Adsorption activity of Cu, Au and Ni solid electrodes in molten carbonates

The surface energy, the electric double layer capacity and the estance (the charge derivative of the surface tension) were analyzed as a function of the electric potential across copper, gold and nickel solid electrodes in the eutectic melt 62 mol% Li2CO3 + 38 mol% K2CO3 in a reducing atmosphere (80% H-2 + 20% CO2) at the temperature of 923 K. The metals were found to behave differently in a polarization interval that is positive with respect to the stationary potentials of the electrodes. The density of the positive electric charge at the copper electrode increased monotonically as the potential was shifted toward positive values. The density of the positive charge at the gold and nickel electrodes decreased in the potential interval more positive than the zero potential charge. The charge even acquired the negative sign at the gold electrode. This phenomenon is explained by the fact that adsorption of the salt phase anions at the interface is specific rather than electrostatic. The specific adsorption is accompanied by the charge transfer through the interface. This may be followed by formation of covalent bonds between the adsorbent and the adsorbate.