## 2 Materials and Methods  
### Preparation of Pore-Filling Membranes  
AEMs with a thickness of 95 \(\upmu\)m were fabricated via a pore-filling method. The proprietary material, PP, with a thickness of 95 \(\upmu\)m and a porosity of 49.4% was used as the porous substrate and was provided by a confidential source. The pore size was analyzed by using field emission-scanning electron microscopy (FE-SEM, SIGMA500, [PERSON], Oberkochen, Germany), exhibiting the pore size approximately 50-200 nm, as shown in Figure 1.  
(Vinylbenzyl) trimethylammonium chloride (designated as E3; Sigma-Aldrich, St. Louis, MO, USA) served as the anion-conducting monomer. The cross-linking monomers employed were 1,3,5-triacryloylhexahydro-1,3,5-triazine (designated as C10; Sigma-Aldrich, St. Louis, MO, USA) and trimethylopropane trimethacrylate (designated as C11; Sigma  
Figure 1: Cross-sectional and surface FE-SEM image: (**a**) 95 \(\upmu\)m thick, porous PP substrate utilized in this study; (**b,c**) pore size analysis.  
Aldrich, St. Louis, MO, USA). Additionally, 2-hydroxy-2-methylpropiophenone (designated as P1; Sigma-Aldrich, St. Louis, MO, USA) was utilized as the photo-initiator. Table 1 summarizes the chemical information of the monomers.  
Before filling various monomer solutions into PP substrates, the organic and inorganic contaminants in the porous PP substrates were eliminated by soaking in EtOH (99.5%, Sigma-Aldrich, St. Louis, MO, USA) for 15 min, followed by drying. After this, the cleaned hydrophobic porous PP substrate was pretreated with a 0.5 wt.% solution of sodium dodecylbenzenesulfonate (Sigma-Aldrich, St. Louis, MO, USA) in deionized water (D.I. water) to impart hydrophilic characteristics. To fabricate pore-filling anion-exchange membranes (PFAEMs) based on E3, C10, and C11 monomers, E3 monomers were first dissolved in a 50:50 D.I. water/EtOH solvents to prepare a 50 wt.% monomer solution. The electrolyte (E3) monomer solution was stirred for 1 h. Subsequently, C10 or C11 monomers were added to the E3 monomer solution. The resulting solutions, containing electrolyte and cross-linking (C10 or C11) monomers, were stirred for an additional hour. To initiate the polymerization reaction using a 1500 W wide-range UV light, 2 wt.% of P1 (relative to the total weight of electrolyte and cross-linker monomers) was added. The fabricated monomer solution for pore-filling had a 20:1 mole ratio of electrolyte to cross-linker monomer. The hydrophilic PP substrates were immersed in the fabricated monomer solution to allow penetration into the pores. The monomer solution-filled PP substrates were then sandwiched between silica-coated polyethylene (PET) films. The excess solution was squeezed out to remove residual monomers and oxygen bubbles. The UV light was applied for 40 min to initiate in situ cross-linking. Afterward, the PET films were delaminated, and the PFAEMs were washed to remove any residual polymer. The procedures for membrane fabrication are detailed in Figure 2.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Code** & **Monomer** & **Structural Formula** & **3D Model 1.** & **MW (g mol\({}^{-1}\))** \\ \hline E3 & (Vinylbenzyl) trimethylammonium chloride & & 211.73 \\ C10 & 1,3,5-Triacrylamide & & 249.27 \\ C11 & Trimethylolpropane trimethacrylate & & 338.40 \\ \hline \end{tabular} \({}^{1}\) Grey, red, blue, and white atoms represent carbon, oxygen, nitrogen, and hydrogen, respectively.  
\end{table}
Table 1: Chemical information of the monomers used in this study.