【课件】电极反应动力学燃料电池ppt
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• Kinetics describe the evolution of mass flow throughout the
system, including both the approach to equilibrium and the dynamic maintenance of that state.
• Where α, the transfer coefficient
STANDARD RATE CONSTANT
• It simply is a measure of the kinetic facility of a redox couple.
• A system with a large k0 will achieve equilibrium on a short time scale, but a system with small k0 will be
• we always saw that current is often limited wholly or partially by the rate at which the electroreactants are transported to the electrode surface.
• This kind of limitation does not concern a theory of interfacial kinetics. More to the point is the case of low current and efficient stirring, in which mass transport is not a factor determining the current. Instead, it is controlled by interfacial dynamics.
sluggish. • The largest measured standard rate constants are in
the range of 1 to 10 cm/s, and are associated with particularly simple electron-transfer processes.
2011 SPRING FUEL CELL AND ELECTROCHEMISTRY
Lecture 9 Kinetics of
electrode reactions
DYNAMIC EQUILIBRIUM
DYNAMIC EQUILIBRIUM
• The kinetic theory therefore predicts a constant concentration ratio at equilibrium, just as thermodynamics does;
THE TRANSFER COEFFICIENT
• a should generally be a potential-dependent factor; • In a typical chemical system, the free energies of activation are in the
– Molecular rearrangement upon electron transfer or multistep process can be very sluggish
THE TRANSFER COEFFICIEቤተ መጻሕፍቲ ባይዱT
In most systems a turns out to lie between 0.3 and 0.7, and it can usually be approximated by 0.5 in the absence of actual measurements.
range of a few electron volts, but the full range of measurable kinetics usually corresponds to a change in activation energy of only 50-200 meV, or a few percent of the total.
• Thermodynamics describe only equilibrium.
• Exchange velocity: equilibrium features nonzero rates of
conversion of A to В (and vice versa), but those rates are equal. v0
THE ARRHENIUS EQUATION AND POTENTIAL ENERGY SURFACES
A is the pre-exponential factor k is the reaction rate coefficient EA activation energy
TRANSITION STATE THEORY
EXCHANGE CURRENT
At zero current
At equilibrium, the bulk concentrations of О and R are found also at the surface
TAFEL EQUATION
BUTLERVOLMER MODEL OF ELECTROD
E KINETICS
Suppose the electrode potential
is equal to E°.
The cathodic and anodic activation energies are
• we focus on the special condition in which the entire system—A, B, and all other configurations—is at thermal equilibrium
ESSENTIALS OF ELECTRODE REACTIONS
system, including both the approach to equilibrium and the dynamic maintenance of that state.
• Where α, the transfer coefficient
STANDARD RATE CONSTANT
• It simply is a measure of the kinetic facility of a redox couple.
• A system with a large k0 will achieve equilibrium on a short time scale, but a system with small k0 will be
• we always saw that current is often limited wholly or partially by the rate at which the electroreactants are transported to the electrode surface.
• This kind of limitation does not concern a theory of interfacial kinetics. More to the point is the case of low current and efficient stirring, in which mass transport is not a factor determining the current. Instead, it is controlled by interfacial dynamics.
sluggish. • The largest measured standard rate constants are in
the range of 1 to 10 cm/s, and are associated with particularly simple electron-transfer processes.
2011 SPRING FUEL CELL AND ELECTROCHEMISTRY
Lecture 9 Kinetics of
electrode reactions
DYNAMIC EQUILIBRIUM
DYNAMIC EQUILIBRIUM
• The kinetic theory therefore predicts a constant concentration ratio at equilibrium, just as thermodynamics does;
THE TRANSFER COEFFICIENT
• a should generally be a potential-dependent factor; • In a typical chemical system, the free energies of activation are in the
– Molecular rearrangement upon electron transfer or multistep process can be very sluggish
THE TRANSFER COEFFICIEቤተ መጻሕፍቲ ባይዱT
In most systems a turns out to lie between 0.3 and 0.7, and it can usually be approximated by 0.5 in the absence of actual measurements.
range of a few electron volts, but the full range of measurable kinetics usually corresponds to a change in activation energy of only 50-200 meV, or a few percent of the total.
• Thermodynamics describe only equilibrium.
• Exchange velocity: equilibrium features nonzero rates of
conversion of A to В (and vice versa), but those rates are equal. v0
THE ARRHENIUS EQUATION AND POTENTIAL ENERGY SURFACES
A is the pre-exponential factor k is the reaction rate coefficient EA activation energy
TRANSITION STATE THEORY
EXCHANGE CURRENT
At zero current
At equilibrium, the bulk concentrations of О and R are found also at the surface
TAFEL EQUATION
BUTLERVOLMER MODEL OF ELECTROD
E KINETICS
Suppose the electrode potential
is equal to E°.
The cathodic and anodic activation energies are
• we focus on the special condition in which the entire system—A, B, and all other configurations—is at thermal equilibrium
ESSENTIALS OF ELECTRODE REACTIONS