The effect of glycerol on the conductivity of Nafion-free ZrP/PTFE composite membrane electrolytes for direct hydrocarbon fuel cells

Composite membranes composed of zirconium phosphate (ZrP, a proton conductor), and porous polytetrafluoroethylene (PTFE, a mechanical support for ZrP), have been studied as electrolytes for direct hydrocarbon fuel cells that might operate at temperatures approaching 200 °C. The previous literature describes membranes formed by compressing PTFE particles and ZrP particles (conductivity = 10−3 S cm−1). The results reported here show that adding glycerol (GLY) to a reaction mixture of ZrOCl2·8H2O and H3PO4 to form ZrP in situ within the pores of PTFE, produced a membrane (conductivity = 0.02–0.045 S cm−1) that approached the performance of Nafion (conductivity = 0.1 S cm−1). The conductivity remained unchanged when one of the membranes (conductivity = 0.02 S cm−1) was processed at the inlet conditions to a direct propane fuel cell (200 °C and steam mole fraction yH2O =0.86yH2O =0.86). The composite membrane, prepared with glycerol, contained ZrP spheres (100–500 nm) that were smaller than the PTFE pore diameters (1000–2000 nm). The enhanced conductivity may have been caused by a combination of proton transport on the exterior surfaces of the ZrP solid spheres, proton hopping through the bulk of the ZrP, and proton hopping via the OH groups in glycerol.

► We made a Nafion free PEMFC membrane. ► It contained PTFE, zirconium phosphate, and glycerol. ► The conductivity was 40% of the Nafion value. ► It can operate at 200°C.