Photo assisted Electrolysis Cell

These cells operate under illumination in combination with a bias, which serves to either drive electrolytic reactions for which the photon energy is insufficient or to increase the rate of chemical energy conversion by reducing electron-hole recombination in the semiconductor bulk. Most commonly an electrical bias is provided to drive the reactions [36-41]. 

Chemically biased photo-assisted photoelectrolysis cell [42-45] 

A chemical bias is achieved by using two different electrolytes placed in two half-cells, with the electrolytes being chosen to reduce the voltage required to cause the chemical splitting. An n-Ti02 photoanode 4M KOH 4M HCl Pt-cathode is one example of a chemically biased photoelectrochemical cell [44]. 

This cell involves the absorption of light by dye molecules spread on the surface of the semiconductor, which upon light absorption will inject electrons into the conduction band of the n-type semiconductor from their excited state. The photo-oxidized dye can be used to oxidize water and the complementary redox process can take place at the counter electrode [46,47]. Tandem cells such as these are discussed in Chapter 8. 

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A review of photo-assisted electrolysis studies performed with p-type semiconductor photocathode/dark Pt anode systems suggests that a complementary phenomena arising from the presence of OH ions produced during the reduction half-cell reaction,... 

Consider a photo-assisted water electrolysis cell, incorporating a photoanode and dark metal cathode. Illumination of the n-type semiconductor photoanode with a depletion space charge region results in a net flow of positive vacancies, or holes, to the semiconductor/electrolyte interface. Here the hole (h+) may be accepted by the reduced form of the oxygen redox couple. 

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