Overpotential

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

Atomically Dispersed Binary Co-Ni Sites in Nitrogen-Doped Hollow Carbon Nanocubes for Reversible Oxygen Reduction and Evolution.

Abstract: With the inspiration of developing bifunctional electrode materials for reversible oxygen electrocatalysis, one strategy of heteroatom doping is proposed to fabricate dual metal single-atom catalysts. However, the identification and mechanism functions of polynary single-atom structures remain elusive. Atomically dispersed binary Co-Ni sites embedded in N-doped hollow carbon nanocubes (denoted as CoNi-SAs/NC) are synthesized via proposed pyrolysis of dopamine-coated metal-organic frameworks. The atomically isolated bimetallic configuration in CoNi-SAs/NC is identified by combining microscopic and spectroscopic techniques. When employing as oxygen electrocatalysts in alkaline medium, the resultant CoNi-SAs/NC hybrid manifests outstanding catalytic performance for bifunctional oxygen reduction/evolution reactions, boosting the realistic rechargeable zinc-air batteries with high efficiency, low overpotential, and robust reversibility, superior to other counterparts and state-of-the-art precious-metal catalysts. Theoretical computations based on density functional theory demonstrate that the homogenously dispersed single atoms and the synergistic effect of neighboring Co-Ni dual metal center can optimize the adsorption/desorption features and decrease the overall reaction barriers, eventually promoting the reversible oxygen electrocatalysis. This work not only sheds light on the controlled synthesis of atomically isolated advanced materials, but also provides deeper understanding on the structure-performance relationships of nanocatalysts with multiple active sites for various catalytic applications.

Multicomponent electrocatalyst with ultralow Pt loading and high hydrogen evolution activity

Abstract: Platinum is the most effective electrocatalyst for the hydrogen evolution reaction in acidic solutions, but its high cost limits its wide application. Therefore, it is desirable to design catalysts that only require minimal amounts of Pt to function, but that are still highly active. Here we report hydrogen production in acidic water using a multicomponent catalyst with an ultralow Pt loading (1.4 μg per electrode area (cm2)) supported on melamine-derived graphitic tubes (GTs) that encapsulate a FeCo alloy and have Cu deposited on the inside tube walls. With a 1/80th Pt loading of a commercial 20% Pt/C catalyst, in 0.5 M H2SO4 the catalyst achieves a current density of 10 mA cm−2 at an overpotential of 18 mV, and shows a turnover frequency of 7.22 s−1 (96 times higher than that of the Pt/C catalyst) and long-term durability (10,000 cycles). We propose that a synergistic effect between the Pt clusters and single Pt atoms embedded in the GTs enhances the catalytic activity. Although Pt is highly active for electrocatalytic production of H2 from water, its cost limits its wide application. Here, the authors prepare a high-performing catalyst that is supported on graphitic tubes, containing Fe, Co and Cu, and requires only a small amount of Pt.

