Bio-functionalized hybrid nanocomposite membranes for direct methanol fuel cells

Abstract

Bio-molecules are responsible for rapid proton conduction in biological systems. In view of this, hybrid nanocomposite membranes are prepared by incorporating amino acid functionalized titaninum dioxide (AA–TiO₂) bio-hybrid nanoparticles into a polyvinylalcohol (PVA) matrix. Sequential binary cross-linking of PVA with sulfosuccinic acid (SSA) and glutaraldehyde (GA) provides adequate mechanical strength and thermal stability. TiO₂ nanoparticles are functionalized with three different amino acids (AAs) namely glycine, phenyl alanine and lysine. AA functionalization to TiO₂ improves the interaction and degree of adhesion between organic–inorganic phases leading to a homogenous dispersion when used as an additive in PVA. Interfacial interactions between AA–TiO₂ and PVA are confirmed by Fourier transform infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM), thermogravimetry (TG) and UV-Visible spectral analyses. Elemental mapping of the PVA–LY–TiO₂ hybrid nanocomposite membrane confirms the incorporation of AA–TiO₂ bio-hybrid nanoparticles within the PVA matrix. The suitability of these membranes as electrolytes for direct methanol fuel cells (DMFCs) has been demonstrated through assessment of proton conductivity and methanol permeability. The zwitterion (dipolar ion) architecture created by the AA–TiO₂ bio-hybrid nanoparticles substantially facilitates proton conduction through acid–base pairs analogous to biological systems and simultaneously eases methanol permeation. The optimized membrane PVA–lysine–TiO₂ is used as an electrolyte in a DMFC which delivers nearly a two-fold higher peak power density of 58 mW cm⁻², compared to the pristine PVA membrane.