Recent Advances in Visible-Light-Driven Photoelectrochemical Water Splitting: Catalyst Nanostructures and Reaction Systems

Abstract

Photoelectrochemical (PEC) water splitting using solar energy has attracted great attention for generation of renewable hydrogen with less carbon footprint, while there are enormous challenges that still remain for improving solar energy water splitting efficiency, due to limited light harvesting, energy loss associated to fast recombination of photogenerated charge carriers, as well as electrode degradation. This overview focuses on the recent development about catalyst nanomaterials and nanostructures in different PEC water splitting systems. As photoanode, Au nanoparticle-decorated TiO₂ nanowire electrodes exhibited enhanced photoactivity in both the UV and the visible regions due to surface plasmon resonance of Au and showed the largest photocurrent generation of up to 710 nm. Pt/CdS/CGSe electrodes were developed as photocathode. With the role of p-n heterojunction, the photoelectrode showed high stability and evolved hydrogen continuously for more than 10 days. Further, in the Z-scheme system (Bi₂S₃/TNA as photoanode and Pt/SiPVC as photocathode at the same time), a self-bias (open-circuit voltage V _oc = 0.766 V) was formed between two photoelectrodes, which could facilitate photogenerated charge transfers and enhance the photoelectrochemical performance, and which might provide new hints for PEC water splitting. Meanwhile, the existing problems and prospective solutions have also been reviewed.

Keywords: Heterojuction; Hybrid systems; Nanostructures; Photoelectrochemical water splitting; Reaction system.

Fig. 1

The schematic setup of PEC water splitting system

Fig. 2

Semiconductors coated on substrate as photoanode for PEC water splitting [15]

Fig. 3

SEM images of titanium dioxide arrays [29, 34]

Fig. 4

The overlapping in band gaps between two different photocatalysts and the electron-trap mechanism

Fig. 5

Schematic interfacial electron transfer between TiO₂ and Bi₂WO₆ [47]

Fig. 6

The diagram of BiVO₄/WO₃ heterojunction and electron transport process [58]

Fig. 7

FeOOH as photoanode for photoelectrochemical water splitting [60]

Fig. 8

The scheme of the nanostructure of the CdS/TiO₂ nanoarrays and charge-transfer mechanism [68]

Fig. 9

Semiconductors coated on substrates as photocathode for PEC water splitting [15]

Fig. 10

SEM image of a p–n Cu₂O homojunction [78]

Fig. 11

Schematic representation of the electrode structure of the surface-protected Cu₂O electrode [80]

Fig. 12

EDX mapping of CdS/CuGaSe₂ sample with chemical bath deposition for 1 min [18]

Fig. 13

n-type and p-type semiconductors coated on substrates as photoanode and photocathode, respectively, for PEC water splitting (Z-scheme) [15]

Fig. 14

Reaction and band model in photovoltaic cell using p-type CaFe₂O₄ and n-type TiO₂ semiconductor electrodes [83]

Fig. 15

The energy-level diagram of the self-biasing PEC cell assembled with Bi₂S₃/TNA photoanode and Pt/SiPVC photocathode under short-circuit situation [19]