Particle tracking experiments Particle tracking experiments were performed on using a Nikon Upright LV150N microscope (20x). Stock H 2 O 2 (30 v/v%, Acros Organics) was added to dilute particle suspensions of the Pt-functionalised microswimmers to obtain 300 uL of a fuel rich (0.5 v/v% H 2 O 2 ) solution. 280 µL thereof was then pipetted into a flow-through cell (cell 137-QS; Hellma Analytics) with a light path length of 1 mm. Videos were taken at 10 fps on a Hamamatsu C14440-20UP digital camera. Particle trajectories were then analysed using the MATLAB implementation of the Crocker and Grier IDL particle tracking method (25) and in-house MATLAB scripts.