Characterization of direct methanol fuel cell (DMFC) applications with H 2SO 4 modified chitosan membrane

Abstract

Chitosan (Chs) flakes were prepared from chitin materials that were extracted from the exoskeleton of Cape rock lobsters in South Africa. The Chs flakes were prepared into membranes and the Chs membranes were modified by cross-linking with H 2SO 4. The cross-linked Chs membranes were characterized for the application in direct methanol fuel cells. The Chs membrane characteristics such as water uptake, thermal stability, proton resistance and methanol permeability were compared to that of high performance conventional Nafion 117 membranes. Under the temperature range studied 20–60 °C, the membrane water uptake for Chs was found to be higher than that of Nafion. Thermal analysis revealed that Chs membranes could withstand temperature as high as 230 °C whereas Nafion 117 membranes were stable to 320 °C under nitrogen. Nafion 117 membranes were found to exhibit high proton resistance of 284 s cm −1 than Chs membranes of 204 s cm −1. The proton fluxes across the membranes were 2.73 mol cm −2 s −1 for Chs- and 1.12 mol cm −2 s −1 Nafion membranes. Methanol (MeOH) permeability through Chs membrane was less, 1.4 × 10 −6 cm 2 s −1 for Chs membranes and 3.9 × 10 −6 cm 2 s −1 for Nafion 117 membranes at 20 °C. Chs and Nafion membranes were fabricated into membrane electrode assemblies (MAE) and their performances measure in a free-breathing commercial single cell DMFC. The Nafion membranes showed a better performance as the power density determined for Nafion membranes of 0.0075 W cm −2 was 2.7 times higher than in the case of Chs MEA.