Hydroxide-ion selective electrolytes based on a polybenzimidazole/graphene oxide composite membrane

The objectives of this work are to prepare and characterize poly[2,2′-m-(phenylene)-5,5′-bibenzimidazole]/graphene oxide (PBI/GO) solid electrolyte for direct alcohol alkaline fuel cell (DAAFC) applications. GO nanosheets are coated onto a PBI surface using a spin coater to construct the PBI/GO composite membrane. The PBI/GO composite membrane exhibits an ionic conductivity of 2.53 × 10⁻² S cm⁻¹ at 80 °C, which is improved by 72–93% when compared with the pure PBI membrane. In addition, the methanol permeability is reduced by 18–25% by incorporating GO onto the PBI top surface. The peak power density (P_max) of the PBI/GO electrolyte reaches 200 mW cm⁻² when using alkaline methanol as fuel with Pt-based catalysts, or 120 mW cm⁻² when fed with an ethanol and alkaline solution mixture at 80 °C. Replacing the Pt-based catalysts with Hypermec™ catalysts resulted in P_max of 40 and 100 mW cm⁻², for methanol and ethanol fuel cells, respectively. These superior DAAFC power outputs are ascribed to the improved anion conduction of the KOH doped GO and the suppressed methanol cross-over from high aspect ratio GO as the alcohol barrier layer.