Epitaxial growth of cactus-like heterojunction with perfect interface for efficient photoelectrochemical water splitting

Co3O4 is an ideal p-type material for photoelectrochemical (PEC) hydrogen evolution, while serious electron-hole recombination restrict its further improvement of the PEC activity. The construction of traditional heterojunction can effectively solve this problem. However, the PEC water splitting efficiency is still tough to be satisfactory due to the inevitable generation of heterojunction interface defects. Herein, we fabricate the epitaxial growth of FeS nanowires at an angle of 60 degrees on the Co3O4 nanosheets via electrostatic adsorption and form S-O bonds at the interface. The cactus-like heterojunction overcomes the problem of the large interfacial defects of heterojunction and improves the separation efficiency of photogenerated carriers. As a result, a photocurrent density of Co3O4/ FeS is 9.953 mA cm-2 at 0 VRHE for 22 h without any obvious decay, which is approximately 10 times higher than that for pristine Co3O4 (0.966 mA cm-2 at 0 VRHE), greatly improving the efficiency of PEC water splitting and stability. It is better than most Co3O4-based photocathodes without cocatalyst and even comparable with the advanced Co3O4-based photocathodes. This work significantly addresses the issue of interfacial defects in heterojunction and provides constructive guidance for the construction of perfect interfacial heterojunction in the future.