Trying to produce non-negative value

%Variables
T = 1073; %Temperature
E_thermo = 1; %Thermodynamic voltage
x_H2_Ia = 0.95;%Hydrogyen inlet mole fraction
x_O2_Id = 0.21; %Oxygen inlet mole fraction
p_c =  1;%cathode pressure
p_a = 1;%anode pressure
D_h2 = 1e-4;%Effective hydrogyen diffusivity
D_O2 = 2e-5;%Feective oxygen diffusivity
a = 0.5; %transfer coefficent 
j_0 = 0.1; %Exchange current density 
A_SOFC = 9e7; %lectrolyte constant
G_act = 100000; %electrolyte activation energy 
t_m = 0.00002; %electrolyte thickness
t_a = 50;%anode thickness
t_c = 0.0008;%cathode thickess
R = 8.314;%Gas constant
F = 96485;%Faraday constant
j = 5000; %Current density
%-------------------------------------------------------------------------

%ohmic voltage loss 
n_ohmic = j * ((t_m*T)/(A_SOFC*exp(-(G_act/(R*T)))));

%cathode overvoltage
n_cathode = ((R*T)/(4*a*F))*log(j/((j_0*p_c)*((x_O2_Id - t_c)*((j*R*T)/4*F*p_c*D_O2))));


%V = operating voltage of fuel cell
V = E_thermo - n_ohmic - n_cathode ; 

The value for n_cathode is meant to be 0.158V

[Nathaniel Porter]

Original equation above wondering if the use of log is affecting the equation

[David Hill]

No, but your equation is wrong

n_cathode = R*T/(4*a*F)*log(j/(j_0*p_c*(x_O2_Id - t_c*j*R*T/(4*F*p_c*D_O2))));%division is only for t_c*j*R*t not (x_O2_Id - t_c*j*R*T)

[Nathaniel Porter]

Thank youu