Graphene oxide synthesis using microwave-assisted vs. modified Hummer's methods: Efficient fillers for improved ionic conductivity and suppressed methanol permeability in alkaline methanol fuel cell electrolytes

This research investigates the structure and characteristics of microwave-assisted graphene oxide (denoted as MGO) nanofillers and their effect as membrane electrolyte assembly for direct alkaline methanol fuel cell (DAMFC). Two types of GO nanosheets are fabricated: MGO and modified Hummer's method (denoted as NGO). The MGO contained less oxygen (i.e. higher C/O ratio) and higher D/G band ratio than NGO, indicating the microwave method yielded less hydrophilic GO with more sp3 C-C bonds than NGO sample. The shorter reaction time (20 min) of the microwave method also generated larger GO sizes than the conventional method. The MGO contained less ether groups and more resistant to thermal degradation than NGO. One percent GO nanofillers are incorporated into polybenzimidazole (PBI) to form composite membranes, which are subsequently doped with KOH. The PBI/NGO had the highest conductivity while the PBI/MGO had the lowest permeability among the three membranes. DAMFC equipped with PBI/NGO and PBI/MGO electrolytes resulted in peak power densities of 310 and 277 mW cm−2 at 80 °C, respectively. These demonstrated power densities are significantly higher than those reported in literature. Considering the short time and facile method for MGO synthetic process, this microwave-assisted GO has potential as fillers into composite membranes.