Overpotential

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

Electrochemical performance of annealed cobalt-benzotriazole/CNTs catalysts towards the oxygen reduction reaction.

Abstract: One of the major limitations yet to the global implementation of polymer electrolyte membrane fuel cells (PEMFCs) is the cathode catalyst. The development of efficient platinum-free catalysts is the key issue to solve the problem of slow kinetics of the oxygen reduction reaction (ORR) and high cost. We report a promising catalyst for ORR prepared through the annealing treatment under inert conditions of the cobalt–benzotriazole (Co–BTA) complex supported on carbon nanotubes (CNTs). The N-rich benzotriazole precursor was chosen based on its ability to complex Co(II) ions and generate under annealing highly reactive radicals able to tune the physicochemical properties of CNTs. X-Ray photoelectron spectroscopy (XPS) was used to follow the surface structure changes and highlight the active electrocatalytic sites towards the ORR. To achieve further evaluation of the catalysts in acidic medium, voltamperometry, rotating disk electrode (RDE), rotating ring-disk electrode (RRDE) and half-cell measurements were performed. The resulting catalysts (Co/N/CNTs) all show catalytic activity towards the ORR, the most active one resulting from annealing at 700 °C. The overall electron transfer number for the catalyzed ORR was determined to be ∼3.7 with no change upon the catalyst loading, suggesting that the ORR was dominated by a 4e− transfer process. The results indicate a promising alternative cathode catalyst for ORR in fuel cells, although its performance is still lower (overpotential around 110 mV evaluated by RDE and RRDE) than the reference Pt/C catalyst.

One-step synthesis of zinc–cobalt layered double hydroxide (Zn–Co-LDH) nanosheets for high-efficiency oxygen evolution reaction

Abstract: Two-dimensional (2D) nanomaterials show great potential for electrocatalysis or other applications that require large surface area. In this work, we developed porous zinc–cobalt layered double hydroxide (Zn–Co-LDH) nanosheets by using a one-step microwave-assisted approach, and examine their oxygen evolution reaction (OER) performance. The Zn–Co-LDH nanosheets with a high specific surface area of 116.4 m2 g−1 exhibit good OER activity, expressed as low onset overpotential, small Tafel slope and large exchange current density. At the overpotential of 0.54 V, the current density of Zn–Co-LDH nanosheets is about 15.06 mA cm−2, which is much higher than that of Zn–Co-LDH nanoparticles. The comparable electrocatalytic performance may be attributed to the porous 2D structure generating more active sites and higher electronic conductivity. Furthermore, the obtained Zn–Co-LDH nanosheets show good stability during long time running at 1.55 V vs. RHE. Accordingly, an effective OER catalyst is exploited by using a simple microwave-assisted synthesis. Such an effective method could be extended to large-scale synthesis of uniform and stable 2D LDH nanomaterials.

Hierarchically Porous Co/Co x M y (M = P, N) as an Efficient Mott-Schottky Electrocatalyst for Oxygen Evolution in Rechargeable Zn-Air Batteries

Abstract: Tailoring composition and morphology of electrocatalysts is of great importance in improving their catalytic performance. Herein, a salt-templated strategy is proposed to construct novel multicomponent Co/Cox My (M = P, N) hybrids with outstanding electrocatalytic performance for the oxygen evolution reaction (OER). The obtained Co/Cox My hybrids present porous sheet-like architecture consisting of many hierarchical secondary building-units. The synthetic strategy depends on a facile and effective dissolution-recrystallization-pyrolysis process under NH3 atmosphere of the precursors, which does not involve any surfactant or long-time hydrothermal pretreatment. That is different from the conventional methods for the synthesis of hierarchical nitrides/phosphides. Benefitting from unique composition/structure-dependent merits, the Co/Cox My hybrids as a typical Mott-Schottky electrocatalyst exhibit good OER performance in an alkaline medium compared with their counterparts, as evidenced by a low overpotential of 334 mV at 10 mA cm-2 and a small Tafel slope of 79.2 mV dec-1 , as well as superior long-term stability. More importantly, the Co/Cox My +Pt/C achieves higher voltaic efficiency and several times longer cycle life than conventional RuO2 +Pt/C catalysts in rechargeable Zn-air batteries. It is envisioned that the present work can provide a new avenue for the development of Mott-Schottky electrocatalysts for sustainable energy storage.

Crystal Phase and Architecture Engineering of Lotus-Thalamus-Shaped Pt-Ni Anisotropic Superstructures for Highly Efficient Electrochemical Hydrogen Evolution

Abstract: The rational design and synthesis of anisotropic 3D nanostructures with specific composition, morphology, surface structure, and crystal phase is of significant importance for their diverse applications. Here, the synthesis of well-crystalline lotus-thalamus-shaped Pt-Ni anisotropic superstructures (ASs) via a facile one-pot solvothermal method is reported. The Pt-Ni ASs with Pt-rich surface are composed of one Ni-rich "core" with face-centered cubic (fcc) phase, Ni-rich "arms" with hexagonal close-packed phase protruding from the core, and facet-selectively grown Pt-rich "lotus seeds" with fcc phase on the end surfaces of the "arms." Impressively, these unique Pt-Ni ASs exhibit superior electrocatalytic activity and stability toward the hydrogen evolution reaction under alkaline conditions compared to commercial Pt/C and previously reported electrocatalysts. The obtained overpotential is as low as 27.7 mV at current density of 10 mA cm-2 , and the turnover frequency reaches 18.63 H2 s-1 at the overpotential of 50 mV. This work provides a new strategy for the synthesis of highly anisotropic superstructures with a spatial heterogeneity to boost their promising application in catalytic reactions.

High-valent bimetal Ni3S2/Co3S4 induced by Cu doping for bifunctional electrocatalytic water splitting

Abstract: Rational design of low-cost and efficient electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is imperative for renewable energy conversion. Herein, for the first time, a facile strategy is developed to synthesize M (M = Fe, Cu, Zn, Mo) doped bimetallic sulfide heterostructure Ni3S2/Co3S4 electrocatalysts. The as-prepared bifunctional Cu-Ni3S2/Co3S4 electrode exhibits excellent electrocatalytic activity for HER and OER in 1 M KOH electrolyte, and it requires only an overpotential of 79 mV (150 mV) to deliver 10 mA cm−2 (20 mA cm-2) current density for HER process. Moreover, it shows a considerable low cell voltage of 1.49 V at the current density of 10 mA cm-2 in a two-electrode configuration which is far surpassing most of the reported bifunctional metal sulfides. Meanwhile, besides increasing the specific surface area of the electrocatalyst by optimizing the microstructure, the introduction of Cu cation could also stimulate the formation of high-valent Ni/Co sites, which can be verified by XPS technique. Density function theory calculations demonstrate that the Cu-doping boosts the formation of high valent Co sites and enhances the charge transfer performance of Ni and Co species, thus promotes intrinsic catalytic activity through modulating the d-band center of Co and reducing the adsorption energy of H and O-containing intermediates (H*, OH*, OOH*) on the surface of the catalyst. This work suggests the importance of exploitation of transition metal ion-doping for promoting the electrocatalytic activity of bimetallic sulfides.