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Water ionization


Research Overview

The UW Electrochemical Surface Science (UWESS) group examines surface science phenomena related to electrochemical situations, with an emphasis on fuel cells and related technologies. Current projects include electrochemical reforming of biomass to hydrogen, density functional theory of water adsorption and diffusion, the role of electric field in water ionization and surface reactions, and oxidation reactions in hydrocarbon-fueled solid oxide fuel cells.

Stuve photo

Eric M. Stuve
Professor of Chemical Engineering
University of Washington

206-543-0156
stuve@uw.edu
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Electrocatalytic Reforming of Biomass for Hydrogen Production
Concerns about a finite energy supply, geopolitical issues, and environmental impact of fossil fuels motivate research in biofuel production. Biomass is an abundant resource, but not easily converted to a usable transportation fuel.

Hydrogen production is one of the key processes in a refinery, important for liquid fuel production and in fuel cells. Electrocatalytic reforming of biomass is an attractive option for hydrogen production, as it naturally separates hydrogen and offers greater control of the reaction. We are examining this process by reforming of ethylene glycol, the simplest sugar:


Anode: C2H6O2 + 2 H2O  —>  2 CO2 + 10 H+ + 10 e

Cathode: 2 H+ + 2 e —> H2

Successful electrocatalytic reforming requires effective electrooxidation, which typically is hampered by formation of poisons at the anode, and the motivation of this work is to find conditions favor reaction.

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ECR
                                Biomass
Adsorption and Diffusion of Water
A general phenomenon in the study of surface science involves adsorption systems with similar substrate--adsorbate (SA) and adsorbate--adsorbate (AA) interactions, exemplified by water adsorption on late transition metals.  We have examined water adsorption and diffusion on Pt(111) terrraces and stepped and kinked Pt sites for Pt-water adsorption energies, hydrogen bonding among adsorbed water molecules, and diffusion pathways of both monomeric and polymeric water species, and activation energies of diffusion.  These studies also show how water wets a Pt surface: water diffuses from terrace sites, to step sites, and to kink sites.  With varying diffusion activation energies throughout the process.

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Water diffusion pathways

Field Ionization of Water

Considered at the molecular level, water at a metal surface exists in an extreme environment for, in addition to the balance of forces between chemisorption and hydrogen bonding, there exists an electric field on the order of several V/Å. Fields of this magnitude distort molecules, induce ionization, and break bonds, and thus play a central role in interfacial water chemistry. As examples, self-ionization of water,

       (H2O)m+n+1 —> (H2O)mH+ + (H2O)nOH,

the foundation of nearly all aqueous chemistry, is itself field dependent, and the orientation of adsorbed water in an electrochemical environment is affected by electric field. This work examines the ways in which surface electric fields affect water, its ionization, and surface reactions from the standpoint of electrode/electrolyte interfacial chemistry.

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Proton desorption

Oxidation of Hydrocarbon Fuels at Solid Oxide Anodes

Solid oxide fuel cells (SOFC) provide an opportunity for fuel-flexible fuel cells that operate at higher efficiencies than other types of fuel cells. Some of the issues faced in direct hydrocarbon oxidation are: (1) avoiding carbon formation on the anode and (2) understanding the role of oxide ions in the reaction mechanism. To address these issues we have developed measurements that highlight the interplay of fuel oxidation kinetics, carbon deposition on the anode, and transport of oxide ions through the electrolyte. Results, obtained for a number of different fuels show some fascinating behaviors, including induction periods for electrocatalytic oxidation, spontaneous and forced oscillations, and coupled reforming with direct surface reaction.  The overall implication is that catalyst activity is a strong function of electrolyte structure, ionic flux, and adsorption kinetics of the fuel. This work was funded by the Office of Naval Research.

ATRP model
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Energy Facts and Figures

This one-page article summarizes topics covered in the Energy and Environment course (CHEM E/ ENVIR / M E 341, Autumn 2012). It can be used as is or printed out and pasted onto two double-sided 3 1/2 x 5 inch cards or four single-sided cards. This material is for informational, instructional, or preliminary design purposes. Because of approximations used in presenting data, this sheet should not be used for process or equipment design beyond the preliminary stage.






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Energy Facts and Figures
Fuel Cell Engineering

The Fuel Cell Engineering course (CHEM E 445) gives students an in-depth exposure to science and technology of fuel cells.  By comparative study of proton exchange membrane (PEM) and solid oxide fuel cells (SOFC), students learn the underlying fundamentals of these two technologies, assessment of their performance, and how to match fuel cells to their intended application.  More than 300 UW students and 100 off-campus students have taken this course since its introduction in 1996.








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PEM
                                processes
Logarithmic Error Bars

The "log error bars" article has proven popular over time and is included here to help those who would like to calculate and display error bars properly on logarithmic plots. It has recently been updated to improve clarity and provide reference information.





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Log-Error
                                Plot
Fuel Cell Symbol

A fuel cell combines chemical and electrical engineering in one unit.  It is inherently a complex device requiring special considerations both chemically and electrically.  The symbol at right provides a convenient means for representing a fuel cell in combined chemical process and electrical circuit diagrams and for either diagram separately.

Fuel
                                cell symbol
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