Elucidating the role of surface states of BiVO4 with Mo doping and a CoOOH co-catalyst for photoelectrochemical water splitting

Nanoscale Assembly of BiVO4/CdS/CoOx Core–Shell Heterojunction for Enhanced Photoelectrochemical Water Splitting

“…Figure 4g shows the high-resolution XPS spectrum in the Co region, remarking the presence of two main Co species (Co 2+ and Co 3+ ) and one satellite: the peaks corresponding to Co 3+ signals were found at 779.85 and 794.85 eV, while those related to Co 2+ were at 782.25 and 797.05 eV. The presence of both Co 2+ and Co 3+ ions (and the absence of nitrogen in the XPS survey spectrum) confirms the successful deposition of a Co oxide (we call it CoO x , but it might contain Co 2 O 3 , Co 3 O 4 , or a mixture of them) at the surface of the photoanodes [9,44]. Furthermore, the O 1s spectrum of BiVO 4 /CdS/CoO x in Figure 4h shows three peaks.…”

“…Figure 2a shows the XRD patterns of bare BiVO 4 photoanode with characteristic diffraction peaks, which correspond to the (110), ( 121), (040), ( 200), (002), (211), (051), (132), (042), ( 202) and (161) reflections of monoclinic scheelite BiVO 4 [9] (JCPDS 14-0688). The CdS layer is indexed to the hexagonal structure [44] (JCPDS 41-1049) with corresponding crystal planes of (002), ( 101), ( 102), (100) and (103).…”

“…In Figure 4b, the dominant peak at 516.7 eV can be ascribed to V 2p 3/2 . The binding energy peak of 529.85 eV corresponds to the lattice oxygen in BiVO 4 , while the peak at 531.45 eV can be assigned to the non-lattice or adsorbed oxygen (Figure 4c), indicating adsorbed oxygen species, e.g., hydroxyl groups or water, on the surface of BiVO 4 photoanodes [9]. The peaks positioned at binding energies of 405.3 and 412.1 eV in Cd 3d spectrum (Figure 4d) can be indexed to Cd 3d 5/2 and Cd 3d 3/2 , respectively.…”

“…To verify the elemental composition and chemical state of the photoanode, X-ray photoelectron spectroscopy (XPS) analysis was conducted. Figure 4a shows the high-resolution (HR) region of Bi 4f, where the two main peaks with binding energies of 159.25 and 164.45 eV can be attributed to Bi 4f7/2 and Bi 4f5/2, respectively [9]. In Figure 4b, the dominant peak at 516.7 eV can be ascribed to V 2p3/2.…”

“…On the other hand, the main drawback that significantly limits their practical utilization for a large-scale industrial production of H 2 is their wide bandgap (e.g., 3.0-3.2 eV for TiO 2 , 2.7 eV for WO 3 , and 3.1-3.3 eV for ZnO), which is translated into poor absorption of the solar spectrum, hence the low PEC-WS efficiency [6,7]. In contrast, bismuth vanadate (BiVO 4 ) has a significantly narrower bandgap energy, around 2.4-2.5 eV, and simultaneously shows a good stability and enables low-cost production [8,9]. The application of BiVO 4 for solar water oxidation was first reported by Kudo et al in 1998 [10].…”