Electrolysis performance, comparative water

In summary, MEA fabricated based on SPEK was much cheaper than that based on Nation for achieving a comparable performance in water electrolysis. Therefore, it would enable a more economically competitive hydrogen production by SPE water electrolysis. To accomplish this goal, however, more detailed woric is needed, including MEA fabrication impiovanent, MEA active area scale-up, and stability experiments. 

For cases directly comparable to the cyclization originating from (27) above, the yields of the product were not as high. However, a related reaction used in the synthesis of an 11-substituted dibenzo[a,d]-cycloheptenimine derivative was very successful as shown in Scheme 11 (Eq. 2) [32]. In this reaction, a controlled potential electrolysis of (33) led to the formation of the tetracyclic (34) in an 85% isolated yield. The reaction was performed on a 1 g scale using an undivided cell, a graphite felt anode, a stainless steel cathode, a saturated calomel reference electrode, and a 1% NaBF4 in 70 30 THF/water electrolyte solution. The electrolysis was scaled up further with the use of a flow cell. In this experiment, 200 g of (33) were oxidized in order to afford a 75% isolated yield of (34). 

Two further improvements in cell performance have occurred using polypyrrole films. One noted by Fan et al (41) precoats an n-Sl surface with a thin film of Au( 15A) followed by a thicker film of polypyrrole (3300A). Such a combined electrode substantially Improves stability in aqueous electrolytes containing the couple. The other improvement is due to Cooper et al (44) who sputter deposited a 72A "film" of Pt on the surface of a polypyrrole film covering a Ta substrate. (Ta is known to form surface oxides like n-Si). They were then able to sustain O2 evolution by water electrolysis in a manner indistinguishable from the use of naked Pt electrodes. Their results show that small deposits of Pt at the polymer/electrolyte lower the overvoltage necessary for water oxidation compared to that needed using non-platinized polypyrrole. 

In 1973, Mikheev et al. reported that a stable, monovalent Md ion could be produced in ethanol solutions and that it co-crystallized with CsQ [45]. However, Samhoun and co-workers studied the overall reduction of Md to the amalgam using controlled potential electrolysis they concluded that Md could not be considered a cesium-like element and no evidence was obtained consistent with a monovalent state [46,47]. Hulet et al. have recently repeated some of the co-crystallization experiments of Mikheev and performed a series of new experiments in an attempt to prepare Md by reduction with Sm in ethanol solutions and also in fused KQ media [37]. In these experiments, the behavior of Md was compared to tracer amounts of 3-i-, 2-i-, and 1-i-ions and Md consistently followed the 2 -i- ions. They concluded that Md cannot be reduced to a monovalent state with Sm as daimed by Mikheev. However, on the basis of the results of thermodynamic studies of the co-crystallization process of mendelevium with chlorides of alkali metals, the Russian investigators maintain that Md can be reduced to the monovalent state in water-ethanol solutions and that the co-crystallization of Md with salts of divalent ions can be explained as being due to the formation of mixed crystals [102,103]. An ionic radius of 1.17 A was calculated for Md from the results of the co-crystallization studies [104]. 

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