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1.1. STATEOFTHEARTELECTRODES 5 chapter. Based on the findings in the review, the selectivity issue in the chlorate and chlor-alkali processes has been investigated in a broader sense, by perform- ing also studies of how electrolyte contamination affects the decomposition of hypochlorite[14]. Still, a main focus has been put on the influence of electrode structure and composition[15–20], and I will therefore summarize the present sta- tus of anodes in chlor-alkali and sodium chlorate production and of activated cath- odes for HER in Section 1.1. I have made use of first principles modeling to gain a further understanding of the connection between composition, activity and se- lectivity, and to clarify the connection between experimental X-ray photoelectron spectroscopic (XPS) results and the actual electrode structure. As the application of such theoretical methods to problems in heterogeneous (electro)catalysis and materials science is recent, Chapter 2 contains a thorough overview of these meth- ods, and their application in the study of solid materials, (electro)catalysis and X-ray photoelectron spectroscopy. Experimental methods employed in this thesis are reviewed in Chapter 3. The results are presented and discussed in Chapter 4, and some conclusions and an outlook for future work is presented in Chapter 5. 1.1 The state of the art of electrodes used for the in- organic electrosynthesis of chlorine, sodium chlo- rate and hydrogen 1.1.1 Anodes for chlor-alkali and sodium chlorate production As has already been mentioned, DSA are used for the oxidation of Cl– in both processes. Dimensionally stable anodes were invented by Henri Beer in the 1950- 1960s[21]. Previously, graphite anodes had been applied, but these electrodes were consumed during use, requiring frequent adjustment of the anode position. Beer realized that since titanium forms a highly corrosion-resistant TiO2 oxide layer when used as an anode, it could be used as a stable anode support material in chlor-alkali electrolysis[22]. The current DSA coating developed in several steps. First, Beer suggested that deposition of noble metals onto titanium should serve to activate the anode. If a part of the active coating would be removed from the sur- face, the anode would not be destroyed since corrosion-resistant TiO2 would form. Beer tried depositing noble metals, such as platinum, on the surface of titanium, to activate the electrode, and patented the procedure[23]. However, the stability of this coating was found to be insufficient during industrial testing[21, 22, 24]. As a next step, the deposition method was changed from electrodeposition to a method consisting of painting a noble metal salt solution onto titanium. The painted ti- tanium was then heated in air at temperatures between 400−500◦C, converting the salt into what was thought to be metallic form. Different coating solutions,PDF Image | Studies of Electrode Processes in Industrial Electrosynthesis
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