"Z-Axis" Thinking: Structural Coding Enables Programmable Motion of Catalytic Micromotors

Chemically propelled micro/nanomotors (CMNMs) generally need external fields or environmental cues to perform time-variable motion, severely limiting their ability to execute complex tasks and their application scenarios. This study introduces a z-axis structural encoding strategy for CMNMs, analogous to 3D integration in microelectronics, by radially stacking multilayers with different catalytic activities in sequence on one hemisphere of a particle. As a proof of concept, we demonstrate that polystyrene-Au-Pt Janus micromotors exhibit a time-variable shift from inert-side-leading to active-side-leading motion, with the transition time tunable through the thickness and microscale morphology of the outer metal layer. Experiments and phenomenological simulations show that the motion transformation mechanism is governed by the permeation dynamics of fuel H₂O₂ in the stacked outer metal layers, which enables H₂O₂ to reach the inner interface and switch the propulsion mechanism from Pt-catalyzed decomposition to Au-Pt bimetallic self-electrophoresis. For the as-designed CMNMs, the motion speed, leading-side orientation, and transition time can be programmed in temporal sequence by their intrinsic structure parameters, including the layer number, thickness, microstructure, and composition of the stacked active layers. This z-axis multilayer architecture strategy proposed herein provides a large room for CMNMs to encode versatile autonomous motions in a temporal sequence by an intrinsic structure.