A ZnO/ZnFe2O4 uniform core-shell heterojunction with a tubular structure modified by NiOOH for efficient photoelectrochemical water splitting.

It is known that heterojunction photoelectrodes can improve light absorption and accelerate the separation of photogenerated carriers in the field of photoelectrochemical (PEC) water splitting. However, the key to efficient photoelectrochemical performance is to build heterojunctions with a narrow band gap semiconductor loaded on a wide band gap semiconductor uniformly and densely. Herein, a ZnO/ZnFe2O4 uniform core-shell heterojunction photoelectrode is prepared by a simple ion etching method. Moreover, the chemical reaction process and mechanism are discussed in detail. The ZnO/ZnFe2O4 photoelectrode shows a higher photocurrent density (0.29 mA cm-2 at 1.23 V vs. RHE) compared with that of ZnO (0.17 mA cm-2 at 1.23 V vs. RHE). Furthermore, the PEC performance of ZnO/ZnFe2O4 is optimized by depositing NiOOH; the photocurrent density of ZnO/ZnFe2O4/NiOOH is 0.48 mA cm-2 at 1.23 V vs. RHE. The remarkable PEC performance of ZnO/ZnFe2O4/NiOOH benefits from the following important factors: (i) the uniformity and nanotube structure of the ZnO/ZnFe2O4 heterojunction; (ii) the excellent light harvesting ability; and (iii) the reduced photogenerated electron-hole pair recombination rate. This work provides new insights into designing heterojunction systems for efficient photoelectrochemical water splitting.