3D Hierarchical Nanorod@Nanobowl Array Photoanode with a Tunable Light‐Trapping Cutoff and Bottom‐Selective Field Enhancement for Efficient Solar Water Splitting

Abstract

oxide (FTO) hexagonal nanocone and nanospikes, [7,8] and also Cui and Xiao et al. have deposited nanoporous Mo-doped bismuth vanadate (Mo:BiVO 4 ) on an engineered cone-shaped nanostructure to form inverse nanocone array BiVO 4based photoanodes. [9,10] These works deposited a thin photoactive material on a 3D conductive substrate constructed by various complicated methods to shorten charge transport distance and enhance light absorption. Scientific analysis with experiments and modeling showed that these 3D nanophotonic structures can "trap" the incident light to the near-surface region and extend the absorption region to 800 nm and even above.However, the maximum absorption wavelength, below which the corresponding photon energy can be absorbed and converted into electron-hole pairs by photoelectrode, is dependent on the bandgap of the specific photoactive materials. [11,12] Therefore the enhanced light trapping beyond the maximum absorption wavelength can be detrimental in a series-connected photocathode and photoanode tandem system or a PEC-photovoltaic (PEC-PV) tandem device, since it will only greatly weaken or even eliminate the light available to the narrow-bandgap material and thus bring down the solar-to-hydrogen (STH) efficiency. Some works attempted to distribute the solar band to advantage by splitting standard AM 1.5 irradiation into two light beams with an additional splitter, but this means a higher cost and more complex equipment hindering practical application. [8,9] At the same time, Constructing 3D nanophotonic structures is regarded as an effective means to realize both efficient light absorption and efficient charge separation. However, most of the 3D structures reported so far enhance light trapping beyond the absorption onset wavelength, and thus greatly attentuate or even completely block the long-wavelength light, which could otherwise be efficiently absorbed by narrow-bandgap materials in a Z-scheme or tandem device. In addition, constructing a 3D conductive substrate often involves complex processes causing increased cost and upscaling problems. To overcome these shortcomings, a novel 3D hematite nanorod@nanobowl array nanophotonic structure is designed and fabricated by a low-cost method. This unique structure can enhance light absorption with tunable cutoffs and rationally concentrate photons right above the bowl bottom, enabling efficient charge separation. By loading NiFeO x as a cocatalyst, a high photocurrent density of 3.41 ± 0.2 mA cm −2 at 1.23 V versus reversible hydrogen electrode (RHE) can be obtained, which is 2.35 times that with a planar structure in otherwise the same system. Water SplittingThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.

Photoelectrochemical technology for solar fuel generation, from single photoelectrodes to unassisted cells: a review

“…The light-harvesting efficiency, as well as carriers' transport and separation efficiency, were enhanced and a photocurrent density of ~ 3.1 mA/cm 2 (1.23 versus reversible hydrogen electrode, AM 1.5G) was generated for water oxidation. Furthermore, a Fe 2 O 3 photoanode with a 3D hierarchical nano-bowl array structure was designed for photoelectrochemical water splitting (Tang et al 2019). Under this unique structure, the light harvest would be enhanced with tunable cutoffs and rationally concentrate photons right above the bowl bottom to enable more efficient charge separation in the branched nano bowl substrates.…”

Engineering the heterogeneous interfaces of inverse opals to boost charge transfer for efficient solar water splitting

“…These can promote photo-induced charge separation and transportation [17][18][19][20]. Some excellent nanostructures can be found in the literature with considerable improvement for PEC performance, such as CdS nanorod@SnO 2 nanobowl [21], Fe 2 O 3 nanorod@nanobowl [22], 3D g-C 3 N 4 /Ni(OH) 2 [23], WO 3 / BiVO 4 /Co-Pi inverse opal [24], and fluorine-doped tin oxide (FTO)/FTO-nanocrystal/TiO 2 inverse opal [25]. However, heterogeneous interfaces in the composite photocatalysts can lead to inappropriate energy band arrangements that result in serious charge recombination because of the undesired barriers.…”

Self‐Assembled Urchin‐Like CuWO4/WO3 Heterojunction Nanoarrays as Photoanodes for Photoelectrochemical Water Splitting

“…[4,5] Hence, exploring efficient photoanode materials toward oxygen evolution reaction (OER) are essential to for PEC water splitting. The single metal oxides, such as ZnO, [6] TiO 2, [7,8] α-Fe 2 O 3 [9,10] and WO 3, [11,12] have been extensively investigated as photoanodes. However, their measured performance towards PEC water oxidation is still far from satisfaction as a result of the inherent defects.…”