Engineering Nanostructure–Interface of Photoanode Materials Toward Photoelectrochemical Water Oxidation

Abstract

In practical applications, solar energy is usually converted to other forms of energy, such as electric energy, [9][10][11] chemical energy, [12,13] thermal energy, [14,15] so as to facilitate further transportation and storage. Among them, photoelectrochemical (PEC) reactions from water to hydrogen, CO 2 to C2+ products, and N 2 to NH 3 in the aqueous-based environment have been considered to be quite promising solar-chemical energy conversion pathways. [16][17][18][19] Unlike the traditional water electrolyzing system, the most ideal PEC reaction system can be selfdriven by illumination without external bias. Utilizing the electron-hole carriers generated from the semiconductor photoelectrode, redox reactions take place separately on the photocathode and photoanode. However, as the water oxidation reaction involves a complex four-proton coupled multi-electron process (2H 2 O + 4h + → O 2 + 4H + , E o = 1.23 V vs reversible hydrogen electrode (RHE)), it makes the water oxidation reaction the rate-control step in the watersplitting reaction. [20] Therefore, developing high-performance photo anodes is of great fundamental importance and interest.At the present stage, TiO 2 is the most studied and applied semiconductor photoelectrocatalyst, due to its outstanding chemical stability. [21][22][23] However, as a wide bandgap semiconductor (anatase TiO 2 : 3.2eV, rutile TiO 2 : 3.0 eV), TiO 2 can only respond to the ultraviolet light. Meanwhile, as an intrinsic semiconductor, the bulk/surficial carrier recombination of TiO 2 greatly hinders its practical application. [24][25][26][27] In that case, some narrow bandgap semiconductors are also applied as the photoanode materials, such as Ta 3 N 5 (bandgap 2.1 eV), [28,29] BiVO 4 (bandgap 2.4 eV), and α-Fe 2 O 3 (bandgap 2.1 eV). [30][31][32] However, many of these narrow bandgap materials suffer from poor chemical stability and sluggish interfacial charge injection. [33][34][35] As intrinsic semiconductor materials, both wide and narrow bandgap semiconductor photoanode materials are suffering from the poor bulk-phase carrier separation, intense surficial e − /h + trapping recombination, and sluggish electrode/electrolyte carrier injection kinetics. [36][37][38][39] Fortunately, with the continuous investment of researchers, a series of modification methods have been established and the PEC water oxidation performance of semiconductor photoanode materials has been significantly improved. [32,[40][41][42][43][44] Among various strategies, nanostructure-interface engineering is widely regarded as an effective method to improve the PEC water oxidation performance: [40,41] the light-harvesting performance can be enhanced by the widened optical Photoelectrochemical (PEC) water oxidation based on semiconductor materials plays an important role in the production of clean fuel and value-added chemicals. Nanostructure-interface engineering has proven to be an effective way to construct highly efficient PEC water oxidation photoanodes with good light capture, carrier transport, and ...

Recent Progress on Semiconductor Heterojunction‐Based Photoanodes for Photoelectrochemical Water Splitting

“…The larger the specific surface area is, the larger is the contact region between the photoanode and electrolyte, which would result in better PEC performance. [ 73 ] Yang and co‐workers [ 74 ] grew nanoporous BiVO 4 coated onto SnO 2 nanorods, which increased the contact area between BiVO 4 /SnO 2 and electrolyte and was beneficial to the improvement of the performance of the photolysis of water and the rate of hydrogen production. Second, the construction of micro–nanostructures improves the light capture capabilities of photoanodes.…”

“…Second, the construction of micro–nanostructures improves the light capture capabilities of photoanodes. [ 73 ] Compared with conventional bulk planar structures, nanorods, nanosheets, nanobowl arrays, and other structured photoanodes exhibit better light refraction capabilities, which lengthens light traveling, extends the interaction between the light and the photoanode, and improves light harvesting efficiency. Tian et al [ 75 ] grew In 2 S 3 nanosheets on WO 3 nanowalls to enhance the light refraction and contact area with electrolytes compared to WO 3 nanowalls, which caused WO 3 /In 2 S 3 heterojunctions to possess PEC potential.…”

Host/Guest Nanostructured Photoanodes Integrated with Targeted Enhancement Strategies for Photoelectrochemical Water Splitting

“…[16][17][18] Much effort has been made to develop advanced techniques for fabricating novel nanostructures as semiconductor photoanodes. [19][20][21] Nanostructures can usually enhance solar energy harvesting, reduce diffusion length of the charge carriers, and increase the contact area with the electrolyte, thus improving the STH conversion efficiency of one PEC cell. Various nanostructures such as 1D nanorods (NRs) [22,23] and nanowires (NWs), [24] 2D nanosheets (NSs), [25,26] 3D inverse opals (IOs) [27,28] have been reported for efficient PEC applications.…”

Improving Photoelectrochemical Activity of ZnO/TiO2 Core–Shell Nanostructure through Ag Nanoparticle Integration

“…Besides a relatively large band gap for ZnO and TiO 2 , one of the main factors is the low carrier transfer efficiency due to fast recombination of the photogenerated electrons and holes. To overcome this obstacle, strategies such as heterostructural construction have been employed [21][22][23][24][25]. In the application of PEC water splitting, nanostructured semiconductor photoelectrode possesses a large surface-to-volume ratio (SVR), thus reducing the migration distance of photo-excited carriers and facilitating their transfer to surface.…”