Polyphosphoric Acid Proton Conductors and Their Application, to Fuel Cell Electrolytes

Abstract

This study aims at a solidification of fuel cell electrolyte using polyphosphoric acids. When the electrolyte of phosphoric acid cells was replaced by metaphosphoric acid, the density of limiting current was greatly lowered without an essential change 'in the polarization. This marked performance drop was attributed to the high viscosity of polyphosphoric acids. Phosphoric acid was solidified when copolymerized with silicic acid, becoming a solid proton conductor which could be used at 200°C for a fuel cell electrolyte. The all-solid cell installed with this solid electrolyte sustained a load of 400 mA/cm² with approximately the same anode polarization as for the phosphoric acid cells, but with much greater potential drops of the cathode. The cell performance has been discussed in relation to the effective reaction area of the electrode-electrolyte interface.