Enhancing the Protonic Conductivity of Tin Pyrophosphates by Increasing Phosphate Content

摘要

Indium-doped tin pyrophosphate materials were synthesized with varying metal to phosphate ratios to assess the influence of the excess amorphous polyphosphate phase on conductivity. Total conductivity at 250°C was found to increase with increasing P:M ratio, with a maximum conductivity of 10~(-1.8) Scm~(-1) in dry N_2 and 10~(-0.8) Scm~(-1) in humidified N_2. These results combined with supporting spectroscopy, suggest that a grain-boundary polyphosphate phase is required to achieve high conductivity at low-intermediate temperatures. The conductivity of the excess phosphorous content materials was stable in both dry and humidified environments at 250°C. The use of this material as a promising fuel cell electrolyte was demonstrated with a maximum power density of 11 mWcm~(-2) obtained for the highest P:M ratio material at 300°C without humidification. This value is an order of magnitude lower than what has been reported previously in the literature. However the conductivity of the electrolyte in the operating fuel cell was 0.075 Scm~(-1) and the poor performance is attributable to cathodic overpotentials.