Visible-Light-Driven, Nickel-Doped Cobalt Oxides/Hydroxides Actuators with High Stability

Material-based, light-driven actuators have been a recent research focus for the development of untethered, miniaturized devices and microrobots. Recently introduced nickel hydroxide/oxyhydroxide (Ni(OH)₂/NiOOH) and cobalt oxides/hydroxides (CoO(OH)) are promising light-driven actuators, as they exhibit large and rapid actuation response and are inexpensive to fabricate by fast electrodeposition. However, as their actuation is due to the volume change accompanying the light-induced desorption of intercalated water in their turbostratic structures, their actuation reduces over time as crystallization takes place slowly, which lowers the amount of water held. Here, we introduce nickel-doped cobalt oxides/hydroxides (NiCoO(OH)) actuator that exhibits similar turbostratic crystal structures and actuation magnitude as CoO(OH), but with much slower crystallization and hence significantly more stable actuation than CoO(OH) or Ni(OH)₂/NiOOH. The new actuator exhibits much better applicability than the Co and Ni counterparts, and the present work shows that a stabilized turbostratic structure is a key for achieving high light-driven actuation in transition-metal oxide/hydroxide actuators.