Stoichiometric and non-stoichiometric tungsten doping effect in bismuth vanadate based photoactive material for photoelectrochemical water splitting

Role of Alkali Metal in BiVO4 Crystal Structure for Enhancing Charge Separation and Diffusion Length for Photoelectrochemical Water Splitting

“…The effect of the co-catalyst on the photocurrent measurement is shown in Figure S1e. The catalyst Fe/Ni enhanced the hole storage effect at the interface, whereas Co–Pi collected the holes at the interface, which also participated in the water oxidation reaction. , The K:BiVO 4 and Na:BiVO 4 photoanodes (Figure b) exhibited a PCD of 4 ± 0.2 and 5.55 ± 0.3 mA·cm –2 at 1.23 V RHE , respectively, in the presence of a hole scavenger (Na 2 SO 3 ), where the electron–hole recombination is almost negligible …”

“…An increasing demand for H 2 for various applications motivated researchers around the world to explore sustainable production methods. , The photoelectrochemical (PEC) route is one of the long-term green approaches for producing green H 2 by water splitting using solar irradiation and electrical energy. , The PEC cell consists of a semiconducting anode/cathode immersed in an aqueous electrolyte, leading to water oxidation/reduction through charge separation in the bulk of the electrode material by light absorption at the photoelectrode surface. , However, the photoanodes suffer from issues such as limited light absorption spectrum, slow electron–hole pair transfer to the semiconductor/electrolyte interface, and chemical and electrochemical instability. , Monoclinic scheelite bismuth vanadate (BiVO 4 ) is an attractive photoanode material due to its defect tolerant nature, light absorption capability up to ≥520 nm, suitable direct band gap ( E g = 2.4–2.5 eV) ideal for oxygen evolution reaction (OER), and ability to demonstrate a fairly high photocurrent density (PCD) at low bias at pH ∼ 7 . But the BiVO 4 photoanode also suffers from many drawbacks such as substantial electron–hole recombination due to a shorter diffusion length for electrons (∼10 nm) and holes (∼100 nm) leading to sluggish water oxidation kinetics, , limited absorption, and a relatively wider band gap . Also, the position of the conduction band edge is below the H 2 reduction potential, requiring additional potential to provide a favorable condition for water splitting .…”

“…Also, the position of the conduction band edge is below the H 2 reduction potential, requiring additional potential to provide a favorable condition for water splitting . Several attempts have been made to improve the performance of BiVO 4 through doping, junction formation, nanostructuring, and also by adding an electron transfer layer and a hole transfer layer . Among these strategies, employing a p–n homojunction is a useful technique for promoting band alignment, charge separation, and transfer due to a built-in internal electric field at the p–n junction. − Doping with transition metals (IIIA to VIIA group elements) has been proven to be one of the practical approaches for increasing OER by enhancing diffusion length, charge carrier separation/transport, and light absorption by reducing the band gap. − Wang et al have reported that the HER and OER can be promoted by doping to enhance active sites, lower overpotential, and improve durability.…”

Photoelectrochemical Solar Water Splitting: The Role of the Carbon Nanomaterials in Bismuth Vanadate Composite Photoanodes toward Efficient Charge Separation and Transport

“…FTO glass substrate (active area, 1 × 1 cm 2 ) was dipped in the precursor solution for 5 s, vacuum-dried at 50 °C for 10 min, and heat-treated at 300 °C in air for 5 min for preparing pristine BiVO 4 film. The aforementioned procedure was repeated to coat three layers and finally calcined at 450 °C in air for 2 h . Various nanomaterials (MWCNT, rGO, and GCN) were incorporated into BiVO 4 samples as given below.…”

“…FTO glass substrate (active area, 1 × 1 cm 2 ) was dipped in the precursor solution for 5 s, vacuum-dried at 50 °C for 10 min, and heat-treated at 300 °C in air for 5 min for preparing pristine BiVO 4 film. The aforementioned procedure was repeated to coat three layers and finally calcined at 450 °C in air for 2 h. 25 Various nanomaterials (MWCNT, rGO, and GCN) were incorporated into BiVO 4 samples as given below. Carbon nanomaterials (4.0 wt %) were dispersed in 1 mL of 2 M nitric acid for 5 min using horn sonicator (Branson, Modelsfx 20:0.25) and added to 4 mL of BiVO 4 precursor solution, and the BiVO 4 /CNT, BiVO 4 /rGO, and BiVO 4 /GCN samples were prepared by dip coating as given above.…”