High-Performance Proton Exchange Membrane Fuel Cell Membranes from Sulfonated Chitosan Enhanced with Sulfonated Titanium Dioxide and Sulfonated Silicon Dioxide Nanoparticles

Sulfonated chitosan (SCS) was synthesized using chlorosulfonic acid and characterized using XRD, FTIR, SEM, TGA, DTG, and 1HNMR, which were used for the determination of the degree of sulfonation (DS), ionic exchange capacity (IEC), and sulfur content (Sc). The studied parameter for the preparation of SCS was the quantity of CLSO3H. The formed SCS results proved that the highest DS, IEC, and Sc were 98.36%, 0.61296 mmol/g, and 1.9615%, respectively, achieved using 15 ml of CLSO3H. Seven membranes were prepared with and without sulfonated nanoparticles, including individual sulfonated titanium dioxide (STiO₂), sulfonated silicon dioxide (SSiO₂), or a combination of both. The glutaraldehyde was used as a cross-linker in the preparation of the membranes. The sixth and seventh (M6 and M7) membranes demonstrated the highest performance. M6, cross-linked with 0.5 M sulfuric acid, exhibited a current density of 70.3 mA/cm², a maximum power density of 91 mW/cm², and a low cell resistance of 3 Ω cm² at 50 mA/cm². In contrast, M7, cross-linked with 0.5% glutaraldehyde, showed lower performance, with a current density of 39 mA/cm², a maximum power density of 47 mW/cm², and a higher cell resistance of 14 Ω cm². These results indicate that the membrane using sulfuric acid in M6 outperforms the one cross-linked with glutaraldehyde (M7) regarding electrical performance. However, M7 demonstrated greater stability during prolonged operation, demonstrating its potential for long-term durability applications. A subset of these membranes (M1 and M7) was characterized by FTIR, XRD, SEM, TGA, DTG, 1HNMR, proton conductivity, water uptake, swelling ratio, and mechanical properties. The optimum membrane performance was M7, which was prepared using a mixture of SCS with STiO₂/SSiO₂ and cross-linked with 0.5% glutaraldehyde. The membrane component ratios were 1 g: 0.6 g: 0.6 g. The M7 was characterized by a maximum power density of 47 mW/cm² at a current density of 39 mA/cm² with a cell resistance of 14 Ω cm². The proton conductivity of M7 was 6.9 × 10⁻⁴ S/cm, the IEC was 0.72mmol/g, the water uptake and swelling ratios were 31.4% and 19.04%, respectively, and the mechanical strength and the elongation at break percentage were 13.826 MPa and 10.766%, respectively. These results demonstrate that M7 strikes a balance between performance and stability, making it a promising candidate for fuel cell applications. The objective is to synthesize sulfonated chitosan (SCS) powder and use it with sulfonated titanium dioxide and silicon dioxide nanoparticles to fabricate composite membranes for proton exchange membrane fuel cell applications. The goal is to improve the membranes' performance and stability by optimizing their composition and cross-linking method. Testing in fuel cells confirmed their effective performance and durability, highlighting their potential for clean energy applications.