The dependence of the photocurrent at the metal-electrolyte interface on electrode potential

1975 ◽  
Vol 28 (2) ◽  
pp. 253 ◽  
Author(s):  
DB Matthews ◽  
SUM Khan
Keyword(s):  
Electron Transfer ◽  
Charge Transfer ◽  
Potential Energy ◽  
Physical Interpretation ◽  
Linear Dependence ◽  
Energy Barrier ◽  
Electrode Potential ◽  
Potential Energy Barrier ◽  
Electrolyte Interface ◽  
Solvent Molecules

The Gurney theory of charge transfer at the metal-electrolyte interface is extended to the case of photoemission. It is found that the simple Gurney model is not sufficient to explain the results observed by a number of independent workers. In order to explain the observed linear dependence of the 0.4 power of the photocurrent on electrode potential it is found necessary to allow explicitly for the existence of a layer of solvent molecules at the metal surface. This layer of molecules con- stitutes a potential energy barrier to electron transfer with a width of about 0.28 nm and a height (with respect to the Fermi level of the metal) of about 560 kJ mol-1 for water. The model is geometrically quite similar to that used in the very successful Brodsky model but differs in physical interpretation of the surface potential energy barrier.

The dependence of the rate of electrochemical charge transfer on the electric field at the metal-electrolyte interface

1972 ◽  
Vol 25 (2) ◽  
pp. 231 ◽  
Author(s):  
DB Matthews
Keyword(s):  
Electron Transfer ◽  
Charge Transfer ◽  
Potential Energy ◽  
Electric Field ◽  
Electric Fields ◽  
Potential Energy Curves ◽  
Energy Curve ◽  
Electrolyte Interface ◽  
Activated State ◽  
Wide Range

Electric fields at the metal-electrolyte interface are very high (of the order of 107 V/cm) and one intuitively expects that these fields should have a profound influence on the movement of charged species such as ions and electrons at the interface. Qualitatively, such field effects manifest themselves as deviations from linearity of Tafel plots or as a dependence of the symmetry factor on electrode potential. It is shown that Gurney's potential energy curve representation of charge transfer reactions yields only small changes in β over a wide range of potential, with the anharmonic (Morse) curves showing smaller changes than the harmonic (parabolic) curves. Superposition of the double layer electric field on these potential energy curves increases the curvature of the Tafel plots, but the effect is still not very large, being within the limits of uncertainty in determining the correct form of the potential energy curves. The effect of electric field on electron transfer is considered both from the viewpoint of change in electron transfer distance arising from a dependence of coordinates of the activated state on potential and from the viewpoint of a direct effect on the electron transfer barrier (analogous to field electron emission). The field emission effects are found to be even less than the effects of the field on the proton transfer potential energy barrier.

Hybrid-Bistable Vibration Energy Harvester With Adaptive Potential Well

2018 ◽  
Author(s):  
Jinki Kim ◽  
Patrick Dorin ◽  
K. W. Wang
Keyword(s):  
Energy Harvesting ◽  
Potential Energy ◽  
Cantilever Beam ◽  
Potential Barrier ◽  
Energy Barrier ◽  
Electrical Power ◽  
Vibration Energy ◽  
Frequency Spectra ◽  
Potential Energy Barrier ◽  
Piezoelectric Energy

Many common environmental vibration sources exhibit low and broad frequency spectra. In order to exploit such excitations, energy harvesting architectures utilizing nonlinearity, especially bistability, have been widely studied since the energetic interwell oscillations between their stable equilibria can provide enhanced power harvesting capability over a wider bandwidth compared to the linear counterpart. However, one of the limitations of these nonlinear architectures is that the interwell oscillation regime may not be activated for a low excitation level that is not strong enough to overcome the potential energy barrier, thus resulting in low amplitude intrawell response which provides poor energy harvesting performance. While the strategic integration of bistability and additional dynamic elements has shown potential to improve broadband energy harvesting performance by lowering the potential barrier, there is a clear opportunity to further improve the energy harvesting performance by extracting electrical power from the kinetic energy in the additional element that is induced when the potential barrier is lowered. To explore this opportunity and advance the state of the art, this research develops a novel hybrid bistable vibration energy harvesting system with a passive mechanism that not only adaptively lowers the potential energy barrier level to improve broadband performance but also exploits additional means to capture more usable electrical power. The proposed harvester is comprised of a cantilever beam with repulsive magnets, one attached at the free end and the other attached to a linear spring that is axially aligned with the cantilever (a spring-loaded magnet oscillator). This new approach capitalizes on the adaptive bistable potential that is passively realized by the spring-loaded magnet oscillator, which lowers the double-well potential energy barrier thereby facilitating the interwell oscillations of the cantilever across a broad range of excitation conditions, especially for low excitation amplitudes and frequencies. The interwell oscillation of the cantilever beam enhances not only the piezoelectric energy harvesting from the beam but also the electromagnetic energy harvesting from the spring-loaded magnet oscillator by inducing large amplitude vibrations of the magnet oscillator. Numerical investigations found that the proposed architecture yields significantly enhanced energy harvesting performance compared to the conventional bistable harvester with fixed magnet.

