Solid oxide fuel cells (SOFCs) are devices that convert chemical energy of combustible fuels into electricity. Important components of solid oxide fuel cells (SOFC) are electrodes (anode and cathode) which activate electrochemical catalytic reactions. Even though, SOFCs are very promising devices, it is astonishing how little is known about the underlying mechanisms of electrochemical reactions that govern the performance of the SOFC electrodes. For example, even for a conceptually very simple H2-oxidation reaction (H2 + O2- = H2O + 2e-) at the SOFC anode, there exist a large number of mutually conflicting elementary step mechanisms that have been proposed based on various experiments. Recent review papers in the field as well as the reports of various scientific advisory committees have emphasized the need for a better molecular level understanding of electrochemical reactions at interfaces of solid electrodes and solid electrolytes.
This project will employ quantum Density Functional Theory (DFT) calculations to study elementary step mechanisms of electro-catalytic oxidation reactions over solid oxide fuel cell (SOFC) anodes. We will employ realistic model systems that account for the presence of the metal/electrolyte interface. Potential bias and electric field effects will be incorporated in our first principles calculations. While we focus on SOFC anodes, the proposed methodology is universal and it can be easily employed to address other electro-catalytic systems where solid-state electrochemistry plays a role, such as solid-state sensors, microelectronic devices, solid-state batteries, and many others. We note that the methodology outlined in this proposal has not been utilized previously to study solid-state electrochemistry.
The central objective is to aid the development of predictive molecular theories aimed towards the discovery of novel SOFC material. To accomplish these objectives, we have identified four major goals: (1) we will develop a very general methodology that will allow us to study heterogeneous electro-catalytic reaction from first principles, (2) we will asses the thermodynamic feasibility of multiple elementary step mechanisms that have been proposed based on the previous experimental studies of SOFC anodes, (3) we will investigate the kinetics of the various proposed mechanisms by integrating the elementary step information into micro-kinetic models, (4) we will integrate the approach in our educational activities via multiple outreach activities and a new course development.
The focus is on the theoretical studies since the solid-state electrochemical reactions are difficult to probe experimentally. The difficulties stem from: (i) an inherent experimental inaccessibility of the catalytically important metal/electrolyte interface sites, (ii) high electric fields, (iii) high potential bias, and (iii) high temperatures at which these reactions take place. The proposed theoretical framework will address these issues. We have already performed significant preliminary work demonstrating the usefulness of the proposed approach.
Our central educational objective is to promote molecular approach to energy related science and technology. The educational objectives will be addressed via multiple outreach activities and the integration of the material into the curriculum. For example our group will participate in the Detroit Area Pre-College Engineering Program (DAPCEP) which offers free engineering classes to students in grades 7 and 8 from the Detroit area and the NASA Summer High School Appreciation Program (SHARP) which aims to introduce high school students (grade 10 and 11) to active scientific research.
The concepts proposed in this research project will also be integrated into the curriculum by introducing a cluster of courses related to energy and sustainability. This will be taught by a number of faculty members, including the PI, in the department. Furthermore, graduate students who are directly involved in the research program will be exposed to a comprehensive set of theoretical and experimental tools that will allow them to tackle most of the relevant electro-catalysis issues. In addition, we will design an educational module that will be annually presented to large groups of high school students that visit the U of Michigan during summer months. In our laboratory, we also have a three months long research internship that we offer to a promising high school student.
