Protective coating for MCFC cathode: Low temperature potentiostatic deposition of CoOOH on nickel in aqueous media containing glycine

The corrosion and dissolution of the state-of-the-art nickel cathode is one of the major problems for the development of the molten carbonate fuel cell. In order to protect this cathode, electrochemical potentiostatic deposition, a cheap and low-temperature technique, was used to produce CoOOH coating. It is well known that the lithiated cobalt oxide (LiCoO2, stable from produced at 650 °C in molten carbonates) is significantly less soluble than nickel oxide. Potential–acidity diagrams of the cobalt–water system with the presence of a complexing agent, glycine, established from a new critical data set, allowed to predict the thermodynamic stability of CoOOH in a range of 25–80 °C. The deposition process was optimised on dense nickel substrates, analysing thoroughly the effect of the temperature, imposed potential, pH, electrolysis duration and the role of glycine. The structure and morphology of the thin layers prepared were characterised by X-ray diffraction and scanning electron microscopy (SEM). XRD measurements showed the presence of the characteristic CoOOH lines in varied experimental conditions. The CoOOH coatings were spontaneously transformed into LiCoO2 in the molten carbonate melt. Preliminary results, obtained from ex situ and in situ techniques, on their behaviour and stability in MCFC conditions are given here.