Identification of Surface Films Formed on Active Metals and Nonactive Metal Electrodes at Low Potentials in Methyl Formate Solutions

The electrochemical behavior of methyl formate (MF) and MF/CO₂/Li salt solutions with active metals (lithium, calcium) and nonactive metals (nickel, gold) was investigated. The salts included calcium, lithium, and tetrabutylammonium perchlorates and tetrafluoroborates, and LiAsF₆. Surface-sensitive Fourier transform infrared (FTIR) spectroscopy and X-ray microanalysis were used in order to characterize the various electrode surfaces, in addition to cyclic voltammetry. It was found that the metal formates (HCOOLi or (HCOO)₂Ca) are the major surface species formed both on the active and on the nonactive electrodes at potentials below 1.5 V (Li/Li⁺) and that they passivate them. When CO₂ and Li salt are present in MF solutions, films formed on both active and nonactive electrodes at low potentials contain both lithium formate and lithium carbonate.