Structure-dependent electrocatalytic properties of Cu₂O nanocrystals for oxygen reduction reaction

Cu₂O nanocrystals with different morphologies are synthesized via a reductive solution route by controlling the reaction time and using different capping agents. Introducing poly(ethylene glycol) (PEG) leads to nearly monodispersed Cu₂O nanocubes with 40 nm size and dominant {100} crystal planes. With prolonged reaction time, the nanocubes are truncated and transformed into sphere-like nanocrystals with more {111} planes exposed. In the presence of poly(vinyl pyrrolidone) (PVP), porous Cu₂O nanocrystals with both {100} and {111} planes present are produced. The structure-dependent electrocatalytic activity of Cu₂O nanocrystals toward oxygen reduction reaction (ORR) has been studied in alkaline electrolyte. The electrocatalytic activity measured on Cu₂O {100} is higher than that on Cu₂O {111}. In addition, the Cu₂O nanocubes with dominant {100} crystal planes show the highest four-electron selectivity (n = 3.7) and lowest peroxide yield (15%) during the ORR. Kinetics analysis indicates that the ORR mechanism on Cu₂O nanocrystals is controlled simultaneously by charge transfer and intermediate migration. The Cu ₂O nanocrystals also show better methanol tolerance and durability for ORR than the commercial Pt/C materials.