Effect of graphite on the electrochemical properties of ballmilled RuO2

High energy ballmilling of mixtures of RuO2 and graphite was performed as a function of the milling time and the weight fraction of the components. Cyclic voltammetry as a function of the sweep rates was performed in 1 M H2SO4 at room temperature to determine the total specific charge and the most easily accessible charge. It is shown that the specific charge of RuO2-graphite mixtures reaches a maximum for milling time comprised between 60 and 120 min. This corresponds to a RuO2 utilization efficiency of 8.3%. This is eight times larger than the utilization efficiency of crystalline RuO2 and two times larger than that of nanocrystalline RuO2 (crystalline RuO2 milled by itself during 30 h). For longer milling time (>5 h), partial reduction of RuO2 occurs, and the total specific charge decreases. The ratio of the most easily accessible charge to the total specific charge increases to a value close to 1 as the weight ratio of graphite in the mixture increases from 10 to 50 wt %. (C) 2004 The Electrochemical Society.