Intellectual Merit: The objective of this research is to develop a new methodology for understanding the mechanisms of electro-catalytic conversions of highly functionalized organic compounds in aqueous phase systems. To that end, a powerful in situ technique, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, will be integrated into the design of an innovative "spectro-electrochemical cell". This device will be used to study solution/electrode interfaces systematically (e.g., as a function of electrode potential, solution pH, and surface functionality). Model organic compounds with key chemical functional groups will be used as probes for elucidating catalytic charge transfer mechanisms, primarily under reductive (cathodic) conditions. Additionally, a series of batch-reaction experiments will be performed in parallel to determine the kinetics of these reductive conversions, including measurements as a function of temperature for determination of activation energies. The experimental data will be complemented with density functional theory (DFT) calculations to augment and validate the mechanistic insights. The combination of in situ ATR-FTIR spectroscopy, kinetic measurements, and DFT calculations will constitute a new methodology for developing a deeper understanding of the mechanisms of electrochemical reactions in aqueous solutions.
This new methodology will be demonstrated using conductive boron-doped diamond (BDD) film electrodes. The main advantages of BDD electrodes over traditional glassy carbon, noble metal, and metal oxide electrodes are: 1) high stability under anodic polarization, 2) suppression of water electrolysis reactions, 3) chemical inertness, and 4) low background current and double layer charging. These properties also make BDD films an ideal support for studying the catalytic and electrochemical properties of metal nanoparticles. Although research on BDD electrodes has increased in recent years, a mechanistic understanding of the surface chemistry of the BDD surface and supported metal nanoparticles under in situ conditions has not been developed. The surface chemistry of the BDD surface can change depending on the applied electrode potential and solution conditions and is the governing factor for charge transfer at the solution/electrode interface. These factors dictate the utility of BDD electrodes for a vast number of applications.
Broader Impact: BDD electrodes have been successfully shown to have a variety of technological applications: 1) water disinfection and treatment; 2) electrochemical sensing; and 3) electro-synthesis of organic compounds. Their potential use as catalyst supports remains largely untapped, although their application is highly attractive for systems that may involve aqueous environments such as bio-feedstock processing for fuels or "green chemistry" for specialty chemicals production.
This project will also increase participation of graduate and undergraduate students from underrepresented groups in engineering research. The graduate students will participate in the Alfred P. Sloan Foundation: American Indian Graduate Partnership Fellowships and Arizona Scholars Program. This program is designed to address the national need for academically - prepared Native Americans who can help spur economic development in their communities and reservations and occupy leadership positions in colleges and universities, government and the corporate world. The project will also provide new expanded opportunities to involve high school and undergraduates in research through the UA Professional Internship Program for High School Seniors, the NASA Space Grant Undergraduate Internship Program, the UA Water Sustainability Undergraduate Fellowship Program, and the UA Summer Research Institute (SRI). The Chemical and Environmental Engineering Department is currently the host for an NSF REU and RET site on "Systems Approach to Sustainability: Manufacturing, Water and Energy" (NSF# 0649202). The proposed research will involve several undergraduates and high school teachers from these programs during each year of the grant.
Overview: The goals of this project were to develop a new methodology for understanding electrochemical reactions that occur on electrode surfaces and to train a broad group of students in the fields of Chemical/Environmental Engineering. The specific project outcomes that were achieved during the life of this project are described below in the context of Intellectual Merit (i.e., intellectual contributions to the field) and Broader Impacts to society at large. Intellectual Merit: The outcomes from this work have resulted in the publication of three manuscripts in top tier peer-reviewed journals and several conference presentations and invited talks. Other manuscripts will be submitted to peer-reviewed journals in the coming months. The body of knowledge generated from this project has allowed us to develop a powerful new methodology for understanding the mechanisms of electro-catalytic conversions of compounds in aqueous phase systems. Specifically, we have focused on the reactions that occur during the electrochemical production of hypochlorite (i.e., bleach), and have gained a thorough understanding of the reactions that cause unwanted byproducts (e.g., chlorate, perchlorate) during this process. Our most important contribution to the field is the development of a novel methodology that uses experimental data and theoretical calculations to understand complex electrochemical reactions. Broader Impact: The outcomes of this work have resulted in several broader impacts to both the scientific community and society at large. The intellectual outcomes, discussed above, are beneficial to electrode manufacturers, and can be used to develop materials that are more selective for target reactions. Electrodes are being used in a wide-range of technologies, which include batteries, sensors, fuel cells, and water treatment, and therefore research in these areas can benefit from our work. The project has also resulted in the training of a broad group of students; many of these students are from underrepresented groups in science and technology. This project has allowed one student to obtain his Ph.D. and one female, minority student to obtain her Master’s degree. Several undergraduate students have also had the opportunity to conduct research on this project, as part of our outreach efforts. Our education/outreach plan has also resulted in the development of educational modules related to the intellectual outcomes of this work. These educational modules have been instituted into undergraduate/graduate curriculum and middle school outreach programs, and thus have promoted the training and development of a broad group of students.
