Processing methods electrochemical vapor deposition

The development of new and improved electrocatalysts begins with the discovery of materials displaying improved intrinsic electrochemical activity. Intrinsic activity is best observed and compared in a well-controlled catalyst environment where variables that may disguise the intrinsic activity trends are minimized or absent. Particle size, particle size distribution, surface area, catalyst utilization and the distribution of crystallographic phases are parameters that are typically difficult to control. Vapor deposition of unsupported thin film electrocatalysts eliminates many of these variables. This method provides a controlled synthetic route to smooth, single-phase or multi-phase, ordered or disordered metal alloy phases depending on deposition and processing conditions. 

Electrodeposition of Pt on multiwall carbon nanotubes (MWNT) has been reported by Wang et al.27 In their process, a layer of Co was first electrodeposited on a carbon paper. The purpose of Co film was to catalyze the growth of the subsequent MWNTs layer. A chemical vapor deposition (CVD) technique was used to deposit MWNTs on the Co film. Platinum was then electrodeposited on the MWNT layer. The electrolyte used contained H2PtCl6 and H2SO4. The electrodeposition of Pt was performed under potentiostatic condition using 0 V vs. saturate calomel electrode (SCE). The particle size achieved with this technique was approximately 25 nm that is too large in comparison with other chemical and electrochemical methods. 

In general, for the deposition of thin films used in microelectronics, low-pressure processes, such as sputtering and low-pressure chemical vapor deposition (LP CVD), are preferred over the older, conventional chemical methods such as electroplating because deposition from an aqueous solution produces poorer quality films. On the other hand electrochemical and electroless metal deposition from solution are gaining renewed interest with micromachinists because of their emerging importance to LIGA. 

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