Material-dependent performance of fuel-free, light-activated, self-propelling colloids

Self-propelling, light-activated colloidal particles can be actuated in water alone. Here we study the effect of adding different amounts of a gold/palladium alloy to titanium dioxide-based, active colloids. We observe a correlation between alloy-thickness and the average speed of the particles, and we discover an intermediate thickness leads to the highest activity for this system. We argue that a non-continuous thin-film of the co-catalyst improves the efficiency of water-splitting at the surface of the particles, and in-turn, the performance of "fuel-free" self-propulsion.