Engineering Ba₂Bi₂O₆ Double Perovskite with La³⁺ for High Current Density Visible Light Photoelectrochemical Hydrogen...

A Lanthanum ion (La³⁺) incorporation strategy is implemented to modify Ba₂Bi₂O₆-based double perovskite photoelectrodes. X-ray diffraction (XRD) characterization shows that highly crystalline Ba₂La_0.4Bi_1.6O₆ double perovskites with the space group I2/m are successfully prepared. UV-vis absorption spectra and the Tauc-plot reveal an optical band gap E_g ≈1.57 ± 0.01 eV. A thickness dependence of the photoelectrodes photoelectrochemical (PEC) performance shows that the submicron (≈1 µm) 4-times spin-coated thin film photoelectrode displays strong p-type conductivity, which delivers an encouraging photocurrent density of 0.88 mA cm^-2 at 0.25 V_RHE under AM 1.5G illumination. 10-times coated and 20-times coated medium thick (125.8-197 µm) photoelectrodes that exhibit moderate p-type conductivity, show further enhanced photocurrent densities of 1.5 mA cm^-2 at 0 V_RHE. In contrast, charge recombination centers existing in a standard thick pellet (≈500 µm) Ba₂La_0.4Bi_1.6O₆ photoelectrode can quench photo-generated charge carriers and greatly undermine PEC activities. The approach to doping at the Bi(III) sites contrasts with earlier efforts that focus on doping at the Bi(V) sites and thus paves the way for further tailoring a family of novel promising photocathode materials for efficient solar-water conversion devices.