$L$	Length of geometric (m)	$\alpha$	Electrical transfer coefficient
$W$	Width of geometric (m)	${\sigma }_A$	Specific surface area (${\mathrm{m}}^{-1}$)
$H$	Height of geometric (m)	$\theta$	Excess potential (V)
$u$	Fluid velocity ($\mathrm{m}{\mathrm{s}}^{-1}$)	$\eta$	Overpotential (V)
$I$	Current density ($\mathrm{A}{\mathrm{m}}^{-2}$)	Subscripts and superscripts
$F$	Faraday constant ($\mathrm{96,487} \mathrm{C} {\mathrm{m}\mathrm{o}\mathrm{l}}^{-1}$)	$gdl$	Gas diffusion layer
$j$	Transition current density ($\mathrm{A}{\mathrm{m}}^{-3}$)	$r$	Rib
$M$	Molecular weight ($\mathrm{k}\mathrm{g} {\mathrm{m}\mathrm{o}\mathrm{l}}^{-1}$)	$m$	Membrane
$F_u$	Force term ($\mathrm{k}\mathrm{g}/\left({\mathrm{m}}^2{\mathrm{s}}^2\right)$)	$c$	Gas channel
$w$	Mass fraction (%)	$e$	Electrode
$x_k$	Mole fraction (%)	$H_2$	Hydrogen
$g$	External force ($\mathrm{m} {\mathrm{s}}^{-2}$)	$O_2$	Oxygen
$D$	Mass diffusivity $\left({\mathrm{m}}^2{\mathrm{s}}^{-1}\right)$	$N_2$	Nitrogen
$R$	Universal gas constant (${8.314 \mathrm{m}\mathrm{o}\mathrm{l}}^{-1}{\mathrm{K}}^{-1}$)	$H_{2}O$	Water
$T$	Temperature (K)	$s$	Solid
$C$	Molar concentration ($\mathrm{m}\mathrm{o}\mathrm{l} {\mathrm{m}}^{-3}$)	$a$	Anode
$P$	Pressure (Pa)	$c$	Cathode
$E_{eq}$	Equilibrium potential (V)	$\infty$	Bulk condition
$R_s$	Internal resistance (${\mathsf{\Omega }}^{-1}{\mathrm{c}\mathrm{m}}^2$)	$o$	Standard condition
Greek symbols		$i$	Species index
$\rho$	Density ($\mathrm{k}\mathrm{g} {\mathrm{m}}^{-3}$)	$loc$	Location
$\epsilon$	Porosity	$eff$	Effective
$\mu$	Dynamic viscosity ($\mathrm{k}\mathrm{g} {\mathrm{m}}^{-1}{\mathrm{s}}^{-1}$)	$ref$	Reference
$\kappa$	Permeability (${\mathrm{m}}^2$)	$k$	Species index independently of i
${\beta }_F$	Forchheimer drag option (${\mathrm{k}\mathrm{g}}^{-1}{\mathrm{m}}^4$)	$cl$	Catalytic electrode
$\sigma$	Conductivity ($\mathrm{S} {\mathrm{m}}^{-1}$)	$l$	Liquid
$\varphi$	Phase potential (V)	$f$	Fin