(Digital Presentation) Plasmonic Enhanced CuBi2O4 Photocathode for Solar Driven Water Splitting
Authors: Kumar Mohit , Subrahmanyam Challapali 
Published: November 2022

Hydrogen is a fuel for sustainable and renewable energy development that emits no carbon dioxide when compared to traditional fossil fuels. Photoelectrochemical (PEC) water splitting is a sustainable method of converting solar energy that falls on earth into useful chemical fuels. However, the sluggish surface reaction kinetics, high cost, and low natural abundance limit the use of photoelectrodes for practical application. It is critical to developing effective and resilient photoelectrodes that provide high efficiency with good stability. Copper based oxides like CuO, Cu2O, CuBi2O4, CuFeO2, and Cu3VO4 are some of the most well-known low-cost materials with apt band gap and band edges for proton reduction reaction. Among them, CuO is one of the most extensively researched photocathodic materials for PEC water splitting owing to its natural abundance and facile synthesis. However, the photocorrosion problem at CuO limits its use in practical application. The conduction band of CuO is contributed by Cu 3d bands which easily get reduced to Cu0 on photoexcited electron diffuse to conduction band. On the other hand, CuBi2O4 is ternary metal oxide which is more resistant and forbids photocorrosion owing to it conduction band contributed by Bi atom orbitals rather than Cu orbitals1.

Metal sulfides like Sb2S3 is good photo-absorber material for solar cells consists of non-toxic and low-cost metal. It has favorable band gap and conduction band and valence band alignment for proton reduction reaction. The type II heterojunction between CuBi2O4 and Sb2S3 can present effective strategy of charge separation and enhanced photoconversion. The plasmon behavior of metal NPs is widely studied in PEC to further improve the photoelectrochemical performance of the photoelectrodes. Plasmonic metal nanoparticles (NPs) absorb light of a threshold wavelength and vibrate emitting out the hot electrons2. Adding Au plasmonic NPs to the photoelectrode might increase the charge carrier concentration, enhance the PEC efficiency, and boost hydrogen production.

The objectives of this study are to investigate fabrication of CuBi2O4/Sb2S3 heterojunction and investigate the dual role of plasmonic Au NPs sandwiched between CuBi2O4/Sb2S3 heterojunction. This heterojunction is developed through three synthesis process: synthesis of CuBi2O4 microrods (MRs) through co-precipitation, Sb2S3 plates via a hybrid chemical bath deposition, and Au NPs via seed-assisted synthesis. XRD, SEM, TEM, and XPS are used to examine the CuBi2O4/Au/Sb2S3, CuBi2O4/Sb2S3, and CuBi2O4/Au heterostructures that were synthesized. At 0 VRHE, the photocurrent of CuBi2O4/Au/Sb2S3 (-3.12 mA.cm-2) was > 200 percent greater than that of pristine CuBi2O4 (-1.45 mA.cm-2), Sb2S3 (-1.02 mA.cm-2), and CuBi2O4/Sb2S3 (-2.15 mA.cm-2). Impedance spectroscopy revealed that CuBi2O4/Au/Sb2S3 has the lowest charge transfer resistance value when compared to the pristines. Stability tests revealed the superior stability of CuBi2O4/Au/Sb2S3 compared to their counterparts3. The increase in photoelectrode PEC activity can be attributed to: (i) effective heterojunction formation for facile charge transfer, (ii) increased light absorption, (iii) incorporation of plasmonic Au NPs increased charge carrier concentration, and (iv) Au NPs also served as a relay for charge transfer between CuBi2O4 and Sb2S3 due to their metallic properties, which increased photoelectrode conductivity. The synergistic effect of fabricated CuBi2O4/Sb2S3 heterojunction and dual role of Au NPs sandwiched resulted in improved PEC conversion and boosted hydrogen evolution. The findings of this study will pave the way for photoelectrodes to be sandwiched between plasmonic NPs through a heterojunction interface that boosts hydrogen production.

References

(1) Li, C.; He, J.; Xiao, Y.; Li, Y.; Delaunay, J. J. Earth-Abundant Cu-Based Metal Oxide Photocathodes for Photoelectrochemical Water Splitting. Energy Environ. Sci.
2020, 13 (10), 3269–3306. https://doi.org/10.1039/d0ee02397c.

(2) Subramanyam, P.; Meena, B.; Biju, V.; Misawa, H.; Challapalli, S. Emerging Materials for Plasmon-Assisted Photoelectrochemical Water Splitting. J. Photochem. Photobiol. C Photochem. Rev.
2022, 51 (November 2021), 100472. https://doi.org/10.1016/j.jphotochemrev.2021.100472.

(3) Kumar, M.; Ghosh, C. C.; Meena, B.; Ma, T.; Subrahmanyam, C. Plasmonic Au Nanoparticle Sandwiched CuBi2O4 /Sb2S3 Photocathode with Multi-Mediated Electron Transfer for Efficient Solar Water Splitting. Sustain. Energy Fuels
2022. https://doi.org/10.1039/D2SE00600F.

Figure 1