Acid catalysed cross-linking of poly vinyl alcohol (PVA) by glutaraldehyde: effect of crosslink density on the characteristics of PVA membranes used in single chambered microbial fuel cells

Abstract

In the present study, acid catalysed cross-linking of poly vinyl alcohol (PVA) with varying concentrations of glutaraldehyde was analyzed and the cross-linked PVAs were utilized as membrane separators in single chambered microbial fuel cells (MFCs). PVA with varying concentrations (1, 2, 4 and 6%) of glutaraldehyde has resulted in a respective 2.8, 5.6, 32 and 34% of degree of cross-linking in PVA1, PVA2, PVA3 and PVA4 membranes. Due to the reduction of available free volume in membranes, progressive improvements in membrane rigidity with impeded membrane porosity were observed with increasing cross-link densities. In succession, proton conductivities of 7.53 × 10⁻³, 8.4 × 10⁻⁴, 1.2 × 10⁻⁴ and 4.5 × 10⁻⁵ S cm⁻¹ were observed from the respective PVA1, PVA2, PVA3, and PVA4 membranes. The increased cross-link density enhanced the mechanical strength but reduced other membrane properties such as water uptake and proton conductivities of the membranes. Further, the cast membranes were assembled as MEAs in open air cathode MFCs where, a maximum power and current density of 119.13 ± 6 mW m⁻² and 447.81 ± 18 mA m⁻² were observed from PVA3 fitted MFC, using mixed firmicutes as biocatalysts. With increased cross-link density, higher ohmic resistances were observed in MFCs, but due to lower oxygen diffusion in the anode, increased performance was observed from highly cross-linked membranes. Electrogenic firmicutes revealed an overall ∼93.45% of COD removal in 27 days of operation, indicating the efficiency of the respective membranes as separators in MFCs. In general, the study depicts the relevance of different acid catalysed cross-linked PVA membranes in bio-energy conversion from microbial fuel cells.