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In this work, the synthesis of a Mo(sub)/Zn/Sn/Cu metallic stack through electrodeposition is achieved by using an ethyleneglycol-based solution designed to deposit Sn onto a Mo/Zn substrate. The displacement reaction with zinc is minimized through the formation of complexes with diethanolamine. A correlation between the electrochemical behavior of Sn(II) species and the reactivity of zinc upon immersion in the tin plating bath is shown. Morphological and compositional characterization is carried out on the Zn/Sn/Cu stack at the different synthesis steps. Reactive annealing is carried out to convert the metallic precursor into CZTS with a minor presence of secondary phases. The resulting CZTS/CdS/Pt photoelectrode shows a photocurrent density of À 5.73 mA cm À 2 at 0 V vs RHE under 1 sun (AM 1.5 G). This study demonstrates how the chemistry of the plating bath is crucial for the deposition of thin films onto reactive substrates, reducing the technological gap with vacuum-based deposition methods.

The integration of cobalt borate OER catalysts with electrodeposited BiVO4-based photoanodes through a simple drop casting technique was shown to provide an improvement of the photoelectrochemical performance of electrodes under simulated solar light. Catalysts were obtained by chemical precipitation mediated by NaBH4 at room temperature. Scanning electron microscopy (SEM) investigation of precipitates showed a hierarchical structure with globular features covered in nanometric thin sheets providing a large active area, whereas X-ray diffraction (XRD) and Raman spectroscopy highlighted their amorphous structure. The photoelectrochemical behavior of samples was investigated by linear scan voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) techniques. The amount of particles loaded onto BiVO4 absorbers was optimized by variation of the drop cast volume. The enhancement of photocurrent generation by Co-Bi-decorated electrodes with respect to bare BiVO4 was observed with an increase from 1.83 to 3.65 mA/cm2 at 1.23 V vs RHE under AM 1.5 simulated solar light, corresponding to a charge transfer efficiency of 84.6%. The calculated maximum applied bias photon-to-current efficiency (ABPE) value for optimized samples was 1.5% at 0.5 V applied bias. Under constant illumination at 1.23 V vs RHE, a depletion of photoanode performances was observed within an hour, likely due to the detachment of the catalyst from the electrode surface.

Iron oxyhydroxide (FeOOH) was implemented as a low-cost, stable, and earth-abundant catalyst on hydrogenated titania nanorods array (H-TiO 2 /FeOOH), for photoelectrochemical water splitting applications. The hydrogenation treatment enhanced the maximum photocurrent density delivered by the titania-based photoanode (from 0.65 mA cm −2 to 1 mA cm −2 at +1.23 V vs RHE) while the exploitation of FeOOH resulted in a significant improvement in the photoelectrochemical activity at low bias. The optimized photoelectrode showed ∼0.6 mA cm −2 at +0.4 V vs RHE, with a saturation current density of 1.05 mA cm −2 . Insights on the role of FeOOH were revealed by electrochemical impedance and photoluminescence measurements, suggesting a reduction of the charge transfer resistance at the electrolyte interface and a lower frequency of recombination events. The H-TiO 2 /FeOOH photoelectrode showed a maximum applied bias photon-to-current efficiency (ABPE) of 0.68% with a 0.3 V bias, while for the bare TiO 2 nanorods array the maximum value of 0.4% was found at a bias of 0.4 V. A stable photocurrent was measured in 1 M NaOH solution through a 5 h test at 1.23 V vs RHE, under illumination (1 sun), suggesting the compatibility of FeOOH in highly alkaline solutions.