Development of low-cost nafion-lignin composite conductive membranes for application in direct methanol fuel cells

The advantages of the direct methanol fuel cell (DMFC) are its high energy density, simple size with a compact fuel tank and effortless storage and transportation, making it one of the leading fuel cell types. However, the commercialisation of this technology is hampered by a number of issues, including methanol crossover and the high cost of Nafion membranes. In this study, an environmentally friendly composite membrane Nafion-lignosulfonate (LS) with merits of high proton conductivity and low methanol permeability was prepared by simple solution casting. An Electrochemical Impedance Spectroscopy (EIS) approach was used to determine the proton conductivity of the composite membranes at room temperature. A composite membrane with 10 wt% filler (rN/LS10) is found to show the best selectivity of 1.10 × 104 S s cm−3. In addition, this composite membrane shows a proton conductivity of 0.92 mS cm−1 and a permeability to methanol of 8.34 × 10−8 cm2 s−1. A single-cell performance test confirms that rN/LS10 shows a power density of 11.7 mW/cm2, which is a 20.9% improvement over commercial N117 at room temperature. Compared to N117, rN/LS10 shows acceptable durability for a fuel cell operated at 0.3 V for 24 h with a decay rate of 0.51 mA cm−2.h−1. More importantly, by reducing the amount of Nafion polymer used, the cost of the rN/LS composite membrane can be reduced by 8.02% compared to commercially N117 while maintaining stability and performance. On the road to commercialisation, the Nafion-lignosulfonate composite membrane is, therefore, a competitive choice for DMFCs.