Ceramic conductors for electrochemical cell applications: new perspectives in materials and synthesis

A great number of compounds with electronic and ionic conductivity and new synthesis routes are being explored for electrochemical applications. In this work, selected examples are described. (a) CaO–TiO2–Fe2O3 materials prepared by combustion synthesis are low cost products with interesting mixed conduction, the electrical behavior of which indicates the existence of a transition, where the grain interior electrical contribution is the dominant effect from 7% mol iron content. (b) Mixed electronic–ionic conducting SmCoO3 perovskites with dispersed Pt particles were prepared by combustion synthesis. The as-prepared powders showed very small metallic Pt particles and exhibited acceptable catalytic performance in methanol oxidation. (c) Materials belonging to the Ti1−xRuxO2 system, 0≤x≤1 (mol), were synthesized by a polymeric sol-gel route. Two types of electrical behavior were detected in sintered materials of this system: semiconductor and metallic. A wide semiconductor/metal transition was observed. The metal/electrical percolation could be located at a composition of x=0.26. (d) On the other hand, amorphous nanopore materials with protonic conduction obtained by appropriate synthesis can be used as electrolytes in PEMFCs. SiO2 nanopore ceramic membranes were prepared using a colloidal sol-gel technique. The chips were mesoporous with an average pore size of 3.5 nm.