Low-Voltage Electrophoretic Deposition in Water with Metal–Organic Framework Nanoparticles
Abstract
Electrophoretic deposition (EPD) constitutes a major industrial method for solution-processed fabrication of thin films and coatings. Conventional protocols require high applied voltages (50–1000 V) that induce parasitic electrochemical reactions, limit substrate compatibility, and create safety hazards. Here, we demonstrate that intrinsic surface charge density of size-controlled metal–organic framework (MOF) nanoparticles, together with particle size and solvent properties, governs electrophoretic mobility and enables high-quality EPD in aqueous media at 1 V, well below the threshold for water electrolysis. Compact, uniform films of MOF nanoparticles with thicknesses >10 μm deposit in 30 min, due to higher ζ-potentials and electrophoretic mobilities that improve with smaller particle sizes, whereas nonporous colloids require hours. Deposition occurs on a wide range of conductive substrates, enabling real-time monitoring of film thickness with quartz crystal microbalance devices and, as a result, the formation of redox-intercalation thin films with programmable capacitance and ion-insertion kinetics. These results provide an energy-efficient, safer, and rapid method for uniform thin-film assembly with thicknesses controlled to nanometer resolution.