Monograin membrane

Dining the last couple of years CdS-containing Nafion membranes have been apphed for the photocleavage of H2S . They are not comparable with the monograin membranes because the CdS particles are at randomly distributed in a rather thick Nafion membrane. This technique is attractive for some applications because the semiconductor particles are immobilized . On the other hand, problems may arise because of diffusion problems in the nafion membrane. Mainly the photoassistol Hj-formation at CdS was investigated in the presence of a Pt-catalyst and with coprecipitated ZnS CdS without a catalyst . 

Meissner et al. proposed a monograin-membrane technique with which short circuits can be avoided at the suspended particles and which makes it possible in principle to separate the anodic and cathodic reactions. The membrane consists of... 

Light-Induced Generation of H2 at CdS-Monograin Membranes. A polyurethane film is embedded with CdS particles to compartmentalize HER and OER sites. See also text (Section 2). 101... 

Frequently, reactions have been investigated at particles loaded with a catalyst such as a metal (Pt) or a metal oxide (RUO2). Such catalysts enhance the reaction rate, and sometimes other products are formed. This has been discussed in detail in various papers [114,183]. Although it is generally assume that for instance noble metals (Pt) catalyzes a reduction process such as H2-formation, it is impossible to get information whether the reduction or the oxidation occurs via the catalyst. Few years ago, a semiconductor monograin membrane technique was developed by which the particles are fixed, as illustrated in Fig. 39... 

Fig. 9.16 Energy band model for particles embedded in a monograin membrane. (Compare with Fig. 9.1,5).

The monograin technique has only been applied so far to CdS and SiC. Since the production of the monograin membranes is not easy and rather big particles (= 10 pm) are required, this technique has not been used much yet. 

FIG. 3 Schematic view of the macroscopic monograin membrane suggested in Ref. 4 as an efficient tool for photocatalytic production of hydrogen at the expense of oxidation of some electron-donating compounds. The thickness of the polymeric membranes in the experiments was a few micrometers. 

Figure 9.15 Reactions at semiconductor monograin membranes (after [43]).

Figure 11.24 (a) CdS monograin and the structure of the cell with 2 compartments, (b) Hydrogen evolution vs time at one side, sulphide oxidation at the opposite side of the membrane... 

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