Amorphous Cu_(2-δ)O as Passivation Layer for Ultra Long Stability of Copper Oxide Nanowires in Photoelectrochemical Environments

Core-shell CuO-Cu_2O nanowires with a surface amorphous Cu2-δO layer leads to high stability photocathodes for use in photoelectrochemical splitting of water. The nanowires are synthesized via carbothermal reduction of CuO nanowires at 300°C during which a 2–3 nm conformal and amorphous Cu_(2-δ)O layer is formed on the nanowire surface. This Cu_(2-δ)O layer enhances photocurrent and improves photocorrosion stability of the nanowires. While catalyst-free, pristine CuO nanowires show a photocurrent density is 0.50 mA/cm^2 and a stability of 53% after 3.4 hours of testing at −0.50 V under AM1.5 G conditions; the catalyst-free, carbothermally reduced nanowires achieve a photocurrent density of 0.75 mA/cm^2 and an improved stability of 96% under identical test conditions. The mechanism of enhanced photocurrent and its stability is discussed in the context of extensive pre and post test nanowire characterization.