Controlled O reduction at a mixed-valent (II,I) CuS core.

Inspection of Oxygen Reduction Reactions (ORRs) using a mixed-valent Cu2S complex as a pre-catalyst revealed a tuneable H2O2vs. H2O production under mild conditions by controlling the amount of sacrificial reducer. The fully reduced bisCuI state is the main active species in solution, with fast kinetics. This new catalytic system is robust for H2O2 production with several cycles achieved and opens up perspectives for integration into devices.