Composite heterojunction of BiFeO3 and CdS: A photocathode for promoting efficient decomposition of water using piezoelectric photoelectrocatalysis

BiFeO3 has excellent potential as a narrow band gap semiconductor and piezoelectric material for photoelectrochemical decomposition of water (PEC) applications. However, because of its susceptibility to impurities and oxygen vacancy defects during preparation and its high complexation rate of photogenerated carriers, relevant applications are greatly limited. In this paper, BiFeO3/CdS heterojunction films were prepared on FTO conductive glass by a very simple and feasible sol-gel and chemical bath method to improve the efficiency of the photoelectrochemical decomposition of water. It was shown based on a series of PEC tests. The photocurrent density of the pure BiFeO3 thin film photocathode reached −85 μA/cm2 after giving ultrasonic stress conditions. Furthermore, the BiFeO3/CdS heterojunction photocathode achieved a photocurrent density of about −230 μA/cm2 at 0 V vs. RHE under the synergistic effect of piezoelectric polarization and the built-in electric field built in the heterostructure. In summary, semiconductor modification approaches using the construction of suitable heterojunction structures can effectively promote the separation and transfer of carriers between interfaces. The use of piezoelectric polarization and the search for appropriate energy level-matched semiconductors to construct heterojunctions can synergistically improve the efficiency of piezoelectric photocatalysis. The composite of BiFeO3 and CdS to form type II heterojunction effectively improves the photoelectrocatalytic performance of BiFeO3 under piezoelectric effect. [Display omitted] •Both BiFeO3 and CdS films are in the form of nanosheets and the fabrication process is simple and can be done in the laboratory.•Compared with the enhancement of piezoelectric effect under ultrasonic condition, the internal electric field formed by heterojunction can further increase the concentration of photogenerated carrier, thus improving its separation efficiency.