The objective of this project is to study fundamental catalytic mechanisms of nitrogen-doped carbon nanomaterials as high-performance catalysts for fuel cells. Fuel cells convert chemical energy directly into electricity by oxidizing, for example, hydrogen gas at the anode and reducing oxygen gas at the cathode. The relatively slow oxygen reduction reaction on the platinum cathode is a key step to limit the energy conversion efficiency of a fuel cell, and the high cost of the platinum catalysts has also been shown to be the major "showstopper" to mass market fuel cells. This project will focus on the development of new forms of nitrogen-doped carbon nanomaterials as low-cost, metal-free, efficient catalysts for oxygen reduction. A unique approach will be developed to experimentally study the molecular structures and catalytic activities of the new materials, in conjunction with an atomistic modeling of such structures to link the nanoscale phenomena to macroscopic catalytic performance and to evaluate the oxygen reduction reaction mechanism for highly-efficient, low-cost energy conversion in fuel cells.
The knowledge acquired will lead to not only a strong fundamental understanding of new scientific principles for the oxygen reduction reaction, but also developing/optimizing the nitrogen-doped carbon nanomaterials for fuel cell applications, even as new catalytic materials for applications beyond fuel cells. This project will benefit in developing new catalytic materials and energy devices for a broad range of applications in the field of clean energy conversion technologies (e.g. fuel cells, batteries, solar cells), chemical and materials engineering (e.g. corrosion, material synthesis), and biological and environmental engineering (e.g. biosensors, chemical sensors). The education impact will be to create an environment where all-level students (graduate, undergraduate, high school, and students from underrepresented groups) from multidisciplinary background work together on the development of a common platform. The research experience will be incorporated in interdisciplinary classes taught at CWRU (Electrochemistry, Nanotechnology) and Akron (Multiscale Modeling).
As originally proposed, we have focused on the fundamental study on catalytic mechanisms of nitrogen-doped carbon nanomaterials to develop new design concepts of manufacturing high-performance catalysts for fuel cells. More specifically, we have studied the electrocatalytical mechanism of nitrogen-doped graphene in acidic environment by using the density function theory (DFT). Several models for graphene and carbon nanotubes with or without nitrogen doping were built to identity the oxygen reduction reaction (ORR) pathway and active sites. The energy for each reaction step was calculated. The spin density and atomic charge density were also calculated. The ORR mechanisms were analyzed in details based on the information obtained from the modeling. Insights gained from these theoretical studies have been used as guidance for the design and development of new concepts of manufacturing high-performance catalysts for fuel cells. As a result, we have for the first time developed a simple plasma-etching technology to effectively generate metal-free particle catalysts for efficient metal-free growth of undoped and/or nitrogen-doped single walled carbon nanotubes (CNTs) as metal-free catalysts with a relatively good electrocatalytic activity and long-term stability towards ORR in acidic medium. Nitrogen and other dopant elements, as well as defects, were also introduced into graphene structures. We have also successfully developed PDDA-functionalized/adsorbed graphene as metal-free catalysts toward ORR in fuel cells with similar performance as Pt catalysts. Nitrogen-doped oxygen-rich graphene quantum dots (GQD) have been prepared by either electrochemical oxidation or solution synthesis while edge-sulfurized graphene nanoplatelets (SGnP) were prepared by simply ball-milling the pristine graphite in the presence of sulfur (S8). The ORR electrocatalytic activities in alkaline medium were evaluated for both the GQD and SGnP. On the basis of these theoretical and experimental studies, we have published about 20 journal publications, including Acc. Chem. Res., Adv. Mater., JACS, ACS Nano, and Small papers. Our work has also received numerous commentaries appeared in scientific, business, and popular press (please see: "Events & News" at http://case.edu/cse/eche/daigroup/index.html). This project has led to not only a strong fundamental understanding of new scientific principles for the oxygen reduction reaction, but also innovative approaches to new catalytic materials and energy devices for a broad range of applications in the field of clean energy conversion technologies (e.g. fuel cells, batteries, solar cells), chemical and materials engineering (e.g. corrosion, material synthesis), and biological and environmental engineering (e.g. biosensors, chemical sensors). The education impact includes the creation of an environment where all-level students (graduate, undergraduate, high school, and students from underrepresented groups) from multidisciplinary background work together on the development of a common platform. A special effort has been made to encourage participation of student(s) from under-represented groups. Indeed, three undergraduate students have actively participated in our research on the part-time basis. One PhD student has successfully graduated from CWRU in May, 2013.