Investigation of chloride ion adsorption onto Ti2C MXene monolayers by first-principles calculations

Chloride ion adsorption on Ti2C monolayers was theoretically investigated. Electrochemical parameters, including specific capacity, chloride ion (Cl-) diffusion barrier, and discharge voltage profile, were studied via first-principles calculations. The most favorable Cl- adsorption configuration was identified using a partial particle swarm optimization algorithm and the results showed that Cl- adsorption onto Ti2C monolayers achieved a large theoretical capacity (331 mA h g(-1)), high working voltage (4.0-3.5 V), and low diffusion barrier (0.22 eV). This resulted in excellent rate capability and a large specific energy of 1269 W h kg(-1) at the material level. The effects of terminal O, F, and OH groups on Cl- adsorption onto Ti2C monolayer were also studied, which showed that Cl- could not be adsorbed onto O and F terminated Ti2C monolayers. In comparison, Cl- adsorption onto OH terminated Ti2C was allowed but generated a smaller specific capacity (126 mA h g(-1))and lower working voltage (3.5-1.5 V) than a bare Ti2C monolayer.