The Reynolds number was calculated from Eq. 32, in which the permeability of the porous electrode was used as a reference length scale. The permeability was set as K = 2.1 × 10 -11 m 2 based on the commonly used Freudenberg H23 carbon paper properties. Although this is an acceptable range for the purpose of the current study, this value should be chosen more accurately based on the permeability of TPMS structures in the pore scale in future studies . Assuming the physical properties of water for the electrolyte (ρ = 10 3 kg.m -3 , µ = 10 -4 Pa.s) and the reference inlet velocity of 0.25 m.s -1 , the Reynolds number was calculated as Re = 1. Moreover, by assuming a representative unit length scale of 1 mm for considering the flow relaxation over two TPMS unit cells, the base Darcy number was calculated as 2.1 × 10 -5 for the carbon paper. As a result, in the 2D simulations, the Darcy number was varied as Da ∈ {10 -5 , 10 -4 , 5 × 10 -4 } to account for the base case as well as to test various cases for featuring higher permeabilities. To facilitate the convergence of the flow solver, the 3D simulations were performed using the highest Darcy number, Da = 5×10 -4 .