The photocatalytic conversion of CO2 to liquid fuels has the dual advantages of carbon recycling for global climate change mitigation and solar energy capture for renewable energy development. However, the obstacles in photocatalytic CO2 reduction are great because the process involves many proton-coupled electron-transfer reactions, posing several fundamental challenges in electrochemistry, photochemistry, and semiconductor physics. This problem presents an opportunity to develop the experimental, theoretical and analytic methods for attacking a complex problem that spans orders of magnitude in length and time scales and requires the complementary modalities of various (x-ray, electron, scanning probe, optical) microscopy and spectroscopy platforms.
The goal of this proposal is to simultaneously (1) develop integrated imaging and visualization approaches across several complementary imaging and spectroscopy platforms in order to (2) advance the understanding of elementary processes involved in CO2 reduction to liquid fuel and spatial and kinetic control of the active sites.
We are focusing on understanding the complex CO2 reduction processes with a multimodal experimental approach. By coupling atomic-scale scanning probes with optical methods, I3 researchers will achieve an atomic-level understanding of how active sites are involved in electron transfer. We will correlate the mobility and longevity of the electronic states during electrochemical reaction or photoactivation. We will do this using atomic- or nanometer-scale dynamic structure probes based on electron or x-ray techniques. We will develop and deliver analytical and experimental tools designed span several platforms.
We plan to primarily use three experimental imaging and spectroscopy platforms