The breathing behavior of the MIL-53(Cr) metal-organic framework (MOF) has been explored previously upon guest-adsorption and thermal and mechanical stimuli. Here, advanced molecular simulations based on the use of an accurate force field to describe the flexibility of this porous framework demonstrate that the application of an electrical field induces the structural switching of this MOF leading to a first-order transition and a volume change of more than 40%. This motivated us to electrically tune the pore size of MIL-53(Cr) with the idea to propose a new concept to selectively capture CO2 over CH4 via a molecular sieving that paves the way toward the optimization of current separation-based processes.