Shape-directed rotation of homogeneous micromotors via catalytic self-electrophoresis

The purpose of this work is to demonstrate that platinum microparticles with asymmetric geometries move spontaneously in hydrogen peroxide solutions. We can rationally design these motions by controlling particle shape using nanofabrication techniques. We design particles with n-fold rotational symmetry that rotate about their axis at rates specified by their extent of shape asymmetry. Experiments support a self-electrophoretic propulsion mechanism, where anodic oxidation and cathodic reduction of hydrogen peroxide occur at different rates at different locations across the particle surface. We develop a model to explain how the transport-limited electrochemical decomposition of hydrogen peroxide across an asymmetric particle surface leads to electro-osmotic flows that drive particle motion. Our results suggest that geometric control is an effective method to encode micromotor dynamics at the individual particle level. Insights from our proposed mechanism should be useful to design catalytic micromachines with complex dynamics and functions.