Vertically Aligned CdO-Decked α-Fe₂O₃ Nanorod Arrays by a Radio Frequency Sputtering Method for Enhanced Photocatalytic Applications

Abstract

Green hydrogen production is one of the most desirable sustainable goals of the United Nations. Thus, for that purpose, we developed hematite (α-Fe 2 O 3 ), an n-type semiconductor, a desirable candidate for photoelectrochemical (PEC) water splitting, enabling hydrogen evolution. High recombination losses, low efficiency, and large-scale production hinder its potential. To address these issues, we have fabricated optimized bare and cadmium oxide (CdO)-decorated hematite thin film nanorod arrays using a throughput radio frequency (RF) sputtering with efficient water splitting behavior. To the best of our knowledge, no work has been done so far on the synthesis of CdO/α-Fe 2 O 3 via RF sputtering for PEC application. Bare α-Fe 2 O 3 samples, with a morphology of vertically aligned nanorods, were fabricated with optimized parameters such as as-deposited 70 nm of Fe, an angle of deposition of 70°, and an annealing temperature of 600 °C, which showed a photocurrent density of 0.38 mA/cm 2 at 1.65 V vs reversible hydrogen electrode (RHE). Characterizations depicted that this unique morphology with high crystallinity directly enhanced the performance of hematite photoanodes. Further, deposition of 30 nm of cadmium (CdO) on the α-Fe 2 O 3 nanorods produced a corn-like morphology with CdO nanoparticles (∼2 nm), resulting in 4-times enhancement of the PEC performance (1.2 mA/cm 2 at 1.65 V vs RHE). CdO acted as a co-catalyst, responsible for satisfactory suppression of recombination and facilitating the hole transfer, directly enhancing the overall photocurrent density. This photoanode showed an extremely stable behavior over a period of 26 h when kept under constant illumination. Furthermore, the CdO-modified photoanode showed a better dye degradation (98% in 40 min) than the bare hematite (60% in 40 min), proving to be an efficient photoanode.

Fabrication of TiVO4 photoelectrode for photoelectrochemical application

“…Hence, if these bimetallic semiconductors can be combined with other novel photoactive materials such as NiO, 16 ZnO, 17 CdO (ref. 18) etc., to construct heterojunctions such as Co 3 O 4 /TiO 2 , 19 Fe 2 O 3 /Au/ TiO 2 , 20 ZnO/Fe 2 O 3 , 21 Fe 2 O 3 /CdO, 22 MoO x /GaP 23 and ZnO/NiO 24 etc. with proper band alignment, they could serve as efficient PEC material as compared to single-phase metal oxide.…”

“…18) etc. , to construct heterojunctions such as Co 3 O 4 /TiO 2 , 19 Fe 2 O 3 /Au/TiO 2 , 20 ZnO/Fe 2 O 3 , 21 Fe 2 O 3 /CdO, 22 MoO x /GaP 23 and ZnO/NiO 24 etc. with proper band alignment, they could serve as efficient PEC material as compared to single-phase metal oxide.…”

Nano multi-layered HfO2/α-Fe2O3 nanocomposite photoelectrodes for photoelectrochemical water splitting

“…To create gaseous hydrogen, the ultimate clean fuel, and oxygen via photocatalytic water splitting, solar energy is turned into chemical energy in so-called PEC cells [ 7 , 8 ]. Since Honda and Fujishima made their discovery in the early 1970s of the photo-assisted electrochemical water oxidation of n-type TiO 2 single-crystal electrodes [ 9 ], it has been used to study different semiconducting materials in order to find a suitable material for this application [ 10 ]including metal oxides, such as TiO 2 [ 11 ],WO 3 [ 12 ], ZnO [ 13 ] and CdO [ 14 ]. However, broad band gaps in these metal oxides mean they can only react to UV light, resulting in inefficient use of solar energy [ 15 ].…”

Synergistic Photoelectrochemical and Photocatalytic Properties of the Cobalt Nanoparticles-Embedded TiVO4 Thin Film

“…However, several drawbacks are more likely to respond to their low efficiency, e.g., band gap structures that cannot straddle some redox potentials to drive overall water splitting reactions. Consequently, charge carriers’ recombination rate is swift, and the slow transport and trapping of charge carriers occur on the surface. − , So, numerous strategies such as doping with other metals, , forming a heterostructure, , and co-catalyst deposition , have been explored to overcome poor metal oxide electrode PEC performance.…”

“…Consequently, charge carriers' recombination rate is swift, and the slow transport and trapping of charge carriers occur on the surface. [7][8][9]13 So, numerous strategies such as doping with other metals, 14,15 forming a heterostructure, 16,17 and cocatalyst deposition 18,19 have been explored to overcome poor metal oxide electrode PEC performance.…”