Piezophotodegradation and piezophotoelectrochemical water splitting of hydrothermally grown BiFeO₃ films with various morphologies

This paper reports the use of the hydrothermal method in the fabrication of pure BiFeO₃ (BFO) films with various morphologies [microparticle (BFO_MP), microplate (BFO_MPL), and microsheet (BFO_MS)] on fluorine-doped tin oxide substrates and their applications in piezophotodegradation and piezophotoelectrochemical water splitting. These samples exhibited p-type characteristics, band gaps of approximately 2.1 eV, and favorable crystal. Piezoresponse force microscopy revealed that the piezoelectric coefficients of BFO_MP, BFO_MPL, and BFO_MS were 13.0, 18.6, and 15.3 pm V⁻¹, respectively. The associated piezotronic and piezophototronic characteristics of the samples were verified through facile current–voltage measurement, which revealed that BFO_MPL outperformed BFO_MP and BFO_MS. Electrochemical and photoluminescence (PL) analyses demonstrated that BFO_MPL possessed the highest electrochemical surface area per-unit mass (22.6 mF cm⁻² mg⁻¹) and the weakest PL emission. The combination of these characteristics and the favorable energy band positions under stress of BFO_MPL contributed to its excellent piezophotocatalytic performance, with a piezophotodegradation rate constant of approximately 19.8 × 10^–3 min⁻¹ for methylene blue solutions, a piezophotoelectrochemical current density of approximately − 0.83 mA·cm⁻² at −0.6 V (vs. Ag/AgCl) and a maximum piezo-induced applied bias photon-to-current conversion efficiency of 0.54% at −0.51 V. Based on the enhanced piezoelectricity, which can effectively enhance the separation of photogenerated electron-hole pairs, thus improving photocatalyst performance. BFO_MPL also exhibited good reusability and versatility toward degrading different organic pollutants. The results indicate that our samples are promising for application in environmental sustainability.