A BiVO₄Photoanode with a VO_xLayer Bearing Oxygen Vacancies Offers Improved Charge Transfer and Oxygen Evolution Kinetics in Photoelectrochemical Water Splitting

Abstract

Sluggish oxygen evolution kinetics are one of the key limitations of bismuth vanadate (BiVO 4 ) photoanodes for efficient photoelectrochemical (PEC) water splitting. To address this issue, we report a vanadium oxide (VO x ) with enriched oxygen vacancies conformally grown on BiVO 4 photoanodes by a simple photoassisted electrodeposition process. The optimized BiVO 4 /VO x photoanode exhibits a photocurrent density of 6.29 mA cm À 2 at 1.23 V versus the reversible hydrogen electrode under AM 1.5 G illumination, which is ca. 385 % as high as that of its pristine counterpart. A high charge-transfer efficiency of 96 % is achieved and stable PEC water splitting is realized, with a photocurrent retention rate of 88.3 % upon 40 h of testing. The excellent PEC performance is attributed to the presence of oxygen vacancies in VO x that forms undercoordinated sites, which strengthen the adsorption of water molecules onto the active sites and promote charge transfer during the oxygen evolution reaction. This work demonstrates the potential of vanadium-based catalysts for PEC water oxidation.

Engineering BiVO4 and Oxygen Evolution Cocatalyst Interfaces with Rapid Hole Extraction for Photoelectrochemical Water Splitting

“…Bismuth vanadate (BiVO 4 ) has been recognized as a promising photoanode material for PEC water splitting because of its narrow bandgap (2.4–2.5 eV) and deep valence band edge, enabling PEC water oxidation under visible light illumination. − However, BiVO 4 photoanodes suffer from serious charge recombination and sluggish water oxidation kinetics due to the poor charge transport characteristics and short hole-diffusion length (<70 nm), thus leaving plenty of room to improve the PEC performance toward its theoretical maximum (7.5 mA cm –2 ) under AM 1.5 G illumination. − In the past decades, heteroatom doping, − structural tuning, , crystal facet engineering, , heterojunction construction, , defect engineering, − and loading of oxygen evolution cocatalysts (OECs) − have been regarded as effective strategies for overcoming these drawbacks and improving the PEC water oxidation activity and stability of BiVO 4 photoanodes. It should be mentioned that oxygen evolution reaction (OER) is a complicated four-electron transfer process, and decorating BiVO 4 surfaces with proper OECs is of great importance to suppress surface charge recombination. − However, modification of the BiVO 4 surfaces with some highly active OECs cannot always achieve a high PEC performance, which is attributed to the small driving force at the OEC/BiVO 4 interfaces that cannot promptly extract all photogenerated holes from BiVO 4 for OER. , Therefore, it is highly desirable to explore a proper approach to suppress charge recombination at the OEC/BiVO 4 interfaces for efficient PEC water splitting.…”

Tandem cells for unbiased photoelectrochemical water splitting

“…The BiVO 4 is one of the most widely studied photoanodes for water oxidation due to its relatively narrow band gap (2.4 eV), low cost, and good chemical stability. 122,123 Kudo et al 124 and Li and co-workers 125,126 conducted an in-depth study of powder-based BiVO 4 photocatalysts in terms of performance and fundamental understanding, providing design principles for the investigation of BiVO 4 . The BiVO 4 photoelectrode, exhibits a higher photocurrent than that of Fe 2 O 3 , TiO 2 , and WO 3 , and so on, while showing a positive onset potential (0.2 V RHE ) which was comparable to that of TiO 2 (0.1 V RHE ).…”

Enhancing the photoelectrochemical activity of monoclinic BiVO4by discretizing oxygen vacancies: insights from DFT calculations

“…5–7 Among semiconductors, monoclinic bismuth vanadate (BiVO 4 ) has become one of the most promising candidate materials for PEC water splitting owing to its suitable band gap energy, superior hole mobility, and low fabrication cost. 8–13 However, the STH conversion efficiency of BiVO 4 is still far below the theoretical value, which is mainly hindered by fast nonradiative electron–hole recombination. 14,15 Defects are inevitable in semiconductors, which can introduce sub-band gap states within the bandgap, and strongly affect the photogenerated carrier dynamics performance.…”