Low-Voltage Electrophoretic Deposition in Water with Metal-Organic Framework Nanoparticles

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.