Reduction of Oxygen on Dispersed Nanocrystalline CoS2

The electrocatalytic properties of nanocrystalline CoS2 have been investigated for the oxygen reduction reaction (ORR) in 0.1 M HClO4. CoS2 with pyrite structure was prepared by hydrothermal synthesis and attached to a glassy carbon electrode from solution with a mixture of carbon and Nafion. The prepared CoS2 electrode layers showed high activity toward the ORR and very good stability under oxygen reducing conditions. Selectivity of the ORR toward H2O2 was determined by rotating (ring) disk electrode measurements, and relatively high selectivity was obtained with up to 80% H2O2 formation around 0.4 V (vs Ag/AgCl), but this dropped to zero for potentials below 0.0 V. The amount of H2O2 produced between 0.6 and 0.0 V was dependent on the quality of the CoS2 dispersion within the electrode layer, and decreasing CoS2 particle size resulted in. significant improvement in the ORR electrocatalytic activity, both by increasing the turnover frequency and through decreasing the selectivity toward H2O2 production.