Bromide electrosorption on liquid gallium: a typical example of halide electrosorption from aqueous solutions and its modeling

The adsorption of bromide ion on liquid gallium from aqueous solutions of NaBr + HBr of concentrations ranging from 0.02 to 1.99 M was determined on the basis of capacitive charge measurements carried out by a computerized chronocoulometric technique. This adsorption is parametrized by the use of the virial isotherm corrected for the potential difference across the diffuse layer. The resulting adsorption behavior has several features in common with chloride, bromide, and iodide adsorption on mercury. These general features are interpreted on the basis of a molecular model that accounts for the local potential at the position of an adsorbed anion created by the surrounding anions as well as by the water dipoles. The fundamental role played by the mutual interactions among the adsorbed anions, the adsorbed water dipoles, and the inhomogeneous electron gas, the latter treated on the basis of a simple one-parameter jellium model, is pointed out.