Computational modeling demonstrates these electronically modified cobalt atoms will enhance the hydrogen peroxide productivity during oxygen reduction reaction in acid, providing insights into the design of electroactive materials for effective peroxide production. The production of hydrogen peroxide by electrochemical oxygen reduction is an attractive alternative to the industrial process, but catalysts should be optimized. Here, the authors enhance hydrogen peroxide production in acidic media with epoxy groups near cobalt centers on carbon nanotubes.

Highly Porous Materials as Tunable Electrocatalysts for the Hydrogen and Oxygen Evolution Reaction

Abstract: The facile preparation of highly porous, manganese doped, sponge-like nickel materials by salt melt synthesis embedded into nitrogen doped carbon for electrocatalytic applications is shown. The incorporation of manganese into the porous structure enhances the nickel catalyst's activity for the hydrogen evolution reaction in alkaline solution. The best catalyst demonstrates low onset overpotential (0.15 V) for the hydrogen evolution reaction along with high current densities at higher potentials. In addition, the possibility to alter the electrocatalytic properties of the materials from the hydrogen to oxygen evolution reaction by simple surface oxidation is shown. The surface area increases up to 1200 m2g−1 after mild oxidation accompanied by the formation of nickel oxide on the surface. A detailed analysis shows a synergetic effect of the oxide formation and the material's surface area on the catalytic performance in the oxygen evolution reaction. In addition, the synthesis of cobalt doped sponge-like nickel materials is also delineated, demonstrating the generality of the synthesis. The facile salt melt synthesis of such highly porous metal based materials opens new possibilities for the fabrication of diverse electrode nanostructures for electrochemical applications.

Active Edge Sites Engineering in Nickel Cobalt Selenide Solid Solutions for Highly Efficient Hydrogen Evolution

Abstract: An effective multifaceted strategy is demonstrated to increase active edge site concentration in Ni0.33Co0.67Se2 solid solutions prepared by in situ selenization process of nickel cobalt precursor. The simultaneous control of surface, phase, and morphology result in as-prepared ternary solid solution with extremely high electrochemically active surface area (Cdl = 197 mF cm−2), suggesting significant exposure of active sites in this ternary compound. Coupled with metallic-like electrical conductivity and lower free energy for atomic hydrogen adsorption in Ni0.33Co0.67Se2, identified by temperature-dependent conductivities and density functional theory calculations, the authors have achieved unprecedented fast hydrogen evolution kinetics, approaching that of Pt. Specifically, the Ni0.33Co0.67Se2 solid solutions show a low overpotential of 65 mV at −10 mV cm−2, with onset potential of mere 18 mV, an impressive small Tafel slope of 35 mV dec−1, and a large exchange current density of 184 µA cm−2 in acidic electrolyte. Further, it is shown that the as-prepared Ni0.33Co0.67Se2 solid solution not only works very well in acidic electrolyte but also delivers exceptional hydrogen evolution reaction (HER) performance in alkaline media. The outstanding HER performance makes this solid solution a promising candidate for mass hydrogen production.

Iridium Oxide/Platinum Electrocatalysts for Unitized Regenerative Polymer Electrolyte Fuel Cells

Abstract: To improve the water electrolysis performance of unitized regenerative fuel cells, ultrafine powder was synthesized from colloidal precursors, and an active electrode for oxygen evolution and reduction was prepared by mixing the powder and Pt black. Analysis showed that the surface area of the synthesized was higher than that of high‐surface‐area Pt black. During fuel cell operation, increased the overpotential slightly; however during water electrolysis, the mixed electrocatalyst had a considerably higher activity for oxygen evolution. The addition of only a small amount of to the oxygen electrode was sufficient for the unitized regenerative fuel cell. © 2000 The Electrochemical Society. All rights reserved.