The Experts below are selected from a list of 7968 Experts worldwide ranked by ideXlab platform
Jurgen Schumacher - One of the best experts on this subject based on the ideXlab platform.
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calculation of the energy band diagram of a photoelectrochemical water splitting cell
Journal of Physical Chemistry C, 2014Co-Authors: Peter Cendula, Sixto Gimenez, David S Tilley, Juan Bisquert, Matthias Schmid, Jurgen SchumacherAbstract:A physical model is presented for the semiconductor electrode of a photoelectrochemical cell. The model accounts for the potential drop in the Helmholtz Layer and thus enables description of both band edge pinning and unpinning. The model is based on the continuity equations for charge carriers and direct charge transfer from the energy bands to the electrolyte. A quantitative calculation of the position of the energy bands and the variation of the quasi-Fermi levels in the semiconductor with respect to the water reduction and oxidation potentials are presented. Calculated photocurrent–voltage curves are compared with established analytical models and experimental data. Our model calculations are suitable to enhance understanding and improve the properties of semiconductors for photoelectrochemical water splitting.
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calculation of energy band diagram of a photoelectrochemical water splitting cell
arXiv: Computational Physics, 2014Co-Authors: Peter Cendula, S D Tilley, Sixto Gimenez, Juan Bisquert, Matthias Schmid, Michael Graetzel, Jurgen SchumacherAbstract:A physical model is presented for a semiconductor electrode of a photoelectrochemical (PEC) cell, accounting for the potential drop in the Helmholtz Layer. Hence both band edge pinning and unpinning are naturally included in our description. The model is based on the continuity equations for charge carriers and direct charge transfer from the energy bands to the electrolyte. A quantitative calculation of the position of the energy bands and the variation of the quasi-Fermi levels in the semiconductor with respect to the water reduction and oxidation potentials is presented. Calculated current-voltage curves are compared with established analytical models and measurement. Our model calculations are suitable to enhance understanding and improve properties of semiconductors for photoelectrochemical water splitting.
Peter Cendula - One of the best experts on this subject based on the ideXlab platform.
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calculation of the energy band diagram of a photoelectrochemical water splitting cell
Journal of Physical Chemistry C, 2014Co-Authors: Peter Cendula, Sixto Gimenez, David S Tilley, Juan Bisquert, Matthias Schmid, Jurgen SchumacherAbstract:A physical model is presented for the semiconductor electrode of a photoelectrochemical cell. The model accounts for the potential drop in the Helmholtz Layer and thus enables description of both band edge pinning and unpinning. The model is based on the continuity equations for charge carriers and direct charge transfer from the energy bands to the electrolyte. A quantitative calculation of the position of the energy bands and the variation of the quasi-Fermi levels in the semiconductor with respect to the water reduction and oxidation potentials are presented. Calculated photocurrent–voltage curves are compared with established analytical models and experimental data. Our model calculations are suitable to enhance understanding and improve the properties of semiconductors for photoelectrochemical water splitting.
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calculation of energy band diagram of a photoelectrochemical water splitting cell
arXiv: Computational Physics, 2014Co-Authors: Peter Cendula, S D Tilley, Sixto Gimenez, Juan Bisquert, Matthias Schmid, Michael Graetzel, Jurgen SchumacherAbstract:A physical model is presented for a semiconductor electrode of a photoelectrochemical (PEC) cell, accounting for the potential drop in the Helmholtz Layer. Hence both band edge pinning and unpinning are naturally included in our description. The model is based on the continuity equations for charge carriers and direct charge transfer from the energy bands to the electrolyte. A quantitative calculation of the position of the energy bands and the variation of the quasi-Fermi levels in the semiconductor with respect to the water reduction and oxidation potentials is presented. Calculated current-voltage curves are compared with established analytical models and measurement. Our model calculations are suitable to enhance understanding and improve properties of semiconductors for photoelectrochemical water splitting.
Peter Broekmann - One of the best experts on this subject based on the ideXlab platform.
