Enhanced photoactivity towards bismuth vanadate water splitting through tantalum doping: An experimental and density functional theory study

Abstract

The activation of hole trap states in bismuth vanadate (BiVO₄) is considered an effective strategy to enhance the photoelectrochemical (PEC) water-splitting activity. Herein, we propose a theoretical and experimental study of tantalum (Ta) doping to BiVO₄ leading to the introduction of hole trap states for the enhanced PEC activity. The doping of Ta is found to alter the structural and chemical surroundings via displacement of vanadium (V) atoms that cause distortions in the lattice via the formation of hole trap states. A significant enhancement of photocurrent to ∼4.2 mA cm^-2 was recorded attributing to the effective charge separation of efficiency of ∼96.7 %. Furthermore, the doping of Ta in the BiVO₄ lattice offers improved charge transport in bulk and decreased charge transfer resistance at the electrolyte interface. The Ta-doped BiVO₄ displays the effective production of hydrogen (H₂) and oxygen (O₂) under AM 1.5 G illumination with a faradaic efficiency of 90 %. Moreover, the density functional theory (DFT) study confirms the decrease in optical band gap and the activation of hole trap states below the conduction band (CB) with a contribution of Ta towards both valence and CB that increases the charge separation and majority charge carrier density, respectively. The findings of this work propose that the displacement of V sites with Ta atoms in BiVO₄ photoanodes is an efficient approach for enhanced PEC activity.

Keywords: BiVO(4); Catalysis; Density functional theory; Hole trap states; Tantalum.