Photovoltaic cells hydrogen from water

PHOTOVOLTAIC CELLS CAN BE USED TO PRODUCE HYDROGEN FROM WATER... 

Tien HT, Chen JW (1989) Hydrogen generation from artificial sea water in a semiconductor septum electrochemical photovoltaic cell. Photochem Photobiol 49 527-530... 

Tien HT, Chen JW (1990) Hydrogen production from water by semiconductor septum electrochemical photovoltaic cell using visible light. Int J Hydrogen Energy 15 563-568... 

Power for industrial operations is supplied at present by electricity from coal, natural gas, and oil, working heat engines at overall efficiencies of < 35%. All can be replaced by fuel cells of various kinds operating for the next two to three decades on hydrogen from re-formed fossil fuels and as soon as possible by hydrogen from photovoltaics and the decomposition of water.20... 

The brute force approach to achieve this goal is to employ a solid-state photovoltaic cell to generate electricity that is subsequently passed into a commercial-type water electrolyzer. Although efficiencies obtained are relatively high, i.e., close to 8 %, these devices are very expensive. Hence the price of hydrogen produced this way cannot compete with conventional sources. The long-term outlook is better for systems that borrow their principles from natural photosynthesis (see Section 1.4.1 above). 

Ottova et al. looked at two-compartment semiconductor-septum electrochemical photovoltaic cells with cadmium selenide and cadmium selenide telluride for water photolysis [126], They used cells consisting of two chambers separated by a CdSe or CdSe/CdTe bipolar electrode. The bipolar electrodes were prepared by painting a CdSe slurry on a metal substrate or by ultrasound-aided electrodeposition from CdSe solution in ZnCl2. The photoresponse (voltage and current output) and hydrogen yield from photo-induced electrolysis of H20 in the dark chamber of the cell were evaluated as a function of CdSe preparation method. The ultrasound-aided deposition technique gave excellent coatings of CdSe. 

Figure 1, The platinized Chi a cell. The Chi a-free electrode is used as a half cell in a liquid-junction photovoltaic cell. In photolytic reaction, only the platinized Chi a electrode is used in the production of molecular hydrogen and oxygen from water.

If one wants to use p-type semiconductors where the water reduction can be obtained by illumination, one suffers from the small band gaps and has to apply an auxiliary external voltage. Such systems could be used for a photoassisted electrolysis where only part of the power needed comes from the direct light absorption in the semiconductor electrode. The additional voltage could be taken from a photovoltaic cell coupled in series to the electrolysis cell. A p-type tungsten selenide electrode appears suitable for this purpose because its conduction band is located somewhat above the hydrogen potential in acidic solution. 

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