Starting my x-axis values not from zero

Trying to start x-axis which is my current density(j) values from the value 7e-3. Can anyone help out with this.

clc;
clear;
%Variables
m=15;
k = 15;
a_anode = 0.54; %transfer coefficient at anode
a_cathode = 0.52; %transfer coeffiecent at cathode
R = 8.314;%Gas constant
F = 96485;%Faraday constant
T = 300; %Temperature of cell
A_electrodes = 2; %area of electrodes
R_in = A_electrodes*2.5; %Internal resistance of the cell
n_anode = 2; %moles per reactant at the anode
n_cathode =4;%moles per reactant at the cathode
D_anode = 2.4e-6; %diffusion coefficient of glucose in bird
D_cathode = 1.8e-5;%diffusion coefficient of oxygen in bird
d_l_a = 0.005; %diffsuion layer thickness anode
d_l_c= 0.005 ;%diffsuion layer thickness cathode
j = linspace(0.005e-3,0.7e-3,k);%Current density of the cell
jT = j';
C_s_anode = 5.55e-8; %concentration of reactant at the catalyst
C_s_cathode = 1.71e-8; %concentration of reactant at the catalyst
A_anode = 2; %active area of electrode
A_cathode = 2; %active area of electrode
row = 0.005; %diffusion distance
e = 0.4;%porosity of the structure
D_ij_anode = 9.5e-6; %binary diffusion coefficient(glucose in human dura mater)
D_ij_cathode = 1.8e-5;%Diffsuion coefficent of oxyegen in plain medium
i_ref_a = 3.5e-3; %anode reference exchange current density
L_anode = 0.3; %catalyst loading anode
P_anode = 2130; %Pressure at anode
P_ref_anode = 1.2; %reference pressure at the anode
T_ref_anode = 298; %reference temperature at anode
i_ref_c = 1.95e5; %anode reference exchange current density
L_cathode = 0.3; %catalyst loading anode
P_cathode = 50; %Pressure at anode
P_ref_cathode = 700; %reference pressure at the anode
T_ref_cathode = 298; %reference temperature at anode
%% 
%Effective exchange current density
%Anode
i0_a = i_ref_a * A_anode * L_anode *(P_anode/P_ref_anode)^0.5 *(-(130/R*T)*(1-(T/T_ref_anode)));

%Cathode
i0_c = i_ref_c * A_cathode * L_cathode *(P_cathode/P_ref_cathode)^1 *(-(66/R*T)*(1-(T/T_ref_cathode)));
%% 
%Activation Overpotential 
%Anode
V_act_a = (R*T)/(a_anode*n_anode*F)*log(jT/i0_a);%activation potential at anode
V_act_anode = abs(V_act_a);
display(V_act_anode)
%Cathode
V_act_c = (R*T)/(a_cathode*n_cathode*F)*log(jT/i0_c);%activation potential at cathode
V_act_cathode = abs(V_act_c);
display(V_act_cathode)

%Total activation overpotential
V_act = V_act_cathode + V_act_anode;
display(V_act)
%J-V curve
figure
plot(jT,V_act)
title('J-V Vact curve')
xlabel('Current density')
ylabel('Activation overpotential')
%% 
%Ohmic overpotential
%R_cell_anode = Rin .* A_anode; %resisitance of fuel cell
%R_cell_cathode = Rin .* A_cathode; %resisitance of fuel cell
%R_cell = R_cell_anode + R_cell_cathode;
V_ohm = jT .* (R_in);%ohmic overpotential of cell
display(V_ohm)
%J-V curve
figure
plot(jT,V_ohm)
title('J-V ohmic curve')
xlabel('Current density')
ylabel('Ohmic overpotential')
%% 
%Determining glucose concentration
%Anode
J_diff_anode = jT/(n_anode*F);%diffusion flux of reactants
display(J_diff_anode)

D_eff_anode = (e^1.5) * D_ij_anode;%effective reactant diffusivity
display(D_eff_anode)

