Reversing a Platinum Micromotor by Introducing Platinum Oxide.

Understanding and controlling the swimming direction of a synthetic nano- and micromotor holds fundamental and applied significance. Here, we focus on platinum-containing Janus colloids that catalytically decompose H 2 O 2 into O 2 , an archetypical model of chemical micromotor. We discover that platinum oxides (primarily PtO) are produced on Pt films sputter-coated in O 2 plasma, and PtO reverses the motor possibly by self-electrophoresis. Using this knowledge, micromotors moving in either direction were fabricated by intentionally introducing or removing PtO. These findings challenge the conventional wisdom that a Pt micromotor is powered by Pt alone, and open up new avenues for controlling the swimming directions of a micro- and nanomachine.