Evolution Reaction Overpotential Research Articles

Liquid Exfoliation of Icosahedral Quasicrystals

AbstractThe realization of quasicrystals has attracted a considerable attention due to their unusual structures and properties. The concept of quasicrystals in the atomically thin materials is even more appealing due to the in‐plane covalent bonds and weak interlayer interactions. Here, it is demonstrated that 2D quasicrystals can be created/isolated from bulk phases because of long‐range interlayer ordered aperiodic arrangements. An ultrasonication‐assisted exfoliation of polygrained icosahedral Al–Pd–Mn quasicrystals at room temperature shows the formation of a large area of mono‐ and few layers in threefold quasicrystalline plane. The formation of these layers from random grain orientation consistently indicates that the threefold plane is most stable in comparison to the twofold and fivefold planes in icosahedral clusters. The above experimental observations are further supported with help of theoretical simulations. The mono‐ and few‐layered aperiodic planes render plentiful active sites for the catalysis of hydrogen evolution reaction. The threefold 2D quasicrystalline plane exhibits a hydrogen evolution reaction overpotential of ≈100 mV (160 times less than bulk counterpart) and long‐term durability. These systems constitute the first demonstration of quasicrystalline monolayer ordering in a free‐standing thin layer without requiring the support of periodic or aperiodic substrate.

An enhanced electrochemical energy conversion behavior of thermally treated thin film of 1-dimensional CoTe synthesized from aqueous solution at room temperature

This work reports the influence of thermal treatment on electrocatalytic water oxidation/reduction behaviors of one dimensional CoTe nanotube film deposited on FTO substrate from aqueous solution at room temperature. The optimally annealed film at 200 °C demonstrates substantially better electrocatalytic properties, which can be ascribed to the enhanced electrochemical active surface area and electrical conductivity obtained by improving the intergranular connectivity. In addition, the annealed nanotube film demonstrates highly competitive performance to that of many outstanding electrocatalysts for overall splitting of alkaline water to generate hydrogen as green fuel with the oxygen evolution reaction overpotential of 0.37 V (without iR-compensation) for the benchmark current density of 10 mA cm−2.

Water interaction with perfect and fluorine-doped Co3O4 (100) surface

We report the results of theoretical investigations of water adsorption on undoped and fluorine-doped Co3O4 (100) surface by means of the plane-wave periodic density functional theory (DFT) calculations combined with the Hubbard-U approach and statistical thermodynamics. We discuss the effect of fluorine-doping of the Co3O4 (100) surface and calculated oxygen evolution reaction overpotential based on the Gibbs free-energy diagram of undoped and F-doped surfaces.

Design of two-dimensional, ultrathin MoS₂ nanoplates fabricated within one-dimensional carbon nanofibers with thermosensitive morphology: high-performance electrocatalysts for the hydrogen evolution reaction.

Two-dimensional MoS2 nanoplates within carbon nanofibers (CNFs) with monolayer thickness, nanometer-scale dimensions and abundant edges are fabricated. This strategy provides a well-defined pathway for the precise design of MoS2 nanomaterials, offering control over the evolution of MoS2 morphology from nanoparticles to nanoplates as well as from mono- to several-layer structures, over a lateral dimension range of 5 to 70 nm. CNFs play an important role in confining the growth of MoS2 nanoplates, leading to increases in the amount of exposed edge sites while hindering the stacking and aggregation of MoS2 layers, and accelerating electron transfer. The controlled growth of MoS2 nanoplates embedded in CNFs is leveraged to demonstrate structure-dependent catalytic activity in the hydrogen evolution reaction (HER). The results suggest that increases in the number of layers and the lateral dimension result in a decrease in HER activity as a general rule. Single-layer MoS2 nanoplates with abundant edges and a lateral dimension of 7.3 nm demonstrated the lowest hydrogen evolution reaction overpotential of 93 mV (J = 10 mA/cm(2)), the highest current density of 80.3 mA/cm(2) at η = 300 mV and the smallest Tafel slope of 42 mV/decade. The ability of MoS2-CNFs hybrids to act as nonprecious metal catalysts indicates their promise for use in energy-related electrocatalytic applications.

Electrochemical Behavior of Reactively Sputtered Iron‐Doped Nickel Oxide

Iron‐doped nickel oxide films were deposited by reactive sputtering from elemental and alloy targets in a 20% oxygen/argon atmosphere and were characterized for use as oxygen evolution catalysts. The incorporation of iron reduced the overpotential required for oxygen evolution by as much as 300 mV at a current density of 100 mA/cm2 compared to undoped nickel oxide deposited under similar conditions. Tafel slopes were reduced from 95 mV/dec in undoped films to less than 40 mV/dec for films containing 1.6 to 5.6 mole percent (m/o) iron, indicating a change in the rate‐limiting step from the primary discharge of ions to the recombination of oxygen radicals. Resistivity structural and compositional measurements indicate that high oxygen content is necessary to gain the full benefit of the iron dopant. Initial tests in KOH indicate excellent long‐term stability. A film deposited from the FeNi alloy target, which exhibited low oxygen overpotentials and a Tafel slope of 35 mV/dec, had not degraded appreciably following more than 7000 h of operation at an anodic current density of 20 mA/cm2. Taken together, the low oxygen evolution reaction overpotentials, the excellent stability in KOH, and the relative insensitivity to iron content indicate that reactively sputtered iron‐doped nickel oxide is promising as an oxygen catalyst.

The effect of manganese addition on nickel hydroxide electrodes with emphasis on its electrochromic properties

Electrochemical and electrochromic behaviour of Mn + Ni hydroxides composite electrodes prepared by galvanostatic codeposition, were studied. All the composition range form 0 to 100% of Mn was analyzed and they were studied by voltammetry associated with transmittance spectra in 0.1 M KOH electrolytic solution. It was verified that traces of Mn in nickel hydroxide electrodes produce not only the shift of Ni(II)/Ni(III) redox couple towards less positive potentials but also the diminution of the oxygen evolution reaction overpotential. Optical response will be analyzed by means absorption spectra, differentiated absorbance vs. E curves and optical density vs. charge plots.

The Development of an Energy‐Efficient Insoluble Anode for Nickel Electrowinning: I . Single Layer Precious Metal Coatings

Precious metal‐coated titanium insoluble anodes offer several advantages, including increased energy efficiency, over conventional lead electrowinning anodes. PM‐Ti insoluble anodes for electrowinning nickel were developed at the Inco Research and Development Center after establishing a strict economic target of $0.02 of noble metal consumed for each kilogram of nickel electrowon and a minimum life target of six months. Electrodeposited PM coatings on titanium were evaluated in both an accelerated life test at 500 mA/cm2 anode current density in sulfuric acid and a life test which simulated the anolyte conditions of a nickel electrowinning cell. The coatings were then ranked by a figure of merit which was based upon coating life, oxygen evolution reaction overpotential, and cost. A heat‐treated Ru‐4% Ir electrodeposited alloy was found to provide the best combination of these factors and hence was selected for further development.