A new biopolymer based on chitosan and k-carrageenan with the addition of mesoporous phosphoric acid (mPTA) filler was used as an electrolyte membrane for Direct Methanol Fuel Cell (DMFC) applications. Electrolyte membranes of pure solution of chitosan, k-carrageenan, and various compositions of chitosan/k-carrageenan (Cs/k-Car) (80/40, 90/30, 100/20 mL) were carried out to determine the composition of chitosan/k-carrageenan optimal. The optimum chitosan/k-carrageenan membrane is Cs/k-Car 80/40 which has a tensile strength of 22.00 MPa and a methanol permeability of 14.33 x 10-6 cm2/s. Membrane Cs/k-Car 80/40 was then added with variations of mesoporous phosphotungstic acid (mPTA) filler (0.05, 0.1, 0.15, 0.2 and 0.25 %) to determine the optimum membrane electrolyte. The chitosan/k-carrageenan/mPTA 0,2% (Cs/k-Car/mPTA 0.2%) electrolyte membrane is the most optimum electrolyte membrane which has a proton conductivity of 12 x 10-3 S/cm and a methanol permeability of 7.64 x 10-6 cm2/s so it is expected to be the most suitable electrolyte membrane for DMFC application. Key words : Electrolyte membrane, chitosan, k-carrageenan, mesoporous phosphoric acid (mPTA), DMFC

In this study, chitosan (Chi), alginate (Alg), and mesoporous phosphotungstic acid (mPTA) were used as electrolyte membrane materials for DMFC. Chi and Alg will be crosslinked with mPTA filler to improve the performance of the electrolyte membrane. Characterizations carried out include tensile tests, methanol permeability, and proton conductivity. The results of the tensile test showed that the Chi-Alg(3:1) membrane had a higher tensile strength value (26.64 N/mm2) than the pure chitosan membrane (11.97 N/mm2). The results of methanol permeability show that the Chi-Alg(3:1)/mPTA(2.0%) membrane has a lower methanol permeability value (8.17 × 10-6 cm2 s-1) and a relatively high proton conductivity value, (45.8 × 10-3 S cm-1). Chi-Alg/mPTA membrane, simplicity of the used simple preparation method and the cost reduction can be applied as an electrolyte membrane for DMFC.