TiO2 nanofiber photoelectrochemical cells loaded with sub-12 nm AuNPs: Size dependent performance evaluation
Macdonald, Thomas J
Shapter, Joseph George
Parkin, Ivan P
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Incorporation of gold nanoparticles (AuNPs) into titanium dioxide (TiO2) photoelectrodes has been used traditionally to increase the performance of photoelectrochemical cells (PECs) through their tailored optical properties. In contrast to larger AuNPs, previous studies have suggested that smaller AuNPs are the most catalytic or effective at increasing the photovoltaic (PV) performance of TiO2 photoelectrodes based on PECs. Despite this, AuNPs are often only compared between sizes of 12–300 nm in diameter due to the most common synthesis, the Turkevich method, being best controlled in this region. However, the optimum radius for citrate-capped AuNPs sized between 5 and 12 nm, and their influence on the PV performances has not yet been investigated. In addition to using AuNPs in the photoelectrodes, replacing traditional TiO2 NPs with one-dimensional nanofibers (NFs) is a promising strategy to enhance the PV efficiency of the PECs due their capability to provide a direct pathway for charge transport. Herein, we exploit the advantages of two different nanostructured materials, TiO2 NFs and sub-12 nm AuNPs (5, 8, 10, and 12 nm), and fabricate composite based photoelectrodes to conduct a size dependent performance evaluation. The PECs assembled with 8 nm AuNPs showed ∼20% improvement in the average power conversion efficiency compared to the control PECs without AuNPs. The highest performing PEC achieved a power conversion efficiency of 8%, which to the best of our knowledge, is among the highest reported for scattering layers based on pure anatase TiO2 NFs. On the basis of our comprehensive investigations, we attribute this enhanced device performance using 8 nm AuNPs in the TiO2 NF photoelectrodes to the improved spectral absorption, decreased series resistance, and an increase in electron transport and injection rate leading to an increase in current density and fill factor.
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