Optimization of BiVO4 coatings for high yield photoelectrochemical production of reactive chlorine species

Abstract

Photoelectrochemical (PEC) synthesis of valuable chemicals, such as hydrogen and oxidants, is widely studied as a potential alternative to replace conventional synthesis processes with high carbon footprint. In the present study two different approaches were used to improve photoelectrochemical activity of BiVO4 coatings, i.e. doping with molybdenum and heterostructuring with BiOCl. Crystalline structure, chemical composition and morphology of the coatings were characterized using X-ray diffraction, energy-dispersive spectroscopy and scanning electron microscopy techniques. Performance of the photoelectrodes was tested in the solutions of Na2SO4 and NaCl. PEC activity was found to increase in the sequence BiVO4 < Mo_BiVO4 < Mo_BiVO4/BiOCl and the enhancement was much more pronounced in chloride medium. Mo doping was found to double incident photon to current conversion efficiency (from 5% to 10%) as well as Faradaic efficiency of photoinduced generation of reactive chlorine species (RCS) (from an average of 36% to 78%). Formation of hypochlorite and chlorite (ClO− and ClO2−) was determined experimentally. Construction of heterojunction between Mo_BiVO4 and BiOCl promoted separation of photogenerated electrons and holes and led to significant enhancement of photocurrent. Moreover, presence of BiOCl layer was found to catalyze photooxidation of ClO− to ClO2−. Findings of the study demonstrate the potential of BiVO4-based coatings for photoelectrochemical production of RCS via saline water splitting.