Poly 3-Hexylthiophene as a photocathode for solar water splitting

The focus of this research is to determine the extent to which poly 3-hexylthiophene (P3HT) can be used as a photoelectrode for solar water splitting. Research in the area of solar water splitting mostly focuses on inorganic materials but conjugated polymers, such as P3HT, offer several advantages. Most metal oxides used as photoelectrodes are only able to carry out water oxidation, require thick films to absorb significant amounts of light, and absorb light mainly in the ultraviolet part of the sun’s spectrum. Conjugated polymers are able (thermodynamically) to reduce protons, require thinner films, and absorb mostly in the visible region of the electromagnetic spectrum. Additionally, conjugated polymers are processed from solution at room temperature and pressure, and can be cast onto many different types of substrates (rigid or flexible). The ability of P3HT, on its own, to produce hydrogen gas (H2) from acidic aqueous solution is first examined. Figures of merit such as photocurrent and incident photon to current efficiency as a function of thickness are determined through photoelectrolysis in a homemade cell. In addition, the oxidation state of the polymer film in contact with aqueous acid area investigated using spectroelectrochemistry. Platinum was also employed as a hydrogen evolution reaction (HER) catalyst, either by photoelectrochemical deposition of nanoparticles directly on the polymer or as a colloidal dispersion.Thermodynamically, P3HT should reduce protons following light absorption. However, no H2 was detected in the absence of a HER catalyst. Hydrogen was produced when platinum was photoelectrochemically deposited. This deposition technique resulted in the formation of Pt nanoparticles on the polymer film. Also, this demonstrates that a single layer conjugated polymer device is capable of performing H2 evolution under illumination.