Effect of confinement on the hydration and diffusion of chloride at high temperatures

•Effect of confinement on hydration of chloride in supercritical water is evaluated.•Diffusion coefficients and hydration numbers of chloride are affected.•Local water density is greatest on the surfaces. Molecular dynamics simulations were conducted of a chloride ion in high temperature water confined between parallel iron hydroxide surfaces. Simulated temperatures were 567, 715, 814 and 913K with densities ranging from 0.620 to 0.044gcm−3, and surfaces spaced at 10, 20 and 80Å apart. Radial distribution functions, coordination numbers, diffusion coefficients, and density profiles across the gap are provided. Hydration numbers increased as the spacing of the surfaces increased and diffusion coefficients were seen to be lower than their values for chloride in bulk water. The chloride was observed to have a diffusion coefficient an order of magnitude less than that of water and showed less dependence on the spacing of the surfaces. The effect of confinement on the water structure was seen to disappear at 80Å.