## 3 Results and Discussion
### Photoelectrochemical Properties of TiO\({}_{2}\)/FTO and Au/TiO\({}_{2}\)/FTO Photoelectrodes  
Figure 5a shows voltammograms of the samples under study. The titanium dioxide electrode is electrochemically stable over the entire potential range. The deposition of gold promotes an increase in the current density; however, peaks of electrochemical transformations of unknown origin at 0.4 V appear on the voltammogram. The probable explanation of the observed phenomenon may be supported by the electrochemical gold oxidation in basic solutions to the corresponding oxide. This effect was mentioned for bare gold in solutions of sodium hydroxide [31] or sodium hydrocarbonate [32]. This peak would have been saved if gold particles were deposited on the substrate, for example, on nickel hydroxide [31]. Perhaps, in solutions of sodium sulfide, gold oxidation by hydroxide ions  
Figure 4: Optical density spectra of TiO\({}_{2}\)/FTO and Au/TiO\({}_{2}\)/FTO films. may also be occurred. The ox-red potential of gold oxidation is known to be ca. 0.5 V; however, this position may be changed depending on hydroxide concentration and/or sweep rates. Figure 5b shows on-off curves for the studied photoelectrodes. It can be seen that in the first three cycles of switching the lighting on and off, a slight decrease in the short-circuit current density occurs, and, over the next six cycles, this value does not change. Thus, the obtained materials are distinguished by high stability of electrodes in time, which is important when considering aspects of the practical application of the obtained photoelectrodes. In a stable mode of operation, a porous TiO\({}_{2}\) film is characterized by a photocurrent density of about 0.2 mA/cm\({}^{2}\). The deposition of plasmonic gold nanoparticles by the LCLD method has a significant effect on the photocurrent density, increasing it approximately 10-fold. As shown in Table 1, gold deposition can improve other photovoltaic characteristics, for example, open circuit potential, which increased from 13 mV to 27 mV. The maximum value of the open circuit potential is logarithmically related to the short circuit current density [33]. An increase in \(I_{sc}\) by 9.2 times leads to an increase in \(V_{oc}\) by a factor of 2.2, in accordance with the logarithmic dependence. The filling factor for both electrodes is the same and amounts to 28%. The efficiency of converting the energy of light radiation into electricity \(\eta\) increases when gold is deposited on the surface of titanium dioxide. It is likely that the deposition of gold makes it possible to improve the separation of charge carriers in space, which favors the photocatalytic and photovoltaic properties of the samples under study. For a more detailed consideration of the effect arising from the deposition of gold on titanium dioxide, studies were carried out using impedance spectroscopy. The obtained data in Nyquist coordinates are shown in Figure 6. It can be seen that the TiO\({}_{2}\)/FTO hodograph radius significantly decreases when the sample surface is modified with gold. Thus, the resistance in the system is significantly reduced, which may be associated with an increase in the photovoltaic characteristics \(I_{sc}\) and \(\eta\). \begin{table}
\begin{tabular}{c c c c c} \hline
**Photoelectrode** & \(J_{sc}\)**, mA/cm\({}^{2}\)** & \(V_{oc}\)**, mV** & \(FF_{z}\) \% & \(\eta_{z}\) \% \\ \hline TiO\({}_{2}\)/FTO & 0.294 & 13 & 28 & 0.019 \\ \hline Au/TiO\({}_{2}\)/FTO & 2.711 & 27 & 28 & 0.374 \\ \hline \end{tabular}
\end{table} 
Table 1: Photovoltaic characteristics of the photoelectrodes under study. Figure 5: Cyclic voltammogram of the TiO\({}_{2}\)/FTO and Au/TiO\({}_{2}\)/FTO samples (**a**); time variation of the short-circuit current density of the TiO\({}_{2}\)/FTO and Au/TiO\({}_{2}\)/FTO samples (**b**).