Motion-Controlled Photocatalytic Hydrogen Evolution Using Microrobots Designed with a Single Atomic-Level Precision

The potential of hydrogen as a next-generation fuel has recently attracted a great deal of attention because it is considered a green fuel originating from renewable sources. Material sciences with the tools of nanoarchitectonics are targeting a wide variety of suitable photocatalysts of different materials, morphologies, and dimensionalities. Here, we present the concept of the photocatalytic hydrogen evolution reaction (HER) using microrobots: tiny autonomous devices possessing propulsion and photocatalytic abilities. The microrobots were derived from a black TiO₂ (bTiO₂) material that provided the photocatalytic properties that contributed not only to successful light-induced propulsion but also to the activity toward the HER. In the next step, the decoration with magnetic nanoparticles (NPs) enabled the navigation of microrobots (mag-bTiO₂ microrobots) in a magnetic field to enhance overall propulsion abilities and to allow their collection and consecutive reusability. As a result, mag-bTiO₂ microrobots showed efficiency as dynamic photocatalysts for the HER; the positive contribution of the "on-the-fly" mode was confirmed by a control experiment using mag-bTiO₂ microrobots as static photocatalysts. Furthermore, the overall efficiency of the HER was improved by decorating microrobots with atomic-level Pt species (mag-Pt-bTiO₂ microrobots). The findings of this proof-of-concept study demonstrate an alternative approach toward the photocatalytic HER and lay the basis for the next generation of nano/microrobots for energy conversion applications.