line not appear in plot
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Below are my code, why the plot not appear. someone help
% PEM Electrolyzer Activation Overvoltage Plot
% Constants
ioa = 2e-9; % Anode exchange current density (A/cm2)
ioc = 2e-3; % Cathode exchange current density (A/cm2)
T = 297; % Temperature (K)
R = 8.314; % General gas constatnt (J/Kmol)
ctca = 0.5 ; % charge transfer coefficient anode
ctcc = 0.5 ; % charge transfer coefficient cathode
z = 2 ; % stoichiometric coefficient
F = 96485; % Faradays constant
% Operating current density range
i_density = linspace(0, 1.5, 100); % Current density range (A/m^2)
% Calculate activation overvoltage
a = R.*T/ctca.*z.*F;
b = R.*T/ctcc.*z.*F;
eta_activation = log((i_density/ioa).^(a))+(-log((i_density/ioc).^(b)))
% Plot the results
plot(i_density, eta_activation,"b");
2 个评论
Dyuman Joshi
2024-1-28
The plot is empty because all the values are NaN, see the edit above.
amirul
2024-1-29
回答（1 个）
The ‘i_density’ vector begins with 0 and the log of 0 is -Inf.
Starting it instead with a very small value, and re-writing ‘eta_activation’ to use simple log identities produces finite results.
There is some variation in ‘eta_activation’, as demonstrated by the derivative plot (added) —
% PEM Electrolyzer Activation Overvoltage Plot
% Constants
ioa = 2e-9; % Anode exchange current density (A/cm2)
ioc = 2e-3; % Cathode exchange current density (A/cm2)
T = 297; % Temperature (K)
R = 8.314; % General gas constatnt (J/Kmol)
ctca = 0.5 ; % charge transfer coefficient anode
ctcc = 0.5 ; % charge transfer coefficient cathode
z = 2 ; % stoichiometric coefficient
F = 96485; % Faradays constant
% Operating current density range
i_density = linspace(1E-12, 1.5, 100); % Current density range (A/m^2)
% Calculate activation overvoltage
a = R.*T/ctca.*z.*F;
b = R.*T/ctcc.*z.*F;
eta_activation = log((i_density/ioa).^(a))+(-log((i_density/ioc).^(b))) % Original
eta_activation = a*log(i_density/ioa) - b*log(i_density/ioc) % Rewritten
deta_activation_di_density = gradient(eta_activation,i_density) % Derivative
% Plot the results
figure
plot(i_density, eta_activation,"b");
xlabel('i\_density')
ylabel('eta\_activation')
figure
plot(i_density, deta_activation_di_density,"g");
xlabel('i\_density')
ylabel('$\frac{d(eta\_activation)}{d(i\_density)}$', 'Interpreter','latex')
.
4 个评论
@amirul For PEM electrolyzer, the forumula for activation energy is written in a different way.
The constants a and b are calculated incorrectly, see below. As mentioned by @Star Strider, use a small value at starting point,to avoid the Inf values while calculation.
% PEM Electrolyzer Activation Overvoltage Plot
% Constants
ioa = 2e-9; % Anode exchange current density (A/cm2)
ioc = 2e-3; % Cathode exchange current density (A/cm2)
T = 297; % Temperature (K)
R = 8.314; % General gas constatnt (J/Kmol)
ctca = 0.5 ; % charge transfer coefficient anode
ctcc = 0.5 ; % charge transfer coefficient cathode
z = 2 ; % stoichiometric coefficient
F = 96485; % Faradays constant
% Operating current density range
i_density = linspace(0, 1.5, 100); % Current density range (A/m^2)
% Calculate activation overvoltage
a = R.*T/(ctca.*z.*F); % use the parenthesis for denominator acc to formula
b = R.*T/(ctcc.*z.*F);
eta_activation = log((i_density/ioa).^(a))-log((i_density/ioc).^(b))
% Plot the results
plot(i_density, eta_activation,"b");
Star Strider
2024-1-28
@VBBV — Thank you!
I would never have caught the errors in ‘a’ and ‘b’ (denominator factors need to be in parentheses).
amirul
2024-1-29
Star Strider
2024-1-29
Our pleasure!
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2024-1-29
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