The Absence of a Marcus Inversion Region for Electron Transfer at the Metal-Redox Electrolyte Interface

1994 ◽  
Vol 47 (12) ◽  
pp. 2171 ◽  
Author(s):  
D Matthews
Keyword(s):  
Electron Transfer ◽  
Potential Energy ◽  
Electron Distribution ◽  
Distribution Functions ◽  
Rate Distribution ◽  
Inversion Region ◽  
Redox Electrolyte ◽  
Electrolyte Interface ◽  
Metal Redox ◽  
Nuclear Configuration

The theory of electron transfer at the metal- redox electrolyte interface is described by starting with the work of Gurney and incorporating that of Gerischer and Marcus. This GGM model brings together diverse approaches to the description of electron transfer at electrodes. The electron transfer is described in terms of nuclear configuration potential energy diagrams, electronic configuration potential energy diagrams, electron distribution functions and rate distribution functions. The distinction between microscopic energies and macroscopic (thermodynamic) energies is made and the concept of the Fermi level of the redox electrolyte is clarified. The model of identical parabolas is used for the nuclear configuration diagrams and this is shown to lead to Gaussian electron distribution functions for the redox electrolyte. The rate distribution is obtained from the overlap between occupied and unoccupied states of the metal and redox electrolyte. Integration of the rate distribution gives the rate which is calculated as a function of the electrode potential for various values of the reorganization energy λ. It is shown that the variation of symmetry factor β is small for high λ and that the Tafel plots do not show significant decrease in rate at high overpotentials in the anomalous or inversion region. The Tafel plots for charge transfer (mass transfer is assumed to be fast at all potentials) tend to a limiting value with only a small decrease at high overpotential. This contrasts with the prediction based on nuclear configuration potential energy curves and is attributed to the fact that the overlap is between a Gaussian and a Fermi function rather than between two Gaussians, the latter being the case for homogeneous reactions.

scholarly journals The enzyme aromatic amine dehydrogenase induces a substrate conformation crucial for promoting vibration that significantly reduces the effective potential energy barrier to proton transfer

2008 ◽  
Vol 5 (suppl_3) ◽  
pp. 225-232 ◽  
Author(s):  
Linus O Johannissen ◽  
Nigel S Scrutton ◽  
Michael J Sutcliffe
Keyword(s):  
Potential Energy ◽  
Proton Transfer ◽  
Aromatic Amine ◽  
Effective Potential ◽  
Energy Barrier ◽  
Transfer Event ◽  
Effective Potential Energy ◽  
Potential Energy Barrier ◽  
Mechanical Methods ◽  
Amine Dehydrogenase

The role of promoting vibrations in enzymic reactions involving hydrogen tunnelling is contentious. While models incorporating such promoting vibrations have successfully reproduced and explained experimental observations, it has also been argued that such vibrations are not part of the catalytic effect. In this study, we have employed combined quantum mechanical/molecular mechanical methods with molecular dynamics and potential energy surface calculations to investigate how enzyme and substrate motion affects the energy barrier to proton transfer for the rate-limiting H-transfer step in aromatic amine dehydrogenase (AADH) with tryptamine as substrate. In particular, the conformation of the iminoquinone adduct induced by AADH was found to be essential for a promoting vibration identified previously—this lowers significantly the ‘effective’ potential energy barrier, that is the barrier which remains to be surmounted following collective, thermally equilibrated motion attaining a quantum degenerate state of reactants and products. When the substrate adopts a conformation similar to that in the free iminoquinone, this barrier was found to increase markedly. This is consistent with AADH facilitating the H-transfer event by holding the substrate in a conformation that induces a promoting vibration.

The potential energy barrier of the state in KLi

2009 ◽  
Vol 73 (1) ◽  
pp. 117-120 ◽  
Author(s):  
W. Jastrzebski ◽  
P. Kowalczyk ◽  
A. Pashov ◽  
J. Szczepkowski
Keyword(s):  
Potential Energy ◽  
Energy Barrier ◽  
The State ◽  
Potential Energy Barrier
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