Widely Tunable Ultrafast Photon Source for Interrogation of Hot Electron-driven Electrochemical and Photocatalytic Processes
Abstract
The development of novel strategies to drive electrochemical reactions and photocatalytic processes with improved performance have numerous DoD-relevant applications ranging from portable power to remediation of toxic military byproducts, such as PFAS and electroplating residues. Recently, Prof. CroninÕs lab has demonstrated the effective use of hot-electrons (generated by photoexcitation of plasmon-resonant metal nanostructures and/or high voltage nanosecond transient plasma discharge) to drive several difficult (i.e., high energy barrier) reactions including CO2 reduction to various hydrocarbons, upconversion of methane to higher-order hydrocarbons (e.g., pentane), breakdown of volatile organic compounds (VOCs), and hydrogen evolution. While it is clear that Òhot electronsÓ play an important role in these chemical processes, a fundamental understanding of the energetics and kinetics specifically associated with these hot electrons requires further elucidation. For this purpose, we propose obtaining a femtosecond pulsed laser system capable of outputting an 80 MHz train of pulses with widths of <100 fs across a wavelength range between 226 nm Ð 1040 nm (1.2 eV Ð 5.5 eV) at high average powers up to 2.5 W and peak powers up to 312.5 kW. The output of this laser will be used to first photoexcite a transient burst of hot electrons and then collect spectra with ultrafast time resolution, thus, providing a detailed picture of the hot electron energetics and kinetics. The wide energy range enables spectroscopic studies of various photophysical mechanisms, for example, comparing interband transitions vs. plasmon-resonant excitation and local field enhancement vs. bulk metal absorption processes. Here, the enhanced generation of plasma is localized to the surface of the nanoparticles where it is most useful for catalysis. This pulsed laser source will be integrated with a high voltage (up to 50 kV) nanosecond pulse discharge (USC-patented technology) that can be synchronized with (delayed with respect to) the incident laser pulse. The system will also be coupled to a gated-CCD detector enabling spectra to be collected with < 2 ns time resolution. Together, this system will cover 9 orders of magnitude in time resolution from 1 ps to 1 ms. Once fully integrated with Prof. CroninÕs existing setup, this system will be the first of its kind, enabling tunability over the following parameters: nanosecond pulse voltage and frequency, incident wavelength and intensity, delay times with respect to both the nanosecond voltage pulse and laser pulse, and reference potential, and will directly enhance Prof. CroninÕs hot electron catalysis research currently being carried out under DoD funded grants.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 28, 2022
- Source ID
- W911NF2210084
Entities
People
- Stephen B Cronin
Organizations
- Army Contracting Command
- United States Army
- University of Southern California