Trying to understand why my graphs are all flipped

Question

Nathaniel Porter 2022-3-14

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https://ww2.mathworks.cn/matlabcentral/answers/1671654-trying-to-understand-why-my-graphs-are-all-flipped

回答： Image Analyst 2024-8-26

My ohmic overpotential curve, concentration overpotential curve and cell j-v curve are suppose to be flipped meaning my voltage is meant to decrease when my current density increases (negative gradient)

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(0.0e-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(j/i0_a);%activation potential at anode

V_act_anode = abs(V_act_a);

display(V_act_anode)

V_act_anode = 1×15

Inf 0.2616 0.2450 0.2353 0.2284 0.2230 0.2187 0.2150 0.2118 0.2090 0.2065 0.2042 0.2021 0.2002 0.1984

%Cathode

V_act_c = (R*T)/(a_cathode*n_cathode*F)*log(j/i0_c);%activation potential at cathode

V_act_cathode = abs(V_act_c);

display(V_act_cathode)

V_act_cathode = 1×15

Inf 0.2698 0.2612 0.2561 0.2525 0.2498 0.2475 0.2456 0.2439 0.2425 0.2411 0.2400 0.2389 0.2379 0.2370

%Total activation overpotential

V_act = V_act_cathode + V_act_anode;

display(V_act)

V_act = 1×15

Inf 0.5313 0.5061 0.4914 0.4809 0.4728 0.4662 0.4606 0.4557 0.4514 0.4476 0.4441 0.4410 0.4381 0.4354

%J-V curve

figure

plot(j,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 = j .* R_in;%ohmic overpotential of cell

display(V_ohm)

V_ohm = 1×15

0 0.0003 0.0005 0.0007 0.0010 0.0013 0.0015 0.0018 0.0020 0.0022 0.0025 0.0028 0.0030 0.0033 0.0035

%J-V curve

figure

plot(j,V_ohm)

title('J-V ohmic curve')

xlabel('Current density')

ylabel('Ohmic overpotential')

%--------------------------------------------------------------------------

%Determining glucose concentration

%Anode

J_diff_anode = j/(n_anode*F);%diffusion flux of reactants

display(J_diff_anode)

J_diff_anode = 1×15

1.0e-08 * 0 0.0259 0.0518 0.0777 0.1036 0.1296 0.1555 0.1814 0.2073 0.2332 0.2591 0.2850 0.3109 0.3368 0.3628

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 = j/(n_cathode*F);%diffusion flux of reactants

display(J_diff_cathode)

J_diff_cathode = 1×15

1.0e-08 * 0 0.0130 0.0259 0.0389 0.0518 0.0648 0.0777 0.0907 0.1036 0.1166 0.1296 0.1425 0.1555 0.1684 0.1814

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 = 1×15

1.0e-05 * 0.0017 0.0159 0.0302 0.0444 0.0586 0.0728 0.0871 0.1013 0.1155 0.1297 0.1440 0.1582 0.1724 0.1866 0.2009

%--------------------------------------------------------------------------

%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));

%concentration overpotential at cathode

V_conc_cathode = (R*T)/(n_cathode*F)*log(i_L_c./(i_L_c-j));

%concentration overpotential

V_conc =V_conc_cathode + V_conc_anode;

%J-V curve

figure

plot(j,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(j,V_cell)

title('J-V curve')

xlabel('Current density')

ylabel('Cell voltage')

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显示 -1更早的评论隐藏 -1更早的评论

Khilmi 2024-8-26

hi have you found the solution?

If so, would you like to share the solution with me, because I am experiencing the same problem as you. all my graphs are upside down and I don't understand how to solve it. I am very grateful for your answer. Thanks!

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Answer 1

vidyesh 2023-10-19

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1671654-trying-to-understand-why-my-graphs-are-all-flipped#answer_1336329

编辑：vidyesh 2023-11-29

在 MATLAB Online 中打开

Hi Nathaniel,

Based on my understanding, you would like to know why your graphs are increasing when plotted instead of decreasing.

The relationship between Ohmic Potential and Current Density in the code is linear.

V_ohm = j .* R_in;

‘R_in' is a constant and 'V_ohmic' is the product of 'j' and a constant value. Consequently, Ohmic Potential naturally increases as Current Density increases.

On the other hand, the relationships between Concentration Overpotential and Current Density, as well as Cell Voltage and Current Density, are not linear. However, both of these relationships are directly proportional to Current Density, as indicated by the formulas used in the code.

To ensure accurate calculations, it is recommended to verify the correctness of the equations employed in the code.

Hope this answer helps.