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Amine promotion of hydrogen evolution reaction suppression and CO2 conversion for artificial photosynthesis

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Title: Amine promotion of hydrogen evolution reaction suppression and CO2 conversion for artificial photosynthesis
Author(s): Zhu, Wei
Director of Research: Masel, Richard I.
Doctoral Committee Chair(s): Masel, Richard I.
Doctoral Committee Member(s): Kenis, Paul J. A.; Gewirth, Andrew A.
Department / Program: Chemical & Biomolecular Engr
Discipline: Chemical Engineering
Degree Granting Institution: University of Illinois at Urbana-Champaign
Degree: Ph.D.
Genre: Dissertation
Subject(s): Amine Hydrogen evolution reaction Carbon dixoide reduction
Abstract: Recycling CO2 back into fuels or other useful products is critically important to the global efforts to reduce greenhouse gases and global warming [1-3]. The electrochemical method is regarded as a promising means to do this because it has the advantage that water can be used as the proton source [4, 5]. However, the overpotential for electrolysis of water is low, whereas the overpotential of electrochemical conversion of CO2 is too high. Increasing the overpotential of water decomposition and lowering the overpotential of CO2 reduction is considered one of the grand challenges for catalysis. Choline based products are chosen as ideal electrolytes to achieve both hydrogen evolution reaction suppression and lowering of CO2 reduction overpotential of. Experiments combining both electrochemical methods and surface enhanced Raman spectroscopy (SERS) techniques obtain a fairly complete picture of hydrogen evolution reaction and CO2 reduction in choline products. Based on the experimental data, we have discovered that if we conduct CO2 reduction in choline based quaternary ammonium salts, the overpotential decreases and the starting potential of hydrogen evolution increases. This can be contributed to the fact that amine from choline based electrolyte initiates the suppression of the hydrogen evolution reaction and also acts like a co-catalyst to stabilize intermediates of CO2 reduction. In particular, we discovered that: 1. Choline based quaternary ammonium salts achieve hydrogen evolution reaction suppression because a thin layer of choline ions forms on the catalyst surface and blocks the protons from getting close to the surface. 2. Different reaction products are forming during CO2 reduction in choline based electrolytes: CO mainly on gold, platinum and platinum/ruthenium; formic acid on palladium. 3. CO2 reduction happens in a variety of catalysts with much lower overpotential because the thin layer of choline ions on the catalyst surface will form lower energy intermediates with CO2, which will make the carbon dioxide reduction process easier. 4. Different anions in choline based electrolytes have little effect on CO2 reduction as well as hydrogen evolution reaction.
Issue Date: 2011-08-25
URI: http://hdl.handle.net/2142/26014
Rights Information: Copyright 2011 Wei Zhu
Date Available in IDEALS: 2011-08-25
Date Deposited: 2011-08
 

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