Ω ratio of electrode thickness []

## **Subscripts, superscripts**


*Solid Oxide Steam Electrolyzer: Gas Diffusion Steers the Design of Electrodes DOI: http://dx.doi.org/10.5772/intechopen.90352*


## **Appendix**

Contrary to the cathode, the changes of grain diameter gradient do not influence the electrochemical performance of the anode. However, its current production profile is consistently similar to the cathodic one. This means that specific attention

Several aspects have been neglected in the present work and should be investigated to complete this approach and give global vision of the mechanisms that govern a SOEC response, e.g., the ohmic resistance due the dense ceramic membrane can be minimized using metal support technologies. In addition, the contact resistances shall be taken into consideration since they are a key parameter when optimizing the configuration of current collectors and will allow this model to be

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should be given to the cathode microstructure.

compared to experimental data of total SRU response.

**Conflict of interest**

*Electrodialysis*

No conflict of interest.

**Acronyms and abbreviations**

*C* concentration [mol m<sup>3</sup>

*D* diffusion coefficient [m2 s

*dg* mean grain diameter [m] *dp* mean pore diameter [m] *E* Nernst potential [V] *i* current density [A m<sup>3</sup>

L electrode thickness [μm]

*M* molar mass [kg mol<sup>1</sup>

*α* factor of symmetry []

*ϕ* electrical potential [V]

Ω ratio of electrode thickness []

*P* pressure [Pa]

*V* voltage [V]

*ε* porosity [] *η* overpotential [V] *σ* conductivity [S m<sup>1</sup>

*τ* tortuosity []

**Subscripts, superscripts**

0 Standard

*i* type of conductor

**Greek**

**110**

*T* temperature [K]

*i*<sup>0</sup> exchange current density [A m<sup>3</sup>

n normal derivative vector [m]

*Q* volumic current source [A m<sup>3</sup>

x relative abscissa of electrode thickness [m]

*Y* molar fraction or volume fraction []

*β* fick diffusion form coefficient [] Γ mass source term [*mol m<sup>3</sup>* s

The diffusion coefficient for binary mixture of gases may be estimated from Fuller, Schettler, and Giddings relation with values coefficients for different molecules tabulated in [34]:

$$D\_{H\_2O\_sH\_2} = 3.16 \times 10^{-8} \frac{T^{1.75} \left(\frac{1000}{18} + \frac{1000}{2}\right)^{1/2}}{P \left(\left(7.06 \times 10^{-6}\right)^{1/3} + \left(12.7 \times 10^{-6}\right)^{1/3}\right)^2} \tag{26}$$

$$D\_{O\_2N\_2} = 3.16 \times 10^{-8} \frac{T^{1.75} \left(\frac{1000}{28} + \frac{1000}{32}\right)^{1/2}}{P \left(\left(17.9 \times 10^{-6}\right)^{1/3} + \left(16.6 \times 10^{-6}\right)^{1/3}\right)^2} \tag{27}$$

*Electrodialysis*
