Tadpole‐Shaped Catalytic Janus Microrotors Enabled by Facile and Controllable Growth of Silver Nanotails

Abstract

AbstractMicrorotors are an indispensable component in micromachines, yet their usefulness has been limited by a lack of simple, inexpensive, and controlled fabrication technique that yields microrotors of controlled shapes in large quantities. To address this challenge, the chemical synthesis, characterization, and activation of tadpole‐shaped catalytic microrotors that consist of a spherical, platinum (Pt)‐coated head and a silver (Ag) nano‐tail of tunable lengths are reported herein. Importantly, this tail spontaneously grows on Pt in an aqueous solution of Ag+ and hydrogen peroxide (H2O2), at a speed of ≈100 nm s−1, preferably along the Ag (111) plane. The growth of Ag nanowires is attributed to an electrochemical reaction occurring on a tapered Pt cap, a mechanism corroborated by control experiments with photo‐active titania microspheres, which introduce the additional advantage of light‐controlled growth. The presence of a long Ag nano‐tail on a tadpole‐shaped microrotor breaks its symmetry and induces rotation in H2O2, and its structure‐dependent dynamics is quantitatively studied and supported by numerical simulation. The chemical synthesis of microrotors with Ag nano‐tails will introduce new designs of micromachines of controlled dynamics, as well as functional materials and devices where mild, controllable, and facile growth of Ag nanostructures is desired.