The transition to a green global economy requires the fast development of alternative fuel production. In this sense, photoelectrochemical water splitting to generate green hydrogen is an outstanding strategy. Nevertheless, this technology is far from an industrial application due to issues related to light absorption, charge transfer, and long-term stability. Most of the studies on this topic look for high photoconversion efficiencies and neglect important aspects such as structure, morphology or specific charge transfer mechanisms. In this work, we present insights into titanium dioxide photoanodes fabricated by chemical vapor deposition (CVD) on Indium Tin Oxide (ITO) and modified with carbon nanomaterials. Ttitanium tetraisopropoxide (TTIP) was used as precursor. In a first strategy, oxidized carbon nanotubes (CNTs-nox) were employed as a charge-transfer layer between ITO and TiO2. In a second strategy, acetylene was introduced simultaneously to TTIP decomposition to obtain carbon-modified titanium dioxide (TiO2©) in a single synthetic step. Photoanodes were characterized by several techniques, including Scanning Electron Microscopy, X-Ray Diffraction, Raman, X-ray photoelectron spectroscopy, and UV-Vis (Diffuse Reflectance). Photoelectrochemical (PEC) performance was measured in a three-electrode cell (Pt(CE) and Ag/AgCl (RE)) using simulated sun-light and UV-Led Light. The results showed that the extent of carbon nanotube oxidation was directly related to the morphological, optical, and photoelectrochemical performance of CNTs-nox/TiO2 photoanodes. Also, CNTs allowed the formation of a TiO2 layer with an improved surface area and better light absorption. PEC experiments showed that the main role of CNTs is to improve charge transfer, neglecting surface recombination and hole accumulation. An optimal photocurrent of 0.25 mA (0V vs Ag/AgCl(1M)) was achieved for the optimized CNTs-nox/TiO2 photoanode. For TiO2© photoanodes, the results proved that the amount of acetylene employed was the main factor in the properties of the photoanodes. Small amounts of C2H2 lead to TiO2© photoanodes with improved performance (0.3 mA/cm2 at 0V vs 0.1 mA/cm2 (0V) for unmodified TiO2), while high amounts produced a material with poor PEC performance and high recombination. The outcome of this work is very relevant for developing new PEC devices by introducing carbon nanomaterials, allowing better control of PEC performance through material modification.

Carbon modified titanium dioxide photoanodes: Effects of carbon nanotubes introduction and carbon doping in the morphological, optical, and photoelectrochemical response

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