Photovoltaic - Electrolysis Cells

Photovoltaic Electrolysis Cells. These cells produce both fuel (e.g. H2) and electrical power by means of a low-energy electrochemical reaction such as the dissociation of HI. The principle of this cell is shown in Figure 6.27. 

The photovoltaic electrolysis cell has twice as many semiconductor layers as the photochemical diode. 

In the photovoltaic electrolysis cell the photoactive junctions are p-n junctions between two semiconductors, while in the photochemical diode the photoactive junctions are between semiconductors and aqueous solutions. 

In the photovoltaic electrolysis cell, the n-type region of the device, covered with a metal layer, becomes a cathode while the p-type region covered with a metal layer becomes an anode (i.e. it behaves like a majority carrier device) in the photochemical diode, the opposite is true, i.e. it is a minority carrier device with the n-type region acting as anode and the p-type region acting as a cathode. 

The photovoltaic electrolysis cell must be covered on the illuminated side with a transparent conductor which forms an ohmic contact and is catalytic for the relevant gas evolution reaction. Metallic coatings consisting of small metal islands may also serve to stabilize the photoelectrodes against corrosion, catalyse the H2 evolution, and produce efficient photoelectrolysis. 

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