The rapid depletion of fossil fuels and growing environmental concerns have created enormous worldwide demand for alternative, clean energy technologies. Energy is the single greatest challenge facing humankind in the 21st century. Fuel cells offer tremendous promise for solving a variety of energy needs ranging from portable to automobile to stationary power, reducing our global dependence on oil and fostering future energy security, prosperity, and a cleaner environment. However, fuel cell technologies are confronted with numerous materials challenges associated with durability, performance, and cost, impeding the commercialization prospects. As evident from the 2004 National Research Council/National Academy of Engineering report and the American Physical Society report, a profound fundamental understanding of the chemical and physical processes in fuel cell materials is vital for enabling significant breakthroughs that will lead to enhanced fuel cell performance at an affordable cost. For example, the high cost and limited abundance of the currently used platinum catalysts pose serious problems for the commercialization prospects of fuel cells. This proposal addresses this critical issue by exploring new palladium-based alloy catalysts; the cost of palladium is one-fifth of the cost of platinum. Nanostructured palladium-based alloy catalysts for oxygen reduction reaction (ORR) are designed based on a guiding principle involving the pairing of a good oxygen-bond cleaving metal such as Co for first splitting the O-O bond to form adsorbed oxygen with a good oxygen-reduction metal such as Pd for efficiently reducing the adsorbed oxygen atoms to oxide ions. Potential catalyst compositions are identified by a cyclic voltammetric (CV) screening with glassy carbon microelectrodes. Multi-metallic binary and ternary alloy compositions consisting of palladium and other metals like Ti, V, Cr, Fe, Co, Ni, Cu, Mo, W, Ru, Au, and Pt are synthesized by novel low temperature approaches such as a reverse microemulsion method employing different reducing agents like sodium formate or sodium borohydride and polyol reduction methods, followed by heat treatment at moderate temperatures to achieve a high degree of alloying and homogeneity, small and uniform distribution of particle size, high catalytic activity, and good chemical stability. The alloy catalysts are characterized by a variety of physical techniques including diffraction, microscopy, spectroscopy, and electrochemical measurements (cyclic voltammetry, linear polarization, and rotating disk electrode methods). The catalytic activity is evaluated for both oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) in single cell proton exchange membrane fuel cells and direct methanol fuel cells with hydrogen and methanol fuels. Based on the results, a fundamental understanding of the catalytic mechanisms is developed.
Intellectual Merit: The intellectual merit of the proposed activity is to (i) develop a basic scientific understanding of the factors that control the electrocatalytic activity of nanostructured palladium-based alloy catalysts for oxygen reduction reaction and methanol oxidation reaction in fuel cells, and (ii) utilize the knowledge to design and develop new less expensive, more efficient palladium-based catalysts for fuel cells. Palladium-based alloy catalysts designed with a guiding principle are synthesized by controlled, low temperature methods to keep the particle size small and maximize the catalytic activity, screened with cyclic voltammetry, and characterized by a variety of physical, chemical, and electrochemical techniques to establish the catalytic mechanisms involved. The proposed research activity will enhance our fundamental understanding of the structure-property-performance relationships of electrocatalysts and the commercialization prospects of fuel cell technology.
Broader Impact: The proposed research provides a broader interdisciplinary training to students in a unique, nationally important area of materials for energy conversion, encompassing materials chemistry and electrochemical science and engineering. The realization of a strong scientific basis in this area can help to design and develop new materials for power sources for portable, automobile, and stationary applications, which would have a profound societal impact. The proposed activity also aims to recruit and train minority and women students and educate K-12 students and the general public about clean energy technologies and materials.