Solid oxide fuel cells (SOFCs) are devices that convert chemical energy of combustible fuels into electricity. Important components of solid oxide fuel cells (SOFC) are electrodes (anode and cathode) which activate electrochemical catalytic reactions. Even though, SOFCs are very promising devices, it is astonishing how little is known about the underlying mechanisms of electrochemical reactions that govern the performance of the SOFC electrodes. We began this project in 2009 by attempting to develop quantum Density Functional Theory (DFT) framework that would allow us to study elementary step mechanisms of electro-catalytic oxidation reactions over solid oxide fuel cell (SOFC) electrodes. The models we developed in the first two years have allowed us to account for the critical features of an electrochemical system, i.e., the presence of the metal/electrolyte interface, potential bias and electric field. We have used these first principles DFT approaches to address a number of practical issues including the discovery of new anode electro-catalysts that are more resistant to carbon-induced deactivation than conventional electro-catalysts in electrochemical oxidation of hydrocarbons over SOFC devices. The superior performance of the alloy electro-catalysts was demonstrated experimentally in our laboratory by testing the alloy materials against the conventional electrocatalysts in an SOFC test station. More recently, we have expanded the use to the techniques developed under this grant to study other relevant electrochemical reactions, most notably electro-chemical oxygen reduction reaction (ORR) on Pt and Pt alloys. This work has led us to shed light on a number of unresolved issues related to this reaction. In particular, we have been able to identify the molecular origin of potential-induced shift in the magnitude of Tofel slope for ORR on Pt. Conventional electro-chemical theories do not predict such a shift. The molecular understanding of ORR that emerged from these studies allowed us to identify the critical molecular descriptors of electro-chemical activity leading us to new potentially more promising materials than pure Pt for ORR. Our central educational objective is to promote molecular approach to energy-related science and technology. We have been addressing this educational educational objectives via multiple outreach activities and the integration of the material into the curriculum. For example our group participates in the Detroit Area Pre-College Engineering Program (DAPCEP) which offered free engineering classes to students in grades 7 and8 from the Detroit area. We have also developed a course focusing on molecular analysis of heterogeneous catalysis and electro-catalysis. The course has been taught twice with a very high degree if interest from chemical engineering students at U of Michigan. Main Findings: We have developed a very general approach that allows us to study elementary electro-chemical transformations from first principles. We have used the first principles approach to investigate the electrochemical oxidation of hydrogen on different surface of various transition metals. These studies shed light on the mechanisms of the H2 electro-oxidation on Solid Oxide Fuel Cells. :(J. Mukherjee, S. Linic, 'First principles investigations of electrochemical oxidation of hydrogen at solid oxide fuel cell operating conditions', Journal of the Electrochemical Society, 154(9), B919-B924, 2007) We have expanded the approach to study electro-chemical oxidation of various hydrocarbons on different metallic anode electro-catalysts. This work identified the underlying molecular features of the electro-catalyst that govern its performance. ( 'D. B. Ingram, S. Linic, J. Electrochem. Soc., 156,B1457, 2009) Another critical problem with conventional Ni SOFC anodes is that when exposed to hydrocarbon, in the process of direct electro chemical oxidation on SOFCs, they deactivate due to the buildup of carbon deposit on the surface on Ni. We have studied the process of the formation of solid carbon species on Ni developing underlying mechanism that governs this process. This molecular information was used in quantum chemical calculations to identify Ni-alloys (mainly Ni/Sn, Ni/Ag, and Ni/Au) that are much more resistant to carbon than conventional Ni anodes. Subsequent experimental test supported these findings demonstrating that these NI alloys are much more robust than Ni in direct electro-chemical oxidation of hydrocarbon fuels, including methane, propane, and oso-octane. This work has led to an interest by an SOFC producing company (AMI) which is interested in the commercialization of this technology. We have expanded the use to the methodology to study other relevant electrochemical reactions, including electro-chemical oxygen reduction reaction (ORR) on Pt and Pt alloys. This work has shed light on a number of unresolved issues related to this reaction. We have been able to identify the molecular origin of potential-induced shift in the magnitude of Tofel slope for ORR on Pt. Conventional electro-chemical theories do not predict such a shift. ( A. Holewinski, S. Linic, J. Electrochem. Soc., 2012) The molecular understanding of ORR that emerged from these studies allowed us to identify the critical molecular descriptors of electro-chemical activity leading us to new potentially more promising materials than pure Pt for ORR
