Fabrication and research of bi-functional CuNi₂S₄ nanosheets decorated TiO₂/CuNi₂S₄ heterojunction photoanode for photoelectrochemical water splitting

As a traditional n-type semiconductor, TiO2 has good UV absorption ability and stable physical and chemical properties. However, its wide band gap and low oxygen evolution reaction (OER) activity limit its application in the field of photoelectrochemical (PEC) water splitting. In this work, a type-II TiO2/CuNi2S4 heterojunction photoanode is successfully constructed, which expanded the light absorption range to visible and enhanced the OER activity. Firstly, TiO2 nanotubes (NTs) thin films are prepared on Ti substrates by two-step anodization, and then the bi-functional electrocatalytic material CuNi2S4 is grown on TiO2 NTs in the shape of nanosheets (NSs) in situ by solvothermal method. As a bi-functional electrocatalytic material, CuNi2S4 has good visible light absorption property as well as OER catalytic activity. Compared with TiO2, the IPCE value of TiO2/CuNi2S4 is 2.59% at 635 nm, and that of TiO2 is a mere 0.002%. The separation efficiency and injection efficiency increase from 2.49% and 31.52% to 3.61% and 87.77%, respectively. At 1.23 V vs. RHE, the maximum photocurrent density is 0.26 mA/cm(2), which is 2.6 times than that of TiO2 (0.11 mA/cm(2)), and can be maintained at 0.25 mA/cm(2) for at least 2 h under light illumination. Moreover, a hydrogen production rate of 4.21 mu mol & sdot;cm(-2)& sdot;h(-1) is achieved within 2 h. This work provides a new idea for the application of TiO2 in the field of PEC water splitting and the construction of efficient and stable photoelectronic devices.