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competitive anion water and cation water interactions at electrified copper electrolyte interfaces probed by in situ x ray diffraction
Journal of Physical Chemistry C, 2012Co-Authors: Hubert Keller, Martino Saracino, H Nguyen, Thi Mien Trung Huynh, Peter BroekmannAbstract:The full 3D structure of a copper/electrolyte interface is studied by means of in situ surface X-ray diffraction (SXRD) methods. Chloride anions chemisorb on Cu(100) in 10 mM HCl at high potentials under formation of a p(1 × 1)-Cl adLayer. This anionic chemisorption Layer serves as a structural template for the lateral ordering of water molecules and hydronium cations in the near-surface liquid electrolyte. Evidence for this interfacial geometry is mainly derived from the intensity distribution of surface-sensitive X-ray diffraction data along the (10L)-adLayer rod. The characteristic oscillating intensity distribution along the (10L) rod is due to a centered biLayer system consisting of the anionic inner Helmholtz Layer (IHL) of chemisorbed chloride and the cationic outer Helmholtz Layer (OHL). The latter is constituted in the present case by hydronium cations that preferentially populate 4-fold hollow sites of the underlying chloride lattice. IHL and OHL are separated by an extra interfacial water Layer...
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surface relaxation phenomena at electrified interfaces revealing adsorbate potential and solvent effects by combined x ray diffraction stm and dft studies
Physical Review B, 2009Co-Authors: Martino Saracino, Peter Broekmann, Knud Gentz, Moritz Becker, Hubert Keller, Florian Janetzko, Thomas Bredow, K WandeltAbstract:Surface relaxation phenomena have been studied in an electrochemical environment using halide modified Cu(100) electrodes as model systems to unravel the impact of the chemical nature of the adsorbed halide, the applied potential, and the presence of solvent species on the surface interLayer spacings. Both, in situ STM and in situ x-ray scattering data point to lateral structures of the adsorbed halides on Cu(100) which are identical for both chloride and bromide. Under saturation conditions both halides form a $p(1\ifmmode\times\else\texttimes\fi{}1)$ adLayer on Cu(100) with reference to a conventional choice of the substrate fcc unit cell. The in situ x-ray scattering data clearly indicate that the copper-halide and the copper-copper interLayer spacings are much more affected by potential changes when bromide is adsorbed on the copper surface and are less affected when chloride is present. This difference in the potential dependence of both halides can be attributed to the larger polarizability of the bromide anion that is almost discharged on the copper surface at the highest applied potentials, while chloride remains largely ionic in the adsorbed state even at the highest applied potential. At the lowest applied potential of ${E}_{\text{work}}=\ensuremath{-}150\text{ }\text{mV}$ [vs reversible hydrogen electrode (RHE)] the Br-Cu and the topmost Cu-Cu Layer distances are expanded by 0.150 and $0.058\text{ }\text{\AA{}}$, respectively, with reference to their bulk analogs CuBr and Cu. These spacings continuously contract by up to 0.075 and $0.038\text{ }\text{\AA{}}$ when the electrode potential is increased to ${E}_{\text{work}}=+50\text{ }\text{mV}$ (RHE). Intriguingly, the second Cu Layer experiences a potential-dependent buckling due to a different second-shell coordination of Cu by bromide while deeper Cu Layers retain the bulk spacing at all potentials. Changes in the halide-copper and the copper-copper interLayer spacings are strongly correlated. An understanding of the in situ x-ray results is achieved by periodic quantum-chemical calculations at density-functional level that allow a modeling of the interfacial structure under consideration of potential and additional solvation effects. The latter originate from interaction of water molecules and counterions in the outer Helmholtz Layer with the specifically adsorbed halides in the inner Helmholtz Layer.
F K Crundwell - One of the best experts on this subject based on the ideXlab platform.
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the mechanism of dissolution of minerals in acidic and alkaline solutions part v surface charge and zeta potential
Hydrometallurgy, 2016Co-Authors: F K CrundwellAbstract:Abstract The theory of dissolution presented in this series of papers was used to model the zeta potential of various representative minerals from the sulphide, oxides and silicates. The calculation of the potential difference across the Helmholtz Layer during the dissolution of these minerals was combined with a simple Gouy–Chapman–Stern model of the electrified interface. The correspondence between the proposed model and experimental data reported in the literature is good, providing confidence in the proposed model and the proposed theory of dissolution. The proposed model is also in accordance with the thermodynamic model of reversible interfaces, such as AgI.
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the mechanism of dissolution of minerals in acidic and alkaline solutions part iii application to oxide hydroxide and sulfide minerals
Hydrometallurgy, 2014Co-Authors: F K CrundwellAbstract:Abstract The reactions of oxide and sulfide minerals with acids are among the most straight-forward of chemical reactions. Despite this, there are still aspects which are not fully understood or explained. The rate of dissolution of these minerals is remarkable, in the sense that their orders of reaction with respect to H + are most often either 0.5 or 1. In addition, the rate of dissolution is strongly dependent on the metal-oxide bond strength. It is proposed that the breaking of the metal–oxygen or metal-sulfur bond under the influence of the interfacial potential difference determines the rate of dissolution. Both metal atoms and oxygen or sulfur atoms at the surface react independently with species in the solution. The rates of these independent processes are coupled by the potential difference across the Helmholtz Layer. The mechanism of dissolution proposed here correctly predicts the observed orders of reaction.
