- Jang, Bumjin and Wang, Wei and Wiget, Samuel and Petruska, Andrew and Chen, Xiangzhong and Hu, Chengzhi and Hong, Ayoung and Folio, David and Ferreira, Antoine and Pané, Salvador and Nelson, Bradley
We report the partial core-shell nanowire motors. These nanowires are fabricated using our previously developed electrodeposition-based technique, and their catalytic locomotion in the presence of H2O2 is investigated. Unlike conventional bimetallic nanowires that are self-electroosmotically propelled, our Au/Ru core-shell nanowires show both a noticeable decrease in rotational diffusivity and increase in motor speed with nanowire length. Numerical modelling based on self-electroosmosis attributes the decreases in rotational diffusivity to the formation of toroidal vortices at the nanowire tail, but fails to explain the speed increase with length. To reconcile this inconsistency, we propose a combined mechanism of self-diffusiophoresis and electroosmosis based on the oxygen gradient produced by catalytic shells. This mechanism successfully explains not only the peculiar speed increase of Au/Ru core-shell nanomotors with length, but also the large variation in speeds among Au/Ru, Au/Rh and Rh/Au core-shell nanomotors. The possible contribution of diffusiophoresis to an otherwise well-established electroosmotic mechanism sheds light on future designs of nanomotors, at the same time highlighting the complex nature of nanoscale propulsion.