In Situ Formation of Oxygen Vacancies Achieving Near‐Complete Charge Separation in Planar BiVO₄ Photoanodes

Abstract

Despite a suitable bandgap of bismuth vanadate (BiVO4) for visible light absorption, most of the photogenerated holes in BiVO4 photoanodes are vanished before reaching the surfaces for oxygen evolution reaction due to the poor charge separation efficiency in the bulk. Herein, a new sulfur oxidation strategy is developed to prepare planar BiVO4 photoanodes with in situ formed oxygen vacancies, which increases the majority charge carrier density and photovoltage, leading to a record charge separation efficiency of 98.2% among the reported BiVO4 photoanodes. Upon loading NiFeOx as an oxygen evolution cocatalyst, a stable photocurrent density of 5.54 mA cm−2 is achieved at 1.23 V versus the reversible hydrogen electrode (RHE) under AM 1.5 G illumination. Remarkably, a dual‐photoanode configuration further enhances the photocurrent density up to 6.24 mA cm−2, achieving an excellent applied bias photon‐to‐current efficiency of 2.76%. This work demonstrates a simple thermal treatment approach to generate oxygen vacancies for the design of efficient planar photoanodes for solar hydrogen production.

Suppressing Water Dissociation via Control of Intrinsic Oxygen Defects for Awakening Solar H2O‐to‐H2O2 Generation

“…[16][17][18] The surface state associated with the intrinsic O vac influences the PEC water splitting activity by kinetically competitive between charge recombination and OER at a Schottky contacted solid/liquid interface, and reasonable controls have been a general strategy to improve PEC efficiency of BiVO 4 . [19][20][21] In recent two years, the surface passivation approaches were found to significantly enhance the H 2 O 2 evolution activity of BiVO 4 , [22,23] making the intrinsic O vac being one of the key considerations for the possibilities of low H 2 O 2 evolution selectivity of the synthetic BiVO 4 . Although there are numerous studies to elucidate the roles of O vac on charge transfer kinetics (e.g., like trap and donor), the dynamics of dissociation of water molecules on the O vac existing BiVO 4 surface is rarely considered.…”

In situ characterizations of photoelectrochemical cells for solar fuels and chemicals

“…11 More recently, a record charge separation efficiency of 98.2% was reported for planar BiVO 4 photoanodes. 39 These are encouraging results and demonstrate that metal-oxides have the potential to be engineered into efficient devices for solar H 2 production. Nevertheless, the bandgap of BiVO 4 is still too high for commercial viability.…”

Stable Cocatalyst‐Free BiVO4 Photoanodes with Passivated Surface States for Photocorrosion Inhibition

“…The O 1s spectrum (Figure 2 l) can be divided into three fitting peaks, lattice oxygen (O L ), hydroxyl groups bonded to the metal cations in the oxygen deficient region (O V ), and chemisorbed oxygen species from the water molecules (O C ). [16] A negative shift (ca. 0.6 eV) is detected in O L .…”

“…3 nm). This suggests that the amorphous layer favors to passivate the surface states, especially after 3 h. [16] The XRD patterns (Figure 2 f) display the crystalline BiVO 4 phase (JCPDS No. 83-1699), whilst no any other phases (e.g.…”

“…[14] On the other hand, synthesizing high-quality BiVO 4 nanostructures is useful for enhancing the hole transfer to the surface for OER. [15][16][17] Previous researches have aimed for intentionally inducing defect sites (e.g. oxygen vacancies and disordered layer) on these structures for tuning the charge transport properties.…”