Boosting the Performance of BiVO₄ Photoanodes by the Simultaneous Introduction of Oxygen Vacancies and Cocatalyst via Photoelectrodeposition

Abstract

Photoelectrochemical (PEC) water splitting is a promising way to convert solar energy into hydrogen energy, but the efficiency is limited by severe charge recombination especially in photoanodes. Herein, to reduce the charge recombination in the bulk phase and at the surface of the BiVO 4 photoanodes, oxygen vacancy introduction and cocatalyst loading were realized simultaneously by one-step photocathode deposition. A unique re-BiVO 4 /FeOOH photoanode was obtained by the photocathodic reduction of BiVO 4 in an electrolyte containing Fe 3+ , where the oxygen vacancies were introduced during the reduction process and the deposition of the FeOOH cocatalyst on the surface was induced by the generated OH − . When used for PEC water oxidation, the obtained re-BiVO 4 /FeOOH photoanode achieved an excellent PEC performance with a photocurrent density of 5.35 mA/cm 2 at 1.23 V versus RHE under AM 1.5G illumination, which was considerably higher than those for the pristine BiVO 4 photoanode (2.88 mA/cm 2 ) and the re-BiVO 4 photoanode obtained by photocathodic reduction without Fe 3+ (4.32 mA/cm 2 ). After further modification with a cobalt silicate (Co-Sil) cocatalyst, the resultant re-BiVO 4 /FeOOH/Co-Sil photoanode exhibited a photocurrent density as high as 6.10 mA/cm 2 at 1.23 V versus RHE and a remarkable applied bias photon-to-current efficiency of 2.25%. The outstanding performance of the re-BiVO 4 /FeOOH/Co-Sil photoanode could be attributed to the coexistence of plenty of oxygen vacancies in BiVO 4 reducing recombination of photogenerated carriers, the FeOOH cocatalyst interlayer as a hole-transport layer, and the outer Co-Sil cocatalyst with a high activity toward oxygen evolution. This work may open a new avenue toward multifunctional modifications of photoanode systems for efficient solar conversion.

Highly Selective Ammonia Oxidation on BiVO4 Photoanodes Co‐catalyzed by Trace Amounts of Copper Ions

“…High‐resolution transmission electron microscopy (HRTEM) images and the corresponding selected area electron diffractions (SAED) pattern of the sample confirmed the high crystallinity (Figure 1c). The estimated lattice spacing of 0.260, 0.308 and 0.310 nm in the SAED pattern were attributed to the (200), (121) and (−121) facets of monoclinic BiVO 4 , which well matched the d‐spacing determined from powder X‐ray diffraction (XRD) analysis (Figure S1a) [9c,12] . Other structural characterizations including the Ultraviolet‐visible diffuse reflectance spectroscopy (UV/Vis DRS) and the energy‐dispersive X‐ray (EDX) elemental mapping of the BiVO 4 photoanodes were also conducted to confirm the successful fabrication of BiVO 4 photoanodes (Figure S1b–f).…”

Engineering Surface Passivation and Hole Transport Layer on Hematite Photoanodes Enabling Robust Photoelectrocatalytic Water Oxidation

“…The fabrication process of the α-Fe 2 O 3 /ZnO/CoTCPP/OECs integrated photoanode based on the previous reports ,− is illustrated in Figure a. First, α-Fe 2 O 3 nanorods were synthesized by the hydrothermal method and subsequent thermal treatment.…”

NiFe-LDH-Decorated Ti-Doped Hematite Photoanode for Enhancing Solar Water-Splitting Efficiency

“…Among them, α-Fe 2 O 3 , in addition to the above-mentioned potential advantages, has a suitable band gap (2.2 eV) to visible-light response, its valence band potential is conducive to water oxygen evolution, and its theoretical photocurrent densities for water oxidation can reach 12.6 mA/cm 2 under AM 1.5G illumination. − Nevertheless, single α-Fe 2 O 3 is susceptible to high charge recombination due to its short hole diffusion lengths and poor kinetics for water oxidation, so a large number of studies aim to ameliorate its PEC performance by modifying it . Morphological controlling, element doping, and heterojunction construction have been acknowledged as being successful tactics for increasing PEC performance. − It is generally known that doping can be done by adding little impurities to a semiconductor to improve its PEC properties. , According to literature reports, doping with different elements, Si, Sn, Ni, Se, and Ti, can significantly enhance the water-splitting efficiency of hematite because they as an electron donor or an electron acceptor substitute a Fe 3+ ion in α-Fe 2 O 3 . Rani et al doped different proportions of Sn 4+ into hematite by hydrothermal methods, and the flat band potential of the photoanode was greatly reduced and showed a better photocurrent density in 4 h .…”