Cathode plasma spray

White BD, Kesler O, and Rose L. Air plasma spray processing and electrochemical characterization of SOFC composite cathodes. J. Power Sources 2008 178 334—343. 

Fig. 14. Comparison of the current-voltage curves of a smooth nickel cathode and two different Raney-nickel-coated cathodes posessing comparable loading and effective surface (a) smooth nickel. Raney nickel prepared from two different precursors (b) plasma-sprayed NiAh, (c) NiAU cold rolled together with Mond nickel.

The method of preparation is the most crucial and usually the least controllable variable, so much that it is usually taken as the last chance to explain any inconsistent behaviour. Unfortunately, this remains the least understood parameter, but also the most open one to originality and inventiveness. It is hard to list all methods, also because in many cases details have been left purposely obscure. However, to a first approximation, cathodes can be coated with an active layer by (i) electrodeposition [142], (ii) thermal decomposition [143], (iii) flame and plasma spraying [144-146], (iv) in situ activation [147, 148]. Cathodes may also be prepared from the powder... 

Fig. 19. Tafel lines for hydrogen evolution in 30 wt% KOH, 80 °C, on plasma-sprayed Ni cathode coatings reduced under H2 atmosphere for 30 min at different temperatures. (1) Electrode as prepared (2) Reduced at 200, (3) 300, (4) 400, (5) 500 °C. After ref. 386, by permission of Chapman Hall.

The electrolyte (YSZ) layer ( 40 fim thick) is applied to the cathode by EYD (see Section 3.6.9). Because this is an expensive route efforts are made to use more cost-effective methods, for example plasma-spraying and electrophoretic deposition followed by sintering. 

Using the aluminum sheet substrate as the cathode of a direct current (DQ glow discharge, cathodic plasma polymerization is carried out. Dealing with metal surfaces, cathodic plasma polymerization is the most practical means to provide the best corrosion protection (see Chapter 13). A primer is applied on the surface of the plasma polymer. The thickness of the plasma polymer is roughly 50 nm on average and that of the primer layer is about 30,000 nm (30 pm). Primers used included E-coat (electrolytic deposition of paint) and spray primers, but no top coat was applied in the study of corrosion protection. 

Asahi Kasei s electrolyzers use NiO cathodes that are resistant to impurities and current interruptions [191]. They are prepared by plasma spraying a mixture of NiO and Cr203 or a Ti02 promoter onto nickel-plated steel. The loading of the catalyst mixture is 0.10-0.15 gcm . This cathode has been used for more than 15 years in conunercial operations. 

H. Houda, Y. Naoki, and H. Obanawa, Characteristics of Plasma-Sprayed NiO Cathode and Mechanism of Hydrogen Evolution Reaction at its surface. In Proc. Vol 98-10, The Electrochemical Society Inc. (1998), p. 329. 

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