Electrochemistry: Electrocatalysis, Fuel Cells, in situ Synchrotron X-ray Techniques and Nanofabrication

Fuel Cell Materials

Fuel cells convert chemical energy of various fuels directly into electrical energy. They have about two times the efficiency of internal combustion engines and produce no pollutants or noise. Due to the pressing issues with limited and unstable supplies of fossil fuel resources, growing atmospheric pollution and greenhouse gas emissions aggravated by a projected increase in global power demand, fuel cells are on the fast development track to replace internal combustion engines as power sources for vehicular applications. All major car manufacturers in the US, EU and Japan made commitments to put fuel cell powered electromobiles on the road between 2010 and 2020.

My group conducts fundamental studies of the main fuel cell components: catalysts, membranes, and prorous electrodes. We are developing new routes for synthesis and screening of electrocatalysts. Fundamental studies of electrocatalysis mechanisms are done with single crystal electrodes. We extensively use synchrotron-based X-ray techniques such as Surface X-ray Scattering, X-ray Adsorption Spectroscopy and High-Resolution X-ray Fluorescence Spectroscopy to gain information on structure and activity of electrocatalysts under operating fuel cell conditions.

Also, we are working on development of polymer proton conducting membranes that do not contain water or water-soluble dopants. This should allow operation of polymer electrolyte fuel cells at temperatures above 120^oC and, hence, futher enhance the rates of electrochemical reactions.

Electrochemical reactions in fuel cells require the presence of a catalyst, electrons, protrons and reactant. As a result, they occur only in a narrow region where all of these components can meet. In conventional fuel cell electrodes, which are prepared by random mixing of composite particles, a significant number of expensive catalyst is wasted because they are not accessible to one or more necessary components. In recent years, new methods for preparation of ordered nanostructured materials have become available. We are developing such three-dimensionally designed electrodes which use much smaller amounts and achieve 100% utilization of the catalyst.

Nanofabrication

Materials and devices with nanometer-sized components are foreseen to revolutionize all aspects of human life: from computers to cancer therapy and beyond. A few interesting applications have already emerged, particularly in the semiconductor and biotechnology industries. Fabrication of such small structures is, however, a daunting problem since only a handful of useful techniques are available. We are developing new procedures for high throughput manufacturing of nanodevices.

In the first method, classified as a top-down approach because it starts with a macroscopic object and scales it down, we use electrochemical nanomachining to produce patterns of trenches and vias on a flat surface. This technique has potentially a much higher speed than more commonly studied Scanning Probe Lithography and can be easily applied to making three-dimensional structures.

Another method, a bottom-up approach, relies on a long-range, self-assembling behavior of nanoparticles in electric field in liquids. This phenomenon may open a way to sublithographic patterned assembly, which means fabrication in the nanometer scale using much larger patterns produced by fast and inexpensive conventional lithography.

Selected Publications

1. Timofeeva, E. V., Gavrilov, A. N., McCloskey, J. M., Tolmachev, Y. V., Sprunt, S., Lopatina, L. M. & Selinger, J. V. Thermal conductivity and particle agglomeration in alumina nanofluids: experiment and theory. Physical Review E: Statistical, Nonlinear, and Soft Matter Physics 76, 061203/1-061203/16 2007.

2. Tolmachev, Y. V. & Scherson, D. A. The electrochemistry of sulfite in aqueous solutions: UV-visible reflectance spectroscopy studies at rotating disk electrodes. Proceedings - Electrochemical Society 2003-30, 217-229 2005.

3. Sapozhnikov, M. V., Aranson, I. S., Kwok, W. K. & Tolmachev, Y. V. Self-assembly and vortices formed by microparticles in weak electrolytes. Physical Review Letters 93 2004.

4. Tolmachev, Y.V., A. Menzel, A. Tkachuk, Y. Chu, and H. You. In Situ X-ray Surface Scattering Observation of Long-rang-ordered (√19x√19)R23.4^o-13CO Structure on Pt(111) in Aqueous Electrolytes. Electrochem. Solid-State Lett., 2003.

5. Rhee, C.K., M. Wakisaka, Y. Tolmachev, C. Johnston, R. Haasch, K. Attenkofer, G.Q. Lu, H. You, and A. Wieckowski. Osmium Nanoislands Spontaneously Deposited on a Pt(111) Electrode: The XPS, STM and GIF-XAS Study. J. Electroanal. Chem., 2003.

6. Lister, T.E., Y.V. Tolmachev, Y. Chu, W.G. Cullen, H. You, R. Yoncon and Z. Nagy. Cathodic Activation of RuO₂ Single Crystal Surfaces for Hydrogen-Evolution Reaction. J. Electroanal. Chem., 2003.

7. Sapozhnikov, M.V., Y.V. Tolmachev, I.S. Aronson, and W.-K. Kwak. Dynamic Self-assembly and Patterns in Electrostatically Driven Granular Media. Phys. Rev. Lett., 90, 2003, 114301.

Last Updated: 15 August 2008