Boosting the photocathode performances of protected Cu2O inverse opals using photonic-crystal heterostructures

Cuprous oxide (Cu2O) is a highly efficient p-type semiconductor photocatalytic material with the capability for visible light absorption. In this work, three-dimensional Cu2O inverse opals with different diameters were prepared using the electrochemical deposition method. The photocathode performances were enhanced by adjusting the wavelength of photonic band gap, being co-modified by Au and Ag nanoparticles, applying the protective layers, and fabricating a photonic-crystal heterostructure with another p-type semiconductor. The slow-light effect leads a 23.9 % increase in photocurrent density. The co-modification of Au and Ag nanoparticles achieves a 77 % average increase in photocurrent density compared with pure Cu2O inverse opals. Conformal protective layers, consisting of ZnO and Al2O3 and deposited using atomic layer deposition, prevent the photocorrosion of the Cu2O photocathode while preserving its photocatalytic activity. After one hour of illumination, the photo-generated current density of protected Cu2O inverse opals is nearly three times higher than that of their uncoated counterparts. By fabricating Ag-doped ZnO with p-type characteristics and combining it with Cu2O into a heterostructure, the saturated photocurrent density of the Ag-doped ZnO/Cu2O heterostructure reaches −3.78 mA/cm2, which is almost 3.2 times higher than that of pristine Cu2O inverse opal at −0.12 V vs RHE.