The velocity of self-propelled Pt-coated colloids is determined by the substrate.

Active colloids are typically found self-propelling near a substrate. However, the effect of the substrate on the self-propulsion remains unexplored. Here, we investigate whether the substrate influences the self-propulsion by performing systematic experiments on different substrates. Interestingly, we find that the colloid velocities are considerably different on different substrates. We consider various physicochemical properties as the origin for this observation. Our results are useful for future modeling and might be helpful in understanding the details of the still debated self-propulsion mechanism.