Improved Charge Transfer at Carbon Nanotube Electrodes

Abstract: The closed topology and tubular structure of carbon nanotubes make them unique among different carbon forms and provide pathways for chemical studies. A number of investigations have been carried out to find applications of nanotubes in catalysis, hydrogen storage, intercalation, etc. Since carbon-electrode-based fuel cells have been experimented with for decades, it is of importance to learn the electrodic performance of these new carbon structures. We report here results of the electrocatalytic reduction of dissolved oxygen (important H2±O2 fuel cell reaction), using microelectrodes constructed from multiwalled nanotubes. In parallel, ab initio calculations were performed for oxygen deposited on the lattice and defect sites of nanotube surfaces to determine the charge transfer during oxygen reduction and compared with similar reactions on planar graphite. The microelectrodes were constructed in the following way (see Fig. 1). Multiwalled nanotubes (10 mg) prepared by the electric arc discharge process and liquid paraffin (4 mL) were intimately mixed, placed in the narrow cylindrical slot of a Perspex holder and then packed by smooth vibration. The assembly was cured at 50 C for 30 min. From the inner side of the Perspex, contact to a copper lead was made through conducting paint. Carbon paste electrodes (based on commercially available graphite powder) were prepared similarly. Carbon nanotube electrodes were prepared earlier by similar techniques to probe bioelectrochemical reactions. The need for oxygen reduction at catalytic surfaces has been recognized in fuel cells, batteries, and many other electrodic applications. Hence, oxygen reduction at nanotube surfaces is of great interest. Electrochemical reduction of dissolved oxygen is carried out in aqueous acidic (H2SO4) and neutral media (1 M KNO3). The solution is first degassed by bubbling nitrogen gas for about 15± 30 min in order to record the background current±voltage curves. Under these conditions, no cyclic voltammetric peak in the potential range 0 to ±0.8 V were observed. The same solutions were then saturated with oxygen by bubbling oxygen gas for 15 min. The cyclic voltammetric curve showed a well-defined peak at Epc = ±0.31 V vs. SCE (saturated calomel electrode) in H2SO4 solution (pH 2) at the carbon nanotube electrodes. At the carbon paste electrodes only an ill-defined peak is seen at Epc = ±0.48 V. In the KNO3 medium (pH 6.2), the reduction of dissolved oxygen is observed at Epc = ±0.51 V at the carbon nanotube electrode. This peak is shifted at the carbon paste electrode by about 30 mV. The shift of the peaks, corresponding to the reaction on the nanotube electrodes, is a strong indication of the electrocatalysis on this electrode (see discussion below). The shift may be considered as an overpotential, which indicates a more facile reaction occurring at the nanotubes compared to other carbons. The electrochemical reduction of oxygen is a function of pH of the medium as proton participation occurs as described by Equation 1.

Electrochemical Activation of CO2 through Atomic Ordering Transformations of AuCu Nanoparticles

Abstract: Precise control of elemental configurations within multimetallic nanoparticles (NPs) could enable access to functional nanomaterials with significant performance benefits. This can be achieved down to the atomic level by the disorder-to-order transformation of individual NPs. Here, by systematically controlling the ordering degree, we show that the atomic ordering transformation, applied to AuCu NPs, activates them to perform as selective electrocatalysts for CO2 reduction. In contrast to the disordered alloy NP, which is catalytically active for hydrogen evolution, ordered AuCu NPs selectively converted CO2 to CO at faradaic efficiency reaching 80%. CO formation could be achieved with a reduction in overpotential of ∼200 mV, and catalytic turnover was enhanced by 3.2-fold. In comparison to those obtained with a pure gold catalyst, mass activities could be improved as well. Atomic-level structural investigations revealed three atomic gold layers over the intermetallic core to be sufficient for enhanced ca...

Nitrogen-doped graphene supported CoSe₂ nanobelt composite catalyst for efficient water oxidation.

Abstract: The slow kinetics of the oxygen evolution reaction (OER) greatly hinders the large-scale production of hydrogen fuel from water splitting. Although many OER electrocatalysts have been developed to negotiate this difficult reaction, substantial progresses in the design of cheap, robust, and efficient catalysts are still required and have been considered a huge challenge. Here, we report a composite material consisting of CoSe2 nanobelts anchored on nitrogen-doped reduced graphene oxides (denoted as NG-CoSe2) as a highly efficient OER electrocatalyst. In 0.1 M KOH, the new NG-CoSe2 catalyst afforded a current density of 10 mA cm–2 at a small overpotential of mere 0.366 V and a small Tafel slope of ∼40 mV/decade, comparing favorably with the state-of-the-art RuO2 catalyst. This NG-CoSe2 catalyst also presents better stability than that of RuO2 under harsh OER cycling conditions. Such good OER performance is comparable to the best literature results and the synergistic effect was found to boost the OER perfor...