Piezoelectric polarization-induced photogenerated carriers transfer coupled with active electron transport Z-scheme heterojunction synergistic optimization of BiFeO3/CdS composite photocatalysts for hydrogen production

Photocatalytic hydrogen production technology is an effective way to convert solar energy into chemical energy with the advantage of cleanliness and non-pollution, whereas efficient, stable and inexpensive photocatalysts are the top priority. The efficiency of separation, transportation and utilisation of photogenerated carriers is fundamental in limiting the rate of photocatalytic hydrogen production reactions. In this study, Z-scheme heterostructures with active electron transport properties are constructed with multiferroic BiFeO3 and favorable visible light-responsive CdS nanosheets. The active electron transport system is constructed to promote carrier separation and transport, which presents a novel strategy for the enhancement of photocatalytic hydrogen production reaction activity. The heterostructure of the composites not only optimises the light absorption capacity and band structure, but also reduces the interfacial resistance and photogenerated carrier recombination. The combination of BiFeO3 particles and ultrathin CdS not only suppresses the agglomeration of CdS nanosheets, but also assists in enhancing the specific surface area of the reaction system. More importantly, the nanosheet structure of CdS as the reducing phase facilitates proton adsorption and hydrogen desorption. The piezoelectric effect possessed by BiFeO3 and CdS leads to the triggering of spontaneous polarisation moments in response to external forces. The introduction of polarisation factors can enhance the driving force of charge separation in the bulk phase thereby forming an internal electric field. Photogenerated electron-hole pairs during photocatalysis migrate to the surfaces of different polar domains under the influence of the internal electric field. The piezoelectric polarisation process exhibits significantly enhanced properties for the charge redistribution in the bulk phase of the catalyst as well as inducing the efficient separation of photogenerated carriers with further migration at the interface through the Z-mechanism heterojunction. The hydrogen evolution rate of the composite containing 20 wt% CdS reaches 3.58 mmol center dot g- 1 center dot h- 1 under photo-piezoelectric coupling conditions, which is 116.64 fold higher than that of the pristine BiFeO3 under visible light irradiation. This study will provide an important theoretical basis and practical guidance on the application of multifield coupling to modulate charge transfer as well as inducing interfacial catalytic reactions.