A high-performance TiO2 protective layer derived from non-high vacuum technology for a Si-based photocathode to enhance photoelectrochemical water splitting

A TiO2 protective layer can significantly improve the stability of a Si-based photoelectrode. However, employment of a high-vacuum technique in fabricating a high-performance TiO2 protective layer is difficult for a normal laboratory. To solve this problem, in the present work, a composite protective layer of TiO2 and MOF (metal–organic framework) derivatives based on a sol–gel technology is specially designed. Meanwhile, the micropyramid structure has been formed on the Si surface to increase the absorption of incident light, and the catalyst CoP was modified on the surface of the protective layer to improve catalytic activity. Composition of the MOF derivatives could increase band bending of the Si-based photocathode and then enhance the intensity of the built-in electric field, resulting in more photogenerated electrons to migrate to the electrode surface. The TiO2 composite protective layer obtained by the sol–gel method is comparable to the one based on the high vacuum technology. The as-prepared photocathode exhibited excellent PEC hydrogen production performance, including an onset potential of 0.409 V vs. the reversible hydrogen electrode (RHE) and a high photocurrent density of −23.04 mA cm−2 at 0 V vs. RHE under simulated AM 1.5G illumination. Moreover, the obtained photocathode displayed exceptional durability over a period of 144 h.