Enhanced Photoelectrochemical Performance of BiFeO₃ Doped with Calcium: Doping Induced Heterojunction Through Phase Separation

Here we report on considerable enhancement in photoelectrochemical, PEC, performance of BiFeO₃ induced by 20% Ca doping. We demonstrate that although doping is commonly carried out in low concentration of the dopants, order of few percentages, what we can call heavy doping, 20%, used in this work proven to be advantageous and serve as an efficient charge separation mechanism. At such high Ca percentage, phase separation takes place and other phases, mainly Fe₂O₃ (α/γ Fe₂O₃), are introduced into the material forming heterostructured photocatalyst with improved properties. This is carried out without resolving to the use of expensive rare earth cocatalyst. Polycrystalline BFO and 20% Ca doped photoelectrodes were synthesized by doctor blading. XRD showed the formation of Fe₂O₃ (α/γ Fe₂O₃) phase along with the BFO one. Particle size decreased significantly upon Ca doping promoting concomitant enhancement of ferromagnetism. The photocurrent density at 0.75 V showed fivefold increase upon 20% Ca doping. The enhancement in the photocurrent, charge carriers density and the reaction rate at the surface of the electrode deduced from electrochemical impedance spectroscopy recommend that Ca doping at such high percentage provide a mechanism for the separation of photogenerated charges. Elemental mapping suggested the non-perfect correlation between Bi and Fe as expected for a phase separated system. Band alignment of the different phases existing in the system could imply the formation of nanojunctions formed between BFO and α/γ Fe₂O₃ leading to increase in carrier lifetime. It is low cost approach to improve the performance of the multiferriocs photoelectrode towards the production of clean solar energy.