Abimbola Ayodeji Ashaju

• Transport Phenomena
• Colloids and interface science
• Multiphase flow transfer
• Electrochemistry
• Computational fluid dynamics

Electrocatalytic Induced Convective Flow

Project Description

The electrochemical decomposition of hydrogen peroxide  has been reported to generate interfacial fluid flow by micro-pumps [1], and interdigitated microelectrodes[2], as well as the motion of bimetallic platinum/gold nano-motors [3]. In principle, the immersion of platinum/gold nanorods in hydrogen peroxide, triggers a series of oxidation and reduction reactions , where  is oxidized at the platinum anode into protons, electrons, and oxygen molecules, while reduction takes place at the gold cathode. The resulting ionic flux generates an electric field that is coupled with the charge density, thereby inducing an electric body force that drives interfacial fluid motion. 

My PhD research focuses on the study of catalytic induced concentration, its potential gradients and the generated flow. The starting platform will be based on the hydrogen peroxide oxidation and reduction at metallic catalytic sites.  The initial devices will consist of bimetallic patterns, e.g. Au and Pt, with individual controlled electric potential.

•         The immobilized patterns allow the in situ observation of flow profiles, generated by the asymmetric surface reactions, using, OCT, microPIV and TIRF based PIV.
•         The evolution of protons will be experimentally probed using fluorescence lifetime imaging microscopy (FLIM) likewise also the pH and temperature profiles within the near surface regions in both conventional way as well as by using TIRF to access the very near surface region. Via potential and current measurements, simultaneous information on the electron flux is obtained and can be related to the observed concentration profiles.
•         The relation between the gradient and velocity profile will be studied, with respect to the interface characteristics like roughness and adsorption.
•         Amplification of electro osmotic flows by surface hydrophobic interactions

Our initial numerical simulations have predicted very interesting scaling relation between the velocity, potential and the metal reactivity ratio (or Damköhler ratio) [4]. The validity of these predictions will be further explored. Experimental measurements of local proton and hydroxyl concentrations and induced electric potential will allow the verification of these scaling relations. Further utilization efforts will be performed regarding water treatment catalysis, e.g. nitrite reduction and photocatalytic oxidation. Such aqueous based systems involve the consumption and production of ionic species, and hence will be suitable for interfacial osmotic transport.

[1]        T. R. Kline, W. F. Paxton, Y. Wang, D. Velegol, T. E. Mallouk, and A. Sen, “Catalytic micropumps: Microscopic convective fluid flow and pattern formation,” J. Am. Chem. Soc., vol. 127, no. 49, pp. 17150–17151, 2005.

[2]        W. F. Paxton, P. T. Baker, T. R. Kline, Y. Wang, T. E. Mallouk, and A. Sen, “Catalytically induced electrokinetics for motors and micropumps,” J. Am. Chem. Soc., vol. 128, no. 46, pp. 14881–14888, 2006.

[3]        T. R. Kline, W. F. Paxton, T. E. Mallouk, and A. Sen, “Catalytic Nanomotors: Remote-Controlled Autonomous Movement of Striped Metallic Nanorods**,” pp. 744–746, 2005.

[4]        S. M. Davidson, R. G. H. Lammertink, and A. Mani, “Convective Flows induced by Surface Reactivity Contrast,” pp. 1–15, 2017.