title: Bipolar electrochemical mechanism for the propulsion of catalytic nanomotors in hydrogen peroxide solutions.
abstract: Bimetallic nanorods are propelled in aqueous solutions by the catalytic decomposition of hydrogen peroxide to oxygen and water. Several mechanisms (interfacial tension gradients, bubble recoil, viscous Brownian ratchet, self-electrophoresis) have been proposed for the transduction of chemical to mechanical energy in this system. From Tafel plots of anodic and cathodic hydrogen peroxide reactions at various metal (Au, Pt, Rh, Ni, Ru, and Pd) ultramicroelectrodes, we determine the potential at which the anodic and cathodic reaction rates are equal for each metal. These measurements allow one to predict the direction of motion of all possible bimetallic combinations according to the bipolar electrochemical (or self-electrophoretic) mechanism. These predictions are consistent with the observed direction of motion in all cases studied, providing strong support for the mechanism. We also find that segmented nanorods with one Au end and one poly(pyrrole) end containing catalase, an enzyme that decomposes hydrogen peroxide nonelectrochemically, perform the overall catalytic reaction at a rate similar to that of nanorods containing Au and Pt segments. However, in this case there is no observed axial movement, again supporting the bipolar electrochemical propulsion mechanism for bimetallic nanorods.
authors.affiliation: Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: Yang
authors.initials: Y
authors.lastname: Wang
authors.forename: Rose M
authors.initials: RM
authors.lastname: Hernandez
authors.forename: David J
authors.initials: DJ
authors.lastname: Bartlett
authors.forename: Julia M
authors.initials: JM
authors.lastname: Bingham
authors.forename: Timothy R
authors.initials: TR
authors.lastname: Kline
authors.forename: Ayusman
authors.initials: A
authors.lastname: Sen
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Mallouk
mesh_terms: D002384:Catalysis; D004563:Electrochemistry; D006861:Hydrogen Peroxide / Q000737:chemistry*; D019216:Metals, Heavy / Q000737:chemistry; D008839:Microelectrodes; D036103:Nanotechnology; D043942:Nanotubes / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D010316:Particle Size; D012996:Solutions / Q000737:chemistry; D013499:Surface Properties; D013997:Time Factors; D014867:Water / Q000737:chemistry
chemical_list: D019216:Metals, Heavy; D012996:Solutions; D014867:Water; D006861:Hydrogen Peroxide; D010100:Oxygen