Controlled O 2 reduction at a mixed-valent (II,I) Cu 2 S core.

Inspection of Oxygen Reduction Reactions (ORRs) using a mixed-valent Cu2S complex as a pre-catalyst revealed a tuneable H(2)O(2)vs.H2O production under mild conditions by controlling the amount of sacrificial reducer. The fully reduced bisCu(I)state is the main active species in solution, with fast kinetics. This new catalytic system is robust for H(2)O(2)production with several cycles achieved and opens up perspectives for integration into devices.