Abstract
Photoelectrocatalytic hydrogen production was studied by using a photoelectrochemical cell where the photoanode was made by depositing on FTO electrodes either a nanoparticulate WO3 film alone or a bilayer film made of nanoparticulate WO3 at the bottom covered with a nanoparticulate TiO2 film on the top. Both the electric current and the hydrogen produced by the photoelectrocatalysis cell substantially increased by adding the top titania layer. The presence of this layer did not affect the current-voltage characteristics of the cell (besides the increase of the current density). This was an indication that the flow of electrons in the combined semiconductor photoanode was through the WO3 layer. The increase of the current was mainly attributed to the passivation of the surface recombination sites on WO3 contributing to the limitation of charge recombination mechanisms. In addition, the top titania layer may have contributed to photon absorption by back scattering of light and thus by enhancement of light absorption by WO3. Relatively high charge densities were recorded, owing both to the improvement of the photoanode by the combined photocatalyst and to the presence of ethanol as the sacrificial agent (fuel), which affected the recorded current by “current doubling” phenomena. Hydrogen was produced under electric bias using a simple cathode electrode made of carbon paper carrying carbon black as the electrocatalyst. This electrode gave a Faradaic efficiency of 58% for hydrogen production.
Highlights
Photoelectrocatalytic hydrogen production is one of the most popular research subjects because it promises an effective route for converting solar energy and storing it as chemical energy in the form of hydrogen
This work demonstrated the improvement of the photoelectrocatalytic behavior and the increase of the hydrogen production rate by adding a titania film on the top of a WO3 photoanode
The electrochemical characteristics of the photoanode were not modified by TiO2 film addition, but the obtained photocurrent largely increased, while the quantity of hydrogen proportionally increased as well
Summary
Photoelectrocatalytic hydrogen production is one of the most popular research subjects because it promises an effective route for converting solar energy and storing it as chemical energy in the form of hydrogen. The popularity of hydrogen stems from the fact that it has the highest gravimetric heat of combustion (~286 kJ/mole), while its combustion leads to the production of water. Hydrogen is mainly produced by reforming of fossil fuels. It can be produced by electrolysis using, for example, renewable electricity. 1.23 V are necessary to split water by electrolysis; in reality, much higher voltages and expensive electrocatalysts are necessary. In this sense, water splitting by photoelectrocatalysis [1] is a very promising approach since it necessitates much lower electric biases. Oxidation of water is a four-electron process: 2H2 O→O2 + 4H+ + 4e−
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