Given CO₂’s role as a major greenhouse gas, one of the greatest challenges of the 21^st century will be the reduction of CO₂ emissions with the current average of CO₂ abundance in the atmosphere around 405 ppm compared with pre-industrial revolution levels of around 280 ppm.¹ Given this problem, research into developing and utilising renewable and sustainable energies has become a priority for the scientific community. With a wide irradiance spectrum (100 nm – 1 mm), an energy density of ~1360 W/m² in the upper atmosphere, and ~1000 W/m² as it reaches sea level, solar radiation is an unmatched potential source of renewable energy, much greater than current worldwide demands.² To utilise this energy, highly active photovoltaic devices are needed, with metal oxide semiconductor materials being ideal candidates.³

1D nanostructured titanium dioxide (TiO₂) materials are an ideal candidate to meeting the criteria needed for developing future photovoltaic devices with efficient photocatalytic performance given their stability, low toxicity, and advantageous photocatalytic properties.⁴ TiO₂ nanorod arrays grown on transparent conductive oxides (TCOs) are employed as photocatalysts for a wide range of reactions with a focus on the Oxygen Evolution Reaction (OER) given their high specific surface areas and alignment resulting in direct charge transport pathways.^{5, 6} One of the challenges of direct growth of these nanostructures on TCOs is the texture and surface roughness of the substrate which can have unfavourable effects such as undesirable alignment, disruption of growth length and lowered nanorod area density.⁷ By simply etching a substrate surface with Inductively Coupled Plasma (ICP) etching these surface properties can be easily altered to allow for more favourable direct growth conditions.⁸

This work will look at the impact of the FTO surface texture, grain size and surface roughness on hydrothermally grown TiO₂ nanorod layers by comparing etched and non-etched FTO substrates. How these surface properties affect density, alignment, morphology, and phase structure of the TiO₂ nanorods will be shown as well as these properties importance in relation to photocatalytic activity for the Oxygen Evolution Reaction.

References

[1] Lindsey, R. Climate Change: Atmospheric Carbon Dioxide. https://www.climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide (accessed Feb 7, 2019).

[2] Vieira, L. E. A.; Kopp, G.; Lean, J. L., A new, lower value of total solar irradiance: Evidence and climate significance. Geophysical research letters 2011, 38 (1).

[3] Li, J.; Wu, N., Semiconductor-based photocatalysts and photoelectrochemical cells for solar fuel generation: a review. Catalysis Science & Technology 2015, 5 (3), 1360-1384.

[4] Fattakhova-Rohlfing, D.; Zaleska, A.; Bein, T., Three-Dimensional Titanium Dioxide Nanomaterials. Chemical reviews 2014, 114 (19), 9487-9558.

[5] Liu, B.; Yang, J.; Wang, J.; Zhao, X.; Nakata, K., High sub-band gap response of TiO2 nanorod arrays for visible photoelectrochemical water oxidation. Applied Surface Science 2019, 465, 192-200.

[6] Cho, I. S.; Chen, Z.; Forman, A. J.; Kim, D. R.; Rao, P. M.; Jaramillo, T. F.; Zheng, X., Branched TiO2 Nanorods for Photoelectrochemical Hydrogen Production. Nano letters 2011, 11 (11), 4978-4984.

[7] Kim, H.; Yang, B. L., Effect of seed layers on TiO2 nanorod growth on FTO for solar hydrogen generation. International Journal of Hydrogen Energy 2015, 40 (17), 5807-5814.

[8] Zhang, L.; Verma, A.; Xing, H.; Jena, D., Inductively-coupled-plasma reactive ion etching of single-crystal β-Ga2O3. Japanese Journal of Applied Physics 2017, 56 (3), 30304.