Preparation and electrochemical characterization of carbon films in UHV environments

The electrochemical properties of carbonaceous films prepared by catalytic chemical vapor deposition on clean Ni(111) using an equimolar CO:CH₄ mixture at a total pressure ca. 2 × 10_-5 kPa (0.133 kPa = 1 Torr) as carbon source have been examined under ultrahigh vacuum (UHV) conditions (6.7 × 10_-11 kPa) in pre-electrolyzed LiClO ₄-poly(ethylene)oxide, (PEG), solutions (1 Li⁺:36 ethylene oxide units) at ca. 55°C. All steps involved were carried out in the same UHV chamber under highly controlled conditions without exposure to the ambient atmosphere. Despite these precautions, the first scan for the supported carbon film, C/Ni(111), in the negative direction initiated at ∼2.0V vs. Li/Li ⁺ extending down to 0.05 V, yielded a total negative charge exceeding by about one-third that observed in the subsequent scan in the positive direction. This irreversible capacity loss was much reduced during the second and subsequent cycles. Nevertheless, well-defined cyclic voltammetric peaks could be clearly discerned over the featureless background observed for clean Ni(111) in the potential region 1.2 < E < 0.05 V vs. Li/Li⁺. Based on coulometric data and the total amount of carbon in the film as determined from AES analysis the Li⁺/C stoichiometric ratio was estimated to be 1:3.