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the anodic dissolution of pyrite fes2 in hydrochloric acid solutions
Hydrometallurgy, 2014Co-Authors: L J Bryson, F K CrundwellAbstract:Abstract Pyrite is an abundant mineral, and its dissolution is important in the formation of acid mine drainage and the extraction of metals. It has also been considered as a candidate material for electrochemical solar cells. We studied the anodic processes on pyrite in hydrochloric acid. The current–voltage curve at steady state has three regions. At potentials below 0.6 V, the current is low, and the Tafel slope is high; between 0.6 and 0.9 V, the current is significant, and the Tafel slope is 0.082 V/decade; at potentials above 0.9 V, the current remains high, but the Tafel slope changes to 0.430 V/decade. From careful measurements of the dissolution of pyrite by chlorine, we show that this third region is due to charge transfer and not ohmic resistance. The shape of the current–voltage curve is unaffected by the type of acid used. The effect of temperature was measured, and the activation energies for the middle and upper region are 46 and 105 kJ/mol, respectively. The steady-state current–voltage curves are not affected by the concentration of HCl, but are affected by the concentration of chloride ions, with an order of reaction of − 0.1, indicating that the rate only slightly dependent on chloride ions. Pretreatment tests and XPS analysis of the surface confirm that the change in Tafel slope is not due to the formation of a surface coating or oxidation product. A comprehensive model of the anodic dissolution of pyrite that describes the current–voltage behavior of pyrite over the entire anodic region is proposed. At low potentials, the behavior of pyrite is typical of an n-type semiconductor with some dissolution. However, as the potential is increased, the Fermi level overlaps with an intrinsic surface state. The rate of dissolution of the pyrite in this region is dependent on the occupancy of the surface state. This accounts for previous reports indicating that pyrite is quasi-metallic. The rate-determining step is the transfer of charge across the space-charge Layer. As the potential is increased to about 0.9 V, the surface state is unoccupied, and the rate-determining step changes to the transfer of ions across the Helmholtz Layer. An expression based on this model fits the experimental data. An important feature of this model is that it also explains two contradictory features of pyrite electrochemistry. On the one hand, n-type and p-type pyrite samples may have similar kinetic parameters, which suggests that the electronic structure of pyrite makes little difference. On the other hand, illuminating the sample with light increases the rate of dissolution, which suggests that the electronic structure is important. The proposed model based on surface states explains these seemingly contradictory observations.
Sixto Gimenez - One of the best experts on this subject based on the ideXlab platform.
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calculation of the energy band diagram of a photoelectrochemical water splitting cell
Journal of Physical Chemistry C, 2014Co-Authors: Peter Cendula, Sixto Gimenez, David S Tilley, Juan Bisquert, Matthias Schmid, Jurgen SchumacherAbstract:A physical model is presented for the semiconductor electrode of a photoelectrochemical cell. The model accounts for the potential drop in the Helmholtz Layer and thus enables description of both band edge pinning and unpinning. The model is based on the continuity equations for charge carriers and direct charge transfer from the energy bands to the electrolyte. A quantitative calculation of the position of the energy bands and the variation of the quasi-Fermi levels in the semiconductor with respect to the water reduction and oxidation potentials are presented. Calculated photocurrent–voltage curves are compared with established analytical models and experimental data. Our model calculations are suitable to enhance understanding and improve the properties of semiconductors for photoelectrochemical water splitting.
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calculation of energy band diagram of a photoelectrochemical water splitting cell
arXiv: Computational Physics, 2014Co-Authors: Peter Cendula, S D Tilley, Sixto Gimenez, Juan Bisquert, Matthias Schmid, Michael Graetzel, Jurgen SchumacherAbstract:A physical model is presented for a semiconductor electrode of a photoelectrochemical (PEC) cell, accounting for the potential drop in the Helmholtz Layer. Hence both band edge pinning and unpinning are naturally included in our description. The model is based on the continuity equations for charge carriers and direct charge transfer from the energy bands to the electrolyte. A quantitative calculation of the position of the energy bands and the variation of the quasi-Fermi levels in the semiconductor with respect to the water reduction and oxidation potentials is presented. Calculated current-voltage curves are compared with established analytical models and measurement. Our model calculations are suitable to enhance understanding and improve properties of semiconductors for photoelectrochemical water splitting.