Solar Generation of Hydrogen using Titanium Oxide Nanoparticles: Impact of Size on Stability and Efficiency

Abstract

The efficiency and stability of a photoelectrode are important factors in developing photoelectrochemical cells (PEC) for the renewable production of solar chemicals and fuels. Thin films of thicknesses of 5 µm were prepared by the doctor-blading technique using the pure TiO2 nanoparticle with sizes ranging from 5 to 100 nm. A 2-electrode system was utilized in order to measure solar to hydrogen efficiency (STH) related to whole cell efficiency and a 3-electrode system was used to examine intrinsic solar to chemical efficiency (ISTC). The stability of photoelectrodes was tested by running a long term STH test under illumination from the front and back side. The optimum particle size in terms of stability and efficiency, with regards to the STH test, was 30 nm. Results clearly indicated that the size of the TiO2 nanoparticle affects the surface area in order to absorb photon energy, and charge carries dynamics to transfer generated electrons and holes for oxidation and reduction reactions. Also, it was revealed that illuminating the cell from the backside would increase both the STH efficiency of the cell and the operational lifetime of the photoelectrode in the alkaline aqueous electrolyte.