(7em) Explaining Surface-Catalyzed Reactions in Electrochemistry | AIChE

(7em) Explaining Surface-Catalyzed Reactions in Electrochemistry


Walker, E. - Presenter, University of Michigan

Research Interests:

Electrochemical surface-catalyzed reactions provide potent
chemical tranformations which are promising to enable an alternative energy future.  One quintessential electrochemical
surface-catalyzed reaction is carbon dioxide reduction.  Essentially, this reaction can close the
carbon cycle because the carbon from carbon dioxide is passed to carbon-containing
fuels.  High-performance computing
will continue to provide insight into the atomistic scale reaction mechanism,
which is poorly understood.  Reaction
mechanisms studies have initiated, but many reaction pathways remain unknown.1,2  The
reaction occurs with a catalyst surface which experiences electrical
charge.  Recently3,
as many as sixteen chemical products of this reaction have been measured.  The number of surface reactions is large
and obtaining the most accurate transition states for each reaction can make a
difference in which is the dominant reaction mechanism.  Furthermore, a change in a transition
state can influence the rate-controlling step.4  To face this challenge, the
growing string method is able to automatically search for reaction paths of
elementary steps and their contained transition states in a rapid manner.5  This automated reaction path discovery
may be initiated from an initial geometry-optimized reactant and driving
coordinates including bond breaks, bond additions and/or bond torsions.

Continuum-scale modeling, orders of magnitude longer length
and time scales than atomic-scale density functional theory modeling, can offer
the most realistic predictions of reaction performance.  Continuum-scale modeling incorporates
non-idealities such as concentration and pH gradients.  For example, the pH of the layer of
solvent near the surface of a copper catalyst changes in pH which affects the
solubility of CO2.6  CO2 must migrate to
the catalyst surface for the reaction to activate.  Also, the pH of the solvent region near
the catalyst may be considered to drive reactions in the solvent, absent the catalyst.7  Transferring
uncertainty from ab initio calculations to the
reactor-scale continuum offers a challenge to incorporate all uncertainties and
non-idealities.8 Figure 1 displays the length and time scales
bridged by a multi-scale model.  All
together, this careful multiscale modeling of the
electrochemical reduction of carbon dioxide will advance understanding of its
mechanism and enable the improvement of the reaction performance. 

Teaching Interests:

For teaching undergraduate courses,
I am particularly interested in: Numerical Methods for Chemical Engineers, Mass
and Heat Transfer, and Chemical Engineering Kinetics.  For teaching graduate courses, I am
interested in courses such as Chemical Reactor Design and Chemical Process
Principles. In any course I teach, the incorporation of computer programming would
ensure that students learn attention to detail and how to formulate engineering
problems in an explicit manner.  Furthermore,
I believe visualizing data and technical writing are skills that chemical
engineers should obtain in preparation for the labor force or academia.

Figure 1.  Length and time scales of density functional theory to chemical
reactor modeling.

[1] Goodpaster, J. D.; Bell, A. T.;
Head-Gordon, M. Phys. Chem. Lett. 7
(2016) 1471-1477.

[2] Gattrell, M.; Gupta, N.; Co, A. J. Electroanal.
Chem. 594 (2006)

[3] Kuhl, K. P.; Cave, E. R.; Abram, D. N.; Jaramillo, T. F. Energy Environ. Sci. 5 (2012) 7050-7059.

[4] Jorgensen, M.; Gronbeck,
H. ACS Catal.
6 (2016) 6730.

[5] Jafari, M.; Zimmerman, P. M. J.
Chem. 38 (2017)

[6] Singh, M. R.; Kwon, Y.; Lum,
Y.; Ager, J. W.; Bell, A. T. J. Am. Chem. Soc. 138 (2016) 13006-13012.

[7] Birdja, Y. Y.; Koper, M. T. M. J. Am. Chem. Soc. 139 (2017) 2030-2040.

[8] Tinsley Oden, J.; Prudhomme,
S.; Romkes, A.; Bauman. P. T. SIAM J. Sci. Comput.
28 (2006) 2359-2389.