C_b_anode = -((J_diff_anode*row)/-D_eff_anode)+ C_s_anode;
C_b_anodeT = C_b_anode';
 
Glucose_conc = (C_b_anodeT * 180.156)*100000;
%Cathode
J_diff_cathode = jT/(n_cathode*F);%diffusion flux of reactants
display(J_diff_cathode)

D_eff_cathode = (e^1.5) * D_ij_cathode;%effective reactant diffusivity
display(D_eff_cathode)

C_b_cathode  = -((J_diff_cathode*row)/-D_eff_cathode)+ C_s_cathode;
%bulk concentration of reactant(oxygen)
display(C_b_cathode)
%% 
%Concentration overpotential

%limiting current at anode
i_L_a = (n_anode*F*D_eff_anode*(C_b_anode/d_l_a));
%limiting current at cathode
i_L_c = (n_cathode*F*D_eff_cathode*(C_b_cathode/d_l_c));

%concentration overpotential at anode
%V_conc_anode = (R*T)/(n_anode*F)*log(i_L_a./(i_L_a-j));
V_conc_anode = (R*T)/(n_anode*F)*log(C_b_anode/C_s_anode);
%concentration overpotential at cathode
%V_conc_cathode = (R*T)/(n_cathode*F)*log(i_L_c./(i_L_c-j));
V_conc_cathode = (R*T)/(n_cathode*F)*log(C_b_cathode/C_s_cathode);

%c_anode = (R*T)/(n_anode*F)*log(1/1+a_anode);
%c_cathode = (R*T)/(n_cathode*F)*log(1/1+a_cathode);
%V_conc_anode = c_anode .*log(i_L_a./i_L_a-j);
%V_conc_cathode = c_cathode .*log(i_L_c./i_L_c-j);

%concentration overpotential
V_conc = V_conc_cathode + V_conc_anode;
%J-V curve
figure
plot(jT,V_conc)
title('J-V Vconc curve')
xlabel('Current density')
ylabel('Cocnetration overpotential')
%% 
%Cell potential
Et =1.3; %thermodynamic potential of fuel cell

%Fuel cell voltage
V_cell1 = Et - V_act - V_conc - V_ohm; 
V_cell = abs(V_cell1);
%% 
%Power of fuel cell

P_cell = V_cell .* j;
P_cell1 = abs(P_cell);
%% 
%J-V curve
figure
plot(jT,V_cell)
title('J-V curve')
xlabel('Current density')
ylabel('Cell voltage')

Answer 1

[Simon Chan]

Modify like the following for each plot.

figure
h = plot(jT,V_cell);            % Get the data (Modify)
ax=gca;                         % Get the handle (Modify)
title('J-V curve')
xlabel('Current density')
ylabel('Cell voltage')
ax.XTick(1) = h.XData(1);       % <--- Add this line

Answer 2

[Star Strider]

‘Trying to start x-axis which is my current density(j) values from the value 7e-3. Can anyone help out with this.’

Probably not, at least not without some clarification. The independent variable is defined as the transpose of ‘j’, defined here as:

j = linspace(0.005e-3,0.7e-3,k);%Current density of the cell

so ‘7e-3’ is outside the xlim range, and ‘7e-4’ is the upper end of the range.

Please clarify what you want to do.

