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| how much do transport processes contribute to electrochemical kinetics measurements? |
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Definition
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| transport processes are based on __ |
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Definition
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| hydrodynamics is described with what type of mathematics? |
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Definition
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in eqn 7.1, Ji = -Di*grad(ci) - [zi*F/(R*T)]Di*ci*grad(phi) + ci*v
the first term represents __ |
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Definition
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Term
in eqn 7.1, Ji = -Di*grad(ci) - [zi*F/(R*T)]Di*ci*grad(phi) + ci*v
the second term represents __ |
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Definition
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Term
in eqn 7.1, Ji = -Di*grad(ci) - [zi*F/(R*T)]Di*ci*grad(phi) + ci*v
the third term represents __ |
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Definition
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| define potentiostatic regime |
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Definition
| current-time dependence at constant potential |
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| current measurements in the potentiostatic regime can be used to find what 3 things? |
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Definition
diffusion layer thickness
time dependence of diffusion layer thickness
diffusion coeff. of electrochemically active species |
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| define galvanostatic regime |
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Definition
| current-time dependence at constant current |
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| two key equations for transport processes in electrochem. systems are the __ and __ |
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Definition
flux vector eqn
molar conc. vs time eqn |
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| in order to set up a constant potential so that current density vs. time can be measured, what is needed? |
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Definition
| a 3-electrode system and a potentiostat |
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| under a galvanostatic regime and when the charge-transfer reaction is fast, the conc. gradient at the electrode surface is __ |
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Definition
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Definition
| time to achieve 0 concentration at the electrode surface |
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| list 2 ways that galvanostatic measurements can be used |
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Definition
1. to define the diffusion coeff. if bulk concentration is known
2. as an analytical tool to measure concentration of the electrochemically active species if the diffusion coeff. is known |
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| galvanostatic measurements can be used to define the diffusion coeff. if... |
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Definition
| bulk concentration is known |
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| galvanostatic measurements can be used as an analytical tool to measure concentration of the electrochemically active species if... |
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Definition
| the diffusion coeff. is known |
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| name 2 ways electrochemical processes can be influenced |
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Definition
by mass transport due to diffusion
by convection |
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in eqn 7.7, (∂ci/∂t) = -Di*Lap^2*ci - v*grad(ci)
the first term represents __ |
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Definition
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Term
in eqn 7.7, (∂ci/∂t) = -Di*Lap^2*ci - v*grad(ci)
the second term represents __ |
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Definition
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Term
for eqn 7.7, (∂ci/∂t) = -Di*Lap^2*ci - v*grad(ci)
it is assumed that when convection in the electrochemical cell is changed, the Nernst diffusion layer is changed or unchanged? |
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Definition
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| cell current depends on hydrodynamics because... |
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Definition
| when convection in the electrochemical cell is changed, the Nernst diffusion layer is also changed |
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| as the intensity of mixing increases, the length of the diffusion layer |
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Definition
decreases
(more intensive mixing = smaller diffusion layer) |
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| Prandtl layer thickness pertains to velocity of solution or to concentration of the electrochemically active species? |
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Definition
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Term
| Nernst diffusion layer thickness pertains to velocity of solution or to concentration of the electrochemically active species? |
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Definition
| concentration of the electrochemically active species |
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Term
| at the distance below the Prandtl layer thickness, what happens to velocity of the solution? |
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Definition
| velocity begins to drop, reaching zero at the electrode surface |
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Term
| at the distance below the Nernst diffusion layer thickness, what happens to concentration of the electrochemically active species? |
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Definition
| concentration begins to drop, reaching zero at the electrode surface |
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Term
| which typically represents a greater distance from the electrode surface, Prandtl layer thickness or Nernst diffusion layer thickness? |
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Definition
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| which typically drops faster when approaching the electrode surface, velocity of the solution or the concentration of the electrochemically active species? |
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Definition
| concentration of the electrochemically active species |
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Term
| when solution current is parallel to the electrode surface and perpendicular to the diffusion direction... |
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Definition
1. Nernst diffusion layer thickness is changing with the length of the electrode
2. the electrode is not equally accessible in the direction of the solution flow |
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Term
| for most systems, if there is mixing of the solution, the Nerst diffusion layer thickness is __ |
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Definition
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| one of the systems where the Nerst diffusion layer thickness is precisely defined is __ |
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Definition
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Term
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Definition
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Term
| what is the main feature of the RDE? |
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Definition
| it is equally accessible at all points on the electrode surface |
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Term
| for the RDE, Nernst diffusion layer thickness depends on what 3 things? |
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Definition
1. diffusion coeff. of the electrochemically active species
2. viscosity and density of the solution
3. rotation rate of the RDE |
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| for the RDE, the limiting current density can be calculated if... |
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Definition
| the bulk concentration of the electrochemically active species is known |
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Term
| for the RDE, as angular velocity (and hence the rotation rate) of the electrode increases, limiting current density __ |
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Definition
| increases
(high ang. velocity = high jlim) |
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Term
| for the RDE, if you plot limiting current vs. the square root of angular velocity, the shape of the line is __ |
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Definition
| a straight line that goes through the origin |
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Term
| for the RDE, calculating the limiting current density at infinite angular velocity is possible or impossible? |
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Definition
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| for the RDE, when angular velocity is infinite, the Nernst diffusion layer thickness equals __ |
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Definition
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Term
| at high overpotentials, the limiting current... |
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Definition
| is entirely determined by transport processes and is therefore independent of potential |
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Term
| what kind of cell should be used with the RDE? |
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Definition
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Term
| to get high quality data, the RDE should be __ |
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Definition
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Term
| to study the electrochemical kinetics of a redox reaction, out of what material should the RDE ideally be made? |
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Definition
platinum
(other materials *can* be used if clean and polished, but Pt is best) |
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Term
| for the RDE, the current density at infinite angular velocity can be used with what equation to calculate exchange current density and symmetry coefficients for the RDE electrochemical reaction? |
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Definition
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