MSE Colloquium - Prof. Kwong-Yu Chan
Date: October 26, 2012 from 2:00 pm to 3:00 pm EDT
Location: Room 214, S. W. Mudd
Contact: For further information regarding this event, please contact Wesley Hattan by sending email to wjh2121@columbia.edu or by calling 2128547860.
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Energy Conversion in Well-defined Mesoporous Electrodes

Kwong-Yu CHAN

Department of Chemistry

The University of Hong Kong

Energy conversion devices of fuel cells and super-capacitors have electrochemical processes taking place in porous electrodes. Optimization in multiple length scales in terms of composition and structure of the electrode is needed to provide high surface area for reaction while maintaining efficient transport of ions, electrons, reactants, and products. There is also increased attention to utilization of precious metals and durability. The issues are discussed through experimental studies of a set of well-defined hollow core-mesoporous shell (HCMS) structures.

The 3-D hierarchical HCMS carbon structure has an assembly of spherical carbon particles each with a hollow core surrounded by a shell which contains mesopores of 3.9 nm [1]. The series of mesoporous shell structures has thickness stepwise increased from 0, 25, 50 to 100 nm while keeping an identical 330 nm hollow core. A systematic investigation of electrochemical capacitance and ionic transport is enabled. A thicker shell has a higher surface area with a proportional increase of electrochemical capacitance which however, can only be fully realized at low scan rates/currents. At high currents, ionic transport limits the electrochemical capacitance of a thick mesoporous shell. Electrochemical impedance spectroscopy (EIS) performed on the family of shell HCMS carbon structures reveals the need to match penetrating and frequency for optimum power with a characteristic time constant for a given structure.

In fuel cells, effective utilization and stability of precious metal is necessary for commercial considerations. The distribution of Pt and PtRu nanoparticles in a mesoporous carbon can impact on electrode performance.  We synthesis HCMS with Pt particles uniformly dispersed into the mesoporous shell using a previously developed CPDP method [2]. Distributing Pt nanoparticles into a thicker shell does not give better Pt utilization for methanol oxidation. However, the particles dispersed into a thicker shell are more stable and give better performance over time.

[1]. F. Li, M. Morris and K.Y. Chan*, "Electrochemical Capacitance and Ionic Transport in the Mesoporous Shell of a Hierarchical Porous Core-Shell Carbon Structure", J. Mater. Chem. 21 (2011) 8880-8886.

[2] F. Li, K.Y. Chan*, and H. Yung, "Carbonization over PFA-Protected Dispersed Platinum: An Effective Route to Synthesize High Performance Mesoporous-Carbon Supported Platinum", J. Mater. Chem. 21 (2011) 12139-12144.