Post-Treatment Techniques to Enhanced the Light Absorption and Charge Transport of BiVO4 for Water Splitting in Photoelectrochemical Cell

U. Prasad, J. Prakash, A.M. Kannan, B. Azeredo
Arizona State University,
United States

Keywords: water splitting, photoelectrochemical cell, BiVO4, post treatment

Summary:

Monoclinic BiVO4 is a promising photoactive material for the hydrogen production by water splitting in photoelectrochemical cell (PEC). However, wide band gap (~2.4-2.5 eV) limits its solar to hydrogen conversion efficiency. In the present work, the band gap of pristine BiVO4 has been tuned using post-treatment techniques to enhance water splitting performance. Thin film electrodes of BiVO4 has been prepared by dip coating method on FTO (Fluorine-doped Tin Oxide) substrate. Coating of single and multiple layers of BiVO4 were carried out on FTO and subsequently their water splitting performance evaluated. It was observed that with increase of BiVO4 layers up to 3 layers, there were increase in PCD (photocurrent density) (Fig.1). Subsequently with increasing BiVO4 layer decreases PCD. It was observed that effective separation of charge carries may be reason for such different layer BiVO4 performance. BiVO4 film was annealed at 350°C for 2h in N2 environment. This induced N2 doping and generation of oxygen vacancies helped in reducing bandgap, increases light absorption, and charge transport by increasing the majority carrier density and mobility. Also, charge recombination process has been delayed by enhancing electron charge separation. The nitrogen treatment has shown 35-40% improvement in water splitting performance of BiVO4 film electrode (Fig.2).