(5dd) Thermal and Electrochemical Activation in Hydrogen Production for Fuel Cell Applications

Low temperature fuel cells such as the proton-exchange-membrane (PEM) fuel cells operate well only with rather very pure hydrogen. This is a very big problem, since hydrogen, although very abundant, naturally occurs on earth only in a combined form. Industrially, hydrogen is produced in large quantities from the steam reforming of hydrocarbons. The hydrogen can, of course, eventually be produced from renewable fuels, nuclear energy, wind, or directly from solar energy. In other words, the environmental impact of hydrogen economy is expected to be far less than that of the current fossil fuel based economy, and is the main driving force. The eventual goal is of course to eliminate the use of fossil fuels all together. With hydrogen economy envisioned for automobiles, it is pivotal that technical challenges for widespread production and distribution of hydrogen be thoroughly probed into. Thus, processes for clean hydrogen production need to be rigorously investigated, both mechanistically and kinetically.

With the advent of user-friendly quantum mechanics software, theoretical study of molecular catalytic reaction mechanisms has become rather commonplace as a very insightful tool. The density functional method (DFT) is an inimitable tool for determining the reaction intermediates and building a detailed molecular mechanism for catalytic reactions. However, this is only the starting point for developing a complete understanding of a catalytic system, including the most favorable reaction pathway and the key reaction steps. What is needed is an easy to use addendum to the quantum mechanical software that can utilize its first principles predictions to construct a comprehensive picture of the catalytic system, including elucidation of all parallel pathways and the dominant reaction routes and steps. While software tools such as CHEMKIN are available for this purpose, they are based on rather brute-force numerical methodologies. A more insightful graphic approach is called for that might be readily utilized by the catalytic scientist, without the necessity of being fully conversant with its theoretical underpinnings. Such a consistent graph-theoretic approach will be presented with the focus on H2 production, e.g. steam reforming of methane, methanol decomposition, NH3 decomposition, water-gas-shift reaction (WGSR).

The overall approach involves the following steps: 1) determination of surface intermediates on a given catalyst; 2) generation of a set of plausible surface elementary reaction steps involved in the overall reaction (OR); 3) graph-theoretic generation of a reaction network that depicts the overall mechanism as well as the multitude of reaction routes (RRs); 4) prediction of pre-exponential factors and activation energies, from which energy diagrams are drawn; 5) conversion of the reaction network into an equivalent electrical network that, not only pictorially represents the ?circuitry? of reaction pathways, but also allows rigorous flux and kinetic analysis by making use of the vast array of tools available for the analysis of electrical circuits, namely Kirchhoff's current and potential law. Furthermore, the reaction circuitry allows a reduction of the network by a direct and transparent comparison of the reaction step resistances. Moreover, the rate-limiting steps are identified without any ad hoc assumptions.

A major technical barrier for the application of fuel cells for automobiles is the lack of H2 distribution and storage infrastructure. On board reforming of H2 seems to be viable option, with steam reforming constituting a major source. However, CO present in the reformate poisons platinum electro-catalyst and adversely affects the fuel cell performance, which calls for efficient cleanup processes that are easily integrable with the fuel cells. An entirely novel approach involving electrochemical preferential oxidation (ECPrOx) is being developed in our laboratory, where CO electro-oxidation is achieved at the anode by rendering the process electrochemical. In addition, supplemental power is produced with no hydrogen wasted. The electrochemical enhancement of catalytic WGSR is achieved since the rate of an electrochemical reaction is not only determined by temperature, pressure, and composition, but also by the electrode potential. Moreover, the equilibrium constant of an electrocatalytic reaction is a strong function of potential. Hence both, the thermodynamics and kinetics of WGSR can be improved, if carried out electrochemically. The electrochemical device has direct application in on-board reforming process for fuel cell applications and the potential to replace both WGSR and PrOx. The details of the process will be discussed in the poster presentation.

Research Interests: Fuel cells, Fuel reforming and processing, Heterogeneous catalysis and kinetics, Graph theory

My teaching styles and philosophy are mostly based on the experiences that I have had as a student in a variety of different educational settings. Having engaged classes as a Teaching Assistant at Worcester Polytechnic Institute, I have realized that involving students with the lectures through the use of examples, inquiries, demonstrations and group activities provides a more amiable atmosphere in which the students and instructors gain immediate feedback on student comprehension when compared to strictly lecture-style classes.

My strong interest in both research and teaching are further fortified by winning campus and national awards in research (CRE Division's Best Poster Award, AIChE 2007 and Graduate Research award, Worcester Polytechnic Institute, 2007-2008) and teaching (Teaching Assistant of the year award, Worcester Polytechnic Institute, 2008).