Embodiments of the invention relate to a method for preparing crystalline metal-organic frameworks (MOFs). The method includes the steps of providing an electrolyte solution in contact with a conductive surface, and applying a current or potential to the conductive surface in contact with the electrolyte solution. The electrolyte solution includes a protonated organic ligand, a metal ion, and a probase. Application of the reductive current or potential to the conductive surface produces the crystalline metal-organic framework (MOF) deposited on the conductive surface. The MOFs produced by the method may be incorporated into a gas separation membrane, a purification filter, and/or a sensor.