Abstract
Currently, hydrogen generation via photocatalytic water splitting using semiconductors is regarded as a simple environmental solution to energy challenges. This paper discusses the effects of the doping of noble metals, Ir (3.0 at.%) and Ni (1.5–4.5 at.%), on the structure, morphology, optical properties, and photoelectrochemical performance of sol-gel-produced SnO2 thin films. The incorporation of Ir and Ni influences the position of the peaks and the lattice characteristics of the tetragonal polycrystalline SnO2 films. The films have a homogeneous, compact, and crack-free nanoparticulate morphology. As the doping level is increased, the grain size shrinks, and the films have a high proclivity for forming Sn–OH bonds. The optical bandgap of the un-doped film is 3.5 eV, which fluctuates depending on the doping elements and their ratios to 2.7 eV for the 3.0% Ni-doped SnO2:Ir Photoelectrochemical (PEC) electrode. This electrode produces the highest photocurrent density (Jph = 46.38 mA/cm2) and PEC hydrogen production rate (52.22 mmol h−1cm−2 at −1V), with an Incident-Photon-to-Current Efficiency (IPCE% )of 17.43% at 307 nm. The applied bias photon-to-current efficiency (ABPE) of this electrode is 1.038% at −0.839 V, with an offset of 0.391% at 0 V and 307 nm. These are the highest reported values for SnO2-based PEC catalysts. The electrolyte type influences the Jph values of photoelectrodes in the order Jph(HCl) > Jph(NaOH) > Jph(Na2SO4). After 12 runs of reusability at −1 V, the optimized photoelectrode shows high stability and retains about 94.95% of its initial PEC performance, with a corrosion rate of 5.46 nm/year. This research provides a novel doping technique for the development of a highly active SnO2-based photoelectrocatalyst for solar light-driven hydrogen fuel generation.
Highlights
Introduction published maps and institutional affilPhotoelectrochemical water splitting (PEC-WS) and the hydrogen generation process using unlimited solar energy have attracted increased attention worldwide
Demonstrating abundance, facile preparation, chemical stability in a wide range of pH values [1], and environmental compatibility [5], SnO2 is a semiconductor material that inherits a direct bandgap (Eg ) of 3.6 eV with a high exciton binding energy at room temperature (RT) [2]; its electron mobility is in the order of 240 cm2 V−1 S−1 [6], and it has high transparency in the visible range, low resistance, and high reflectivity for infrared iations
The crystal growth in the (2 0 0) and (2 1 1) directions means that all films are polycrystalline and composed of randomly oriented crystals
Summary
The source of Sn was SnCl2 ·2H2 O, MW~225.63, from Merck, whereas the source of Ir element was IrCl3 ·H2 O, MW~298.58 g/mol from Sigma. 0.325 M solutions of SnO2 and 3.0% Ir-doped SnO2 (SnO2 :Ir) were synthesized by dissolving the required amounts of SnCl2 ·2H2 O and IrCl3 ·H2 O/SnCl2 ·2H2 O, respectively, in 10 mL ethanol for each. These two solutions were stirred at 60 ◦ C for 3 h. To obtain SnO2 :Ni,Ir films, Ni(CH3 COO)2 ·4H2 O was added to the second solution with specific weighted amounts for 1.5%, 3.0%, and 4.5% Ni-doped SnO2 :Ir structures. The spin coating process was carried out on pre-cleaned and dried glass substrates, and at 2500 rpm for 25 s, followed by drying for 15 min at 200 ◦ C. The films were subjected to heat treatments at 450 ◦ C for 3.0 h in a controlled air furnace followed by cooling the furnace to RT overnight
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