CAREER: CAS: Colloidal Ligand-Exchange Synthesis of Dilute Noble Metal Surfaces for Electrosynthesis of Hydrogen Peroxide

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With the support of the Chemical Catalysis program in the Division of Chemistry, Professor Christina W. Li of Purdue University is studying catalysts to efficiently prepare hydrogen peroxide directly from air and water using electricity. Hydrogen peroxide is an important commodity chemical that has widespread use in water purification and disinfection. In developing efficient catalysts, this project has the potential to enable small-scale, mobile production for deployment in infrastructure-poor areas. Manufacturing hydrogen peroxide from air and water is a sustainable alternative to the current hydrogen-based process. The catalysts are to be optimized for two key parameters: peroxide productivity (how much hydrogen peroxide is generated for a given amount of electrical energy) and peroxide selectivity (the relative ratio of desired hydrogen peroxide product compared to undesired water by-product). To achieve both high productivity and selectivity, a strategy that enables precise control over the geometric and electronic properties of catalyst nanoparticles (sizes on the order of a few billionths of a meter) will be developed. This approach will use chemistry to prepare catalyst structures ranging in size from single metal atoms to full layers one atom thick with the electronic control provided by the nanoparticle support at the core. Dr. Li's research and educational activities are closely integrated and will educate the next-generation of electrochemistry and battery researchers by engaging students from high school through graduate school. A laboratory activity, the “Battery Design Challenge”, will be developed that is geared toward high school AP Chemistry students in partnership with the AP Fridays program at Purdue University. This activity will bring high school students from across Indiana to Purdue’s campus to compete in this laboratory challenge.With the support of the Chemical Catalysis program in the Division of Chemistry, Professor Christina W. Li of Purdue University will be studying submonolayer core-shell nanoparticles for the electrosynthesis of hydrogen peroxide. Catalysts for peroxide-selective oxygen reduction typically comprise noble metal alloy nanoparticles, in which surface ensemble geometry and electronics are tightly convoluted with the alloy composition. In order to independently control the redox and geometric properties of the catalytic active site, this project will develop a colloidal ligand-exchange deposition strategy to access broadly tunable noble metal surface ensemble geometries—ranging from isolated atoms to small clusters to large islands—in a core-shell nanoparticle. Both metal precursor adsorption and galvanic replacement reactions will be studied to deposit noble metal shells onto a range of core nanoparticle compositions. In both cases, the steric bulk and redox potential of the precursor complex will be tuned though ligand chemistry in order to enforce atom isolation and surface-limited deposition. In addition, operando spectroscopy will be performed to characterize how core-shell and single atom microstructures evolve during electrochemical polarization with the goal of stabilizing the most active and selective surface morphologies. By independently controlling the ensemble geometry and electronic properties of the noble metal surface atoms, this project seeks to develop fundamental structure-mechanism principles for the efficient and selective electrochemical reduction of molecular oxygen to hydrogen peroxide. These systematic and precise materials should permit for the elucidation of optimal ensemble sizes for high selectivity and optimal O-binding strengths for low overpotential peroxide production.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.