Preventing the coffee-ring effect and aggregatesedimentation by in situ gelation of monodispersematerials

摘要

Drop-casting and inkjet printing are virtually the most versatile and cost-effective methods for depositingactive materials on surfaces. However, drawbacks associated with the coffee-ring effect, as well asuncontrolled aggregation of the coating materials, have impeded the use of these methods forapplications requiring high control of film properties. We now report on a simple method based oncovalent cross-linking of monodisperse materials that enables the formation of thin films withhomogeneous thicknesses and macroscale cohesion. The coffee-ring effect is impeded by triggeringgelation of the coating materials via a thioacetate–disulfide transition which counterbalances thecapillary forces induced by evaporation. Aggregates are prevented by monodisperse building blocks thatensure that the resulting gel resists sedimentation until complete droplet drying. This combined strategyyields an unprecedented level of homogeneity in the resulting film thickness in the 100 nm to 10 mmrange. Moreover, macroscale cohesion is preserved as evidenced by the long-range charge transferwithin the matrix. We highlight the impact of this method with bioelectrocatalysts for H2 and NADPHoxidation. Peak catalytic performances are reached at about 10-fold lower catalyst loading compared toconventional approaches owing to the high control on film cohesion and thickness homogeneity, thussetting new benchmarks in catalyst utilization.