Despite decades of promise regarding renewable, environmentally safe, and highly efficient power generation, the practical realization of hydrogen and alcohol-powered fuel cells remains elusive. The main reason that the few fuel cell powered vehicles on the road today are heavily subsidized by manufacturers is that a suitable replacement for expensive metal Pt bulk catalyst has yet to be identified. The research effort seeks to minimize the use of Pt by confining it to only the topmost atomic layers where it is actually needed. To achieve this; understanding of how matter transitions from an initial state consisting of clusters of individual metal atoms to the final nanocrystalline state of which catalytically active metals are composed will be developed. New physical properties manifested at this small size range can be harnessed not only for fuel cell electrocatalysis, but for emergent technologies such as redox flow batteries (RFBs) and thermoelectric power generation (TPGs). The educational aspect of this project aims to: (i) Enhance pre-college education and minority outreach via initiatives with local high schools. (ii) Upgrade chemical engineering curriculum with new laboratory modules that integrate recent progress in sustainable energy technology. (iii) Introduce undergraduate cross-disciplinary activities within professional societies (AIChE, ACS).
The primary objective of this research is to develop safe, sustainable, and scalable chemical syntheses that produce metal nanoparticles (NPs) having bismuth as their core component. Bi is an earth-abundant element with low toxicity and water-stability that has yet to be exploited to enhance material durability in clean, efficient power generation. The noble character of Bi makes it an attractive support for precious metal electrocatalysts required for both the oxygen reduction reaction (ORR) and fuel oxidation (hydrogen, alcohol, etc.) in proton exchange membrane fuel cells (PEMFCs). The most efficient use of precious metals in catalysis is achieved by their surface segregation on dispersed NP cores of base metals so as to maximize their surface to volume ratio. Prior attempts in the field to implement this strategy with metals other than Bi (e.g., Ni, Co, and Fe) have failed due to their dissolution in the fuel cell environment. In addition, Bi NP formation has proven difficult due to the use of toxic organic solvents, difficult-to-synthesize organic precursors, and dangerous hydrazine or lithium reducing agents.
In direct contrast to prior results in the field; this research will examine all-aqueous, all-inorganic synthesis processes for the growth of NPs in which SnCl2 is used as a simultaneous surfactant and reducing agent. Bi is well known to be unstable in the high salt, low pH environment required for SnCl3- surfactant formation and therefore, these colloidal synthesis routes are unexpected. Previously, the potential for SnCl3- ligand attachment to Bi has not been recognized. Consequently, our initial successes with Bi-Pt NP synthesis using this unique inorganic ligand approach were very surprising. To more fully understand these phenomena, detailed experimental characterization of the NPs will be conducted using time-resolved, in-situ X-ray and 119Sn Mössbauer spectroscopies to study the kinetics of pure Bi and Bi-alloy NP formation and SnCl3- ligand shell evolution from the initial complex.