%Variables
m=15;
k = 15;
a_anode = 0.54; %transfer coefficient at anode
a_cathode = 0.52; %transfer coeffiecent at cathode
R = 8.314;%Gas constant
F = 96485;%Faraday constant
T = 300; %Temperature of cell
A_electrodes = 2; %area of electrodes
R_in = A_electrodes*2.5; %Internal resistance of the cell
n_anode = 2; %moles per reactant at the anode
n_cathode =4;%moles per reactant at the cathode
D_anode = 2.4e-6; %diffusion coefficient of glucose in bird
D_cathode = 1.8e-5;%diffusion coefficient of oxygen in bird
d_l_a = 0.005; %diffsuion layer thickness anode
d_l_c= 0.005 ;%diffsuion layer thickness cathode
j = linspace(0.005e-3,0.7e-3,k);%Current density of the cell
jT = j';
C_s_anode = 5.55e-8; %concentration of reactant at the catalyst
C_s_cathode = 1.71e-8; %concentration of reactant at the catalyst
A_anode = 2; %active area of electrode
A_cathode = 2; %active area of electrode
row = 0.005; %diffusion distance
e = 0.4;%porosity of the structure
D_ij_anode = 9.5e-6; %binary diffusion coefficient(glucose in human dura mater)
D_ij_cathode = 1.8e-5;%Diffsuion coefficent of oxyegen in plain medium
i_ref_a = 3.5e-3; %anode reference exchange current density
L_anode = 0.3; %catalyst loading anode
P_anode = 2130; %Pressure at anode
P_ref_anode = 1.2; %reference pressure at the anode
T_ref_anode = 298; %reference temperature at anode
i_ref_c = 1.95e5; %anode reference exchange current density
L_cathode = 0.3; %catalyst loading anode
P_cathode = 50; %Pressure at anode
P_ref_cathode = 700; %reference pressure at the anode
T_ref_cathode = 298; %reference temperature at anode
%% 
%Effective exchange current density
%Anode
i0_a = i_ref_a * A_anode * L_anode *(P_anode/P_ref_anode)^0.5 *(-(130/R*T)*(1-(T/T_ref_anode)));

%Cathode
i0_c = i_ref_c * A_cathode * L_cathode *(P_cathode/P_ref_cathode)^1 *(-(66/R*T)*(1-(T/T_ref_cathode)));
%% 
%Activation Overpotential 
%Anode
V_act_a = (R*T)/(a_anode*n_anode*F)*log(jT/i0_a);%activation potential at anode
V_act_anode = abs(V_act_a);
display(V_act_anode)

V_act_anode = 15×1

0.3167 0.2594 0.2440 0.2347 0.2280 0.2227 0.2185 0.2148 0.2117 0.2089

%Cathode
V_act_c = (R*T)/(a_cathode*n_cathode*F)*log(jT/i0_c);%activation potential at cathode
V_act_cathode = abs(V_act_c);
display(V_act_cathode)

V_act_cathode = 15×1

0.2984 0.2687 0.2606 0.2558 0.2523 0.2496 0.2474 0.2455 0.2439 0.2424

%Total activation overpotential
V_act = V_act_cathode + V_act_anode;
display(V_act)

V_act = 15×1

0.6151 0.5281 0.5046 0.4904 0.4803 0.4723 0.4658 0.4603 0.4555 0.4513

%J-V curve
figure
plot(jT,V_act)
title('J-V Vact curve')
xlabel('Current density')
ylabel('Activation overpotential')

% xlim([7E-3 max(xlim)])
%% 
%Ohmic overpotential
%R_cell_anode = Rin .* A_anode; %resisitance of fuel cell
%R_cell_cathode = Rin .* A_cathode; %resisitance of fuel cell
%R_cell = R_cell_anode + R_cell_cathode;
V_ohm = jT .* (R_in);%ohmic overpotential of cell
display(V_ohm)

V_ohm = 15×1

0.0000 0.0003 0.0005 0.0008 0.0010 0.0013 0.0015 0.0018 0.0020 0.0023

%J-V curve
figure
plot(jT,V_ohm)
title('J-V ohmic curve')
xlabel('Current density')
ylabel('Ohmic overpotential')

%% 
%Determining glucose concentration
%Anode
J_diff_anode = jT/(n_anode*F);%diffusion flux of reactants
display(J_diff_anode)

J_diff_anode = 15×1

1.0e-08 * 0.0026 0.0283 0.0540 0.0798 0.1055 0.1312 0.1569 0.1827 0.2084 0.2341

D_eff_anode = (e^1.5) * D_ij_anode;%effective reactant diffusivity
display(D_eff_anode)

D_eff_anode = 2.4033e-06

C_b_anode = -((J_diff_anode*row)/-D_eff_anode)+ C_s_anode;
C_b_anodeT = C_b_anode';
 
Glucose_conc = (C_b_anodeT * 180.156)*100000;
%Cathode
J_diff_cathode = jT/(n_cathode*F);%diffusion flux of reactants
display(J_diff_cathode)

J_diff_cathode = 15×1

1.0e-08 * 0.0013 0.0142 0.0270 0.0399 0.0527 0.0656 0.0785 0.0913 0.1042 0.1171

D_eff_cathode = (e^1.5) * D_ij_cathode;%effective reactant diffusivity
display(D_eff_cathode)

D_eff_cathode = 4.5537e-06

C_b_cathode  = -((J_diff_cathode*row)/-D_eff_cathode)+ C_s_cathode;
%bulk concentration of reactant(oxygen)
display(C_b_cathode)

C_b_cathode = 15×1

1.0e-05 * 0.0031 0.0173 0.0314 0.0455 0.0596 0.0738 0.0879 0.1020 0.1161 0.1302

%% 
%Concentration overpotential

%limiting current at anode
i_L_a = (n_anode*F*D_eff_anode*(C_b_anode/d_l_a));
%limiting current at cathode
i_L_c = (n_cathode*F*D_eff_cathode*(C_b_cathode/d_l_c));

%concentration overpotential at anode
%V_conc_anode = (R*T)/(n_anode*F)*log(i_L_a./(i_L_a-j));
V_conc_anode = (R*T)/(n_anode*F)*log(C_b_anode/C_s_anode);
%concentration overpotential at cathode
%V_conc_cathode = (R*T)/(n_cathode*F)*log(i_L_c./(i_L_c-j));
V_conc_cathode = (R*T)/(n_cathode*F)*log(C_b_cathode/C_s_cathode);

%c_anode = (R*T)/(n_anode*F)*log(1/1+a_anode);
%c_cathode = (R*T)/(n_cathode*F)*log(1/1+a_cathode);
%V_conc_anode = c_anode .*log(i_L_a./i_L_a-j);
%V_conc_cathode = c_cathode .*log(i_L_c./i_L_c-j);

%concentration overpotential
V_conc = V_conc_cathode + V_conc_anode;
%J-V curve
figure
plot(jT,V_conc)
title('J-V Vconc curve')
xlabel('Current density')
ylabel('Cocnetration overpotential')

%% 
%Cell potential
Et =1.3; %thermodynamic potential of fuel cell

%Fuel cell voltage
V_cell1 = Et - V_act - V_conc - V_ohm; 
V_cell = abs(V_cell1);
%% 
%Power of fuel cell

P_cell = V_cell .* j;
P_cell1 = abs(P_cell);
%% 
%J-V curve
figure
plot(jT,V_cell)
title('J-V curve')
xlabel('Current density')
ylabel('Cell voltage')

.

[Nathaniel Porter]

I need my graph to be flipped or mirrored somehow right now my two last grpahs in code have a postive gradient whereas I am trying ti achieve a negative graidient

[Star Strider]

If they’re simply not calculated correctly, I would need to see the equations necessary to calculate them. That may be the problem.

Otherwise, one option for each is:

set(gca, 'YDir','reverse')

or something similar, assuming that the idea is to flip them with respect to the y-axis so they look like the first plot.

The other option would be:

set(gca, 'XDir','reverse')

since that would also result in a negative gradient, although a different-appearing plot, shifted left-to-right, not upside-down.

.

[Nathaniel Porter]

I have been trying to upload equations however the forum wont let me and Im not sure why

[Star Strider]

Neither am I.

See if uploading an image of them works.

[Walter Roberson]

You can upload anything if you zip it first.