Overpotential

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

Nanoporous Graphene Enriched with Fe/Co‐N Active Sites as a Promising Oxygen Reduction Electrocatalyst for Anion Exchange Membrane Fuel Cells

Abstract: Here, a simple but efficient way is demonstrated for the preparation of nanoporous graphene enriched with Fe/Co–nitrogen-doped active sites (Fe/Co-NpGr) as a potential electrocatalyst for the electrochemical oxygen reduction reaction (ORR) applications. Once graphene is converted into porous graphene (pGr) by a controlled oxidative etching process, pGr can be converted into a potential electrocatalyst for ORR by utilizing the created edge sites of pGr for doping nitrogen and subsequently to utilize the doped nitrogens to build Fe/Co coordinated centers (Fe/Co-NpGr). The structural information elucidated using both XPS and TOF-SIMS study indicates the presence of coordination of the M–N (M = Fe and Co)-doped carbon active sites. Creation of this bimetallic coordination assisted by the nitrogen locked at the pore openings is found to be helping the system to substantially reduce the overpotential for ORR. A 30 mV difference in the overpotential (η) with respect to the standard Pt/C catalyst and high retention in half wave potential after 10 000 cycles in ORR can be attained. A single cell of an anion exchange membrane fuel cell (AEMFC) by using Fe/Co-NpGr as the cathode delivers a maximum power density of ≈35 mWcm−2 compared to 60 mWcm−2 displayed by the Pt-based system.

One-step hydrothermal synthesis of monolayer MoS2 quantum dots for highly efficient electrocatalytic hydrogen evolution

Abstract: Designing MoS2 nanocatalysts with ultrasmall size and few layers is an effective strategy to enhance their electrocatalytic activity in the hydrogen evolution reaction (HER). In this work, uniform MoS2 quantum dots (QDs) are synthesized by a novel and facile hydrothermal route. Transmission electron microscopy and atomic force microscopy measurements show that the resulting products possess a monolayer thickness with an average size of about 3.6 nm. Benefiting from the abundance of exposed catalytic edge sites, as well as the excellent intrinsic conductivity of the monolayer structure, the MoS2 QDs showed excellent catalytic activity with a low overpotential of approximately 160 mV and a small Tafel slope of 59 mV dec−1, which made it a promising HER electrocatalyst for practical applications.

High electrochemical activity of the oxide phase in model ceria–Pt and ceria–Ni composite anodes

Abstract: Fuel cells, and in particular solid-oxide fuel cells (SOFCs), enable high-efficiency conversion of chemical fuels into useful electrical energy and, as such, are expected to play a major role in a sustainable-energy future. A key step in the fuel-cell energy-conversion process is the electro-oxidation of the fuel at the anode. There has been increasing evidence in recent years that the presence of CeO_2-based oxides (ceria) in the anodes of SOFCs with oxygen-ion-conducting electrolytes significantly lowers the activation overpotential for hydrogen oxidation. Most of these studies, however, employ porous, composite electrode structures with ill-defined geometry and uncontrolled interfacial properties. Accordingly, the means by which electrocatalysis is enhanced has remained unclear. Here we demonstrate unambiguously, through the use of ceria–metal structures with well-defined geometries and interfaces, that the near-equilibrium H_2 oxidation reaction pathway is dominated by electrocatalysis at the oxide/gas interface with minimal contributions from the oxide/metal/gas triple-phase boundaries, even for structures with reaction-site densities approaching those of commercial SOFCs. This insight points towards ceria nanostructuring as a route to enhanced activity, rather than the traditional paradigm of metal-catalyst nanostructuring.

Stable Cobalt Nanoparticles and Their Monolayer Array as an Efficient Electrocatalyst for Oxygen Evolution Reaction.

Abstract: Monodisperse cobalt (Co) nanoparticles (NPs) were synthesized and stabilized against oxidation via reductive annealing at 600 °C. The stable Co NPs are active for catalyzing the oxygen evolution reaction (OER) in 0.1 M KOH, producing a current density of 10 mA/cm2 at an overpotential of 0.39 V (1.62 V vs RHE, no iR-correction). Their catalysis is superior to the commercial Ir catalyst in both activity and stability. These Co NPs are also assembled into a monolayer array on the working electrode, allowing the detailed study of their intrinsic OER activity. The Co NPs in the monolayer array show 15 times higher turnover frequency (2.13 s–1) and mass activity (1949 A/g) than the NPs deposited on conventional carbon black (0.14 s–1 and 126 A/g, respectively) at an overpotential of 0.4 V. These stable Co NPs are a promising new class of noble-metal-free catalyst for water splitting.