EAGER: Identifying Active Sites in Electrocatalysis by Steady-State Isotope-Transient Technique

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

The project will develop and apply new methods to understand molecular-level processes applicable to the design of catalysts for direct methanol fuel cells (DMFCs). Fuel cells utilizing liquid fuels pose benefits in energy density, safety, and ease of fuel transport and storage. DMFCs, in particular, are attractive because of ready availability of methanol, and the potential for producing methanol from renewable resources. However, the low energy conversion efficiency of current DMFC technology has curtailed widespread use. This work will provide detailed understanding of the catalytic reactions that occur in a DMFC, such that more efficient catalyst materials and structures may be proposed. The methods developed should advance direct methanol fuel cell technology along the path toward broader commercial application, thereby enabling cleaner and more efficient energy production. The project will enable a new method for operando counting of active catalytic sites via the first demonstration of liquid-phase electrochemical steady-state isotope-transient kinetic analysis (SSITKA). The method development will utilize - as a probe system - the electrochemical methanol oxidation reaction (MOR) over carbon-supported platinum (Pt) and platinum-ruthenium (PtRu). On these materials, the MOR involves several well-known intermediates, and it yields products that are amenable to characterization by both SSITKA and auxiliary techniques that can corroborate SSITKA data. Complementary analyses, including in-situ infrared spectroscopy and numerous X-ray and electron-based materials characterization techniques, will be used to inform a holistic examination of the reaction mechanism. New understanding will be generated along several lines of inquiry as captured in two themes. Theme I will focus on experimental kinetics, and will link SSITKA data - obtained across a range of experimental conditions, catalyst particle sizes, and catalyst compositions - to microkinetic models that relate current-voltage characteristics to possible elementary steps. Theme II will utilize a broad range of ex-situ and in-situ characterization methods to identify and control active sites as a function of catalyst composition and synthesis methods. Taken together, the two themes should generate unprecedented insight regarding the factors that control activity and selectivity of catalytic electrochemical methanol oxidation, while also providing a platform for development and refinement of the SSITKA technique. From a technological point of view, the fundamental understanding enabled by the SSITKA technique with respect to kinetics, detailed reaction mechanisms, and catalyst structure-function relationships will be translatable to a broad range of electrochemical reactions. In combination with other techniques, it will provide insight regarding active materials and surface structures that will guide the design of better-performing catalysts. The project will also support graduate and undergraduate education in the area of electrochemistry and renewable energy, as well as several educational and outreach activities already under development by the principal investigator. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.