Highly ordered ZnO/ZnFe2O4 inverse opals with binder-free heterojunction interfaces for high-performance photoelectrochemical water splitting

Highly ordered heteronanostructures with binder-free interfaces are the key factors in developing high-performance photoanodes. Here, we design and fabricate three-dimensional ordered macroporous ZnO/ZnFe2O4 inverse opals with binder-free heterojunction interfaces that improve the separation of photogenerated charge carriers. The well-defined ZnO/ZnFe2O4 inverse opal displays a high photoconversion efficiency of 0.81% at 0.38 V versus the RHE without any co-catalyst assistance, which is over 6 times higher than that of the pristine ZnO sample (0.13% at 0.65 V vs. the RHE). Furthermore, the photoanode is quite stable even after 10 h of continuous illumination with a slight photocurrent decay of 4.9% (88.0% loss for the pristine ZnO). The high performances of the ZnO/ZnFe2O4 inverse opals can be attributed to the improved interfacial charge carrier separation based on electrochemical analysis and first-principles calculations. This work may provide more insights into the design of highly efficient photoanodes for photoelectrochemical applications.