A. Paneri, S. Moghaddam
University of Florida,
Keywords: graphene oxide, proton exchange membrane, direct methanol fuel cell
Summary:Development of a proton exchange membrane (PEM) with insignificant methanol permeability at highly concentrated methanol supply is considered a major advancement in the direct methanol fuel cell (DMFC) technology. Here, we investigate the potential of graphene-based membranes for achieving this objective. A membrane is prepared through the lamination of graphene-oxide (GO) nanoplatelets and its transport characteristics are studied. It is determined that the two key parameters that dictate the transport characteristics of a GO laminate are the GO oxidation level and flake size. Through a parametric study, it is determined that at a constant oxidation level methanol permeability decreases linearly with increasing the GO mean flake size while changes in proton conductivity remain insignificant. This behavior is attributed to difference in adopted conduction pathways of protons and methanol molecules. With increasing the oxidation level, proliferation of surface defects is deductively reasoned to be the dominant factor responsible for a large increase in the measured methanol permeability. The proton conductivity is also significantly increased with increasing the oxidation level because of greater number of ion exchange sites, shortened transport pathway and increased GO flakes inter-layer spacing. Based on the interaction of its surface oxidative groups with the aqueous methanol solution, GO is found to sustain its structural stability and conductivity in a better way than Nafion when the methanol concentration is increased. Direct methanol fuel cell measurements of the membrane at high fuel concentrations showed almost no drop in the open circuit potential (OCP) and significant improvements in power density compared to that of a Nafion membrane.