## 3 Results and Discussion
### Photoelectrochemical Characterization
The trend in photocurrent densities for the different deposition times was also maintained when the electrodes were probed by CA at \(-0.2\) V vs. SCE (Figure S15), although the steady-state photocurrent values measured were lower. Interestingly, the samples prepared at longer photoelectrodeposition times (\(>\)30 s) showed rapidly decreasing photocurrents attributable to charge recombination processes, most likely determined by the presence of large amounts of Pt HEC on the electrode surface. Method 2, which differs from Method 1 in the absence of the light bias, was also employed for the preparation of NiO photocathodes (hereafter named NiO-A \(\mid\)**P1**\(\mid\)Pt-**2**). Previous studies that employed Method 2 as a platinization procedure usually considered long deposition times (\(>\)300 s) [27; 28]. Attempts at preparing NiO-A \(\mid\)**P1**\(\mid\)Pt-**2** electrodes with such deposition times were, however, unsuccessful, as negligible photocurrent densities, close to those of the blank sample, as well as considerable dark currents, ascribed to direct electrocatalysis by Pt, were measured. Shorter deposition times, similar to those employed in Method 1, were thus considered. These electrodes systematically performed worse than those obtained with Method 1, leading to maximum photocurrent densities of \(-10\)\(\mu\)A\(\cdot\)cm\({}^{-2}\) at 10 s and \(-12\)\(\mu\)A\(\cdot\)cm\({}^{-2}\) at 20 s as measured by LSV under chopped irradiation (Figure 4B). This suggests that the coupling of both light and electrochemical potential is important to favor effective Pt deposition onto sensitized NiO electrodes. A similar trend was observed also in the CA measurements (Figure S16 of the Supplementary Materials). The best results obtained using both Methods 1 and 2 at short deposition times clearly evidence the necessity of having a small amount of catalytic Pt metal on the sensitized NiO surface. Large amounts of catalyst may indeed play the role of recombination centers, thus decreasing the possibility of profitably converting photogenerated electrons into molecular hydrogen [25; 29]. In this respect, we envisioned that the application of an inherently fast procedure such as cyclic voltammetry might well comply with this important requirement. As a matter of fact, the potentiodynamic deposition methods (Methods 3-5) turned out to be effective for the platinization of sensitized NiO electrodes, with performances that depended on the presence and duration of the light bias. Figure 4C shows the LSV traces obtained under chopped irradiation of electrodes prepared according to Methods 3-5 (hereafter named NiO-A \(\mid\)**P1**\(\mid\)Pt-**3**, NiO-A \(\mid\)**P1**\(\mid\)Pt-**4**, and NiO-A \(\mid\)**P1**\(\mid\)Pt-**5**, respectively), whereas in Figure S17, the corresponding CA traces recorded at \(-0.2\) V vs. SCE are reported. Maximum photocurrent densities in the order of \(-29\), \(-27\), and \(-40\)\(\mu\)A\(\cdot\)cm\({}^{-2}\) were measured for the NiO-A \(\mid\)**P1**\(\mid\)Pt-**3**, NiO-A \(\mid\)**P1**\(\mid\)Pt-**4**, and NiO-A \(\mid\)**P1**\(\mid\)Pt-**5** electrodes, respectively. According to these data, Method 5, which combines a CV scan and a short illumination, provides the most active photocathodes. Although the SEM/EDS analysis suggests a similar distribution of the Pt HEC onto the sensitized NiO surface, the beneficial effect of including light irradiation under both potentiostatic and potentiodynamic conditions is clearly apparent. The resulting improvement most likely stems from subtle structural arrangements as well as NiO/dye/catalyst interactions that might differ when the **P1** dye takes an active part (as in Methods 1, 3, and 5) or does not (as in Methods 2 and 4) in the reduction of the Pt(IV) electrolyte and the nucleation of Pt. The NiO electrodes obtained via the best deposition procedures among the potentiostatic and potentiodynamic methods (viz.