Figure 3 - Chemically fuelled autonomously moving objects.

The fuel applied is hydrogen peroxide. The propulsion is attributed to the decomposition of H₂O₂ to H₂O and O₂ creating a local oxygen concentration gradient and/or a difference in surface tension leading to translational movement. a, A striped Pt/Ni/Au/Ni/Au nanorod and the trajectory path of a nanorod spelling the letters 'PSU' in 5 wt% aq. H₂O₂. Reproduced with permission from ref. 42. Copyright (2005) Wiley. b, Design of an autonomous moving microparticle and the trajectory followed by the particle on H₂O₂ decomposition (the black spots indicate O₂ bubble formation). In this system a molecular catalyst is anchored to an 80 m silica particle. Note the difference in the mechanism for movement in these systems (oxygen gradients/surface tension or pressure from bubble formation). Figure reproduced from ref. 45 by permission of The Royal Society of Chemistry.