A New Method to Measure Oxygen Surface Exchange Kinetics On Porous Mixed Conducting Oxides With Simple Determination of Microstructure Parameters.

Oxygen exchange reaction on mixed conducting oxide is a critical reaction for many applications, yet measuring its rate constant remains poorly reliable by standard techniques. Here, a new technique that adapts the conductivity relaxation measurements on porous ceramics is proposed. Using a simple image analysis tool, it is possible to accurately determine the grain size distribution of the porous oxide, which is used in a new relaxation model that integrates relaxation times over that distribution. With such a model, it is possible to fit relaxation transients with the oxygen exchange reaction rate constant kchem as the only fitting parameter. With such rigidity, the output values of kchem are not sensitive to the fitting procedure, which does not require optimization. The model is proven to be applicable to various mixed conducting oxides and to a wide range of microstructures, yielding a remarkably low residual for all the porous ceramics considered. The procedure uses porous ceramics, therefore the derived kinetics are representative of ceramics used in real applications such as fuel cells, sensors, or catalysis.

Critical Binder-to-Powders Coverage Ratio for Faster Graphite/SiOx Electrode Formulation Optimization.

Mastering electrodes' formulations is a complex and tedious task, because for each composition of electroactive material(s) it is necessary to adjust the inactive additives nature and content to optimize battery performance. In this direction, the amount of binder is proposed to be adjusted to the surface developed by all of the powders involved in the composition of the electrode, i.e., the electroactive materials and electronic conductive additives. This concept, introduces here as binder-to-powders coverage ratio, relies upon the micromechanical models developed in the field of polymer-based composite materials. The validity of this new electrode formulation parameter is shown here for two different SiOx /Graphite blends, which differ in the type of graphite, and for blends of two different binders, polyacrylic acid and styrene-butadiene rubber. At the optimal coverage ratio, a satisfactory capacity retention is obtained in full cell with an ethylene carbonate free and fluoroethylene carbonate rich electrolyte.