Materials
In the simplest terms, the mechanism of PECs is based on the conversion of light energy into electricity within a cell involving two electrodes. Then the electricity is used for different aspects such as water electrolysis. In theory, there are three options for the arrangement of photo-electrodes in the assembly of PECs:
- photo-anode made of a n-type semiconductor and a cathode made of metal;
- photo-anode made of a n-type semiconductor and a photo-cathode made of a p-type semiconductor;
- photo-cathode made of a p-type semiconductor and an anode made of metal.
According to the principle of PECs, the two basic requirements for materials used as photo-electrodes are optical function, required to obtain maximal absorption of solar energy, and catalytic function, required for other reactions such as water decomposition.
Consequently, the development of high-efficiency photoelectrodes that satisfy the requirements entails processing of the materials in order to achieve optimized properties in terms of performance characteristics, including high efficiency of solar energy conversion, durability in aquatic environments, and low cost.
TiO2 is primarily used in the PECs to achieve substantial efficiency. Including SrTiO3 and BaTiO3, this kind of semiconducting titanates, the conduction band has mainly titanium 3d character and the valence band oxygen 2p character. The bands are separated by a wide band gap of at least 3 eV, so that these materials absorb only UV radiation. Change of the TiO2 microstructure has also been investigated to further improve the performance, such as porous nanocrystalline TiO2 photoelectrochemical cells. Meanwhile, other non-oxide semiconductors such as GaAs, MoS2, WSe2 and MoSe2 are also used to in the PECs as the n-type electrode due to their stability in multiplicity of chemical and electrochemical steps in the photocorrosion reactions.
Read more about this topic: Photoelectrochemical Cell
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