plot not appear even y value is constant

hello pliss help this also. the value not appear in plot even the y-axis value is constant number

% 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

G = 237200; % Gibbs energy

n = 2; % Number of electron

Re = 0.035; % electronic resistance (Ωm)

lambda = 17; % degree of membrane humidification

% Operating current density range

i_density = linspace(0, 1.5, 100); % Current density range (A/m^2)

% Calculate reversible overvoltage

eta_reversible = G/n.*F;

% Plot the results

plot(i_density, eta_reversible,"r");