Understanding electron transfer processes and oxygen reduction electrocatalysis in nanocrystalline Cu-MOF-74

•Nanocrystalline Cu-MOF-74 (crystal size ≅ 40 nm) was evaluated as electrode material.•Efficient electron transport through the Cu-MOF-74 structure was verified.•Cu-MOF-74 electrocatalyzes oxygen reduction to water on a microporous surface.•Dissolved oxygen is captured by unsaturated Cu centers exposed at the MOF micropores.•Reduction of captured oxygen is mediated by Cu2+ electro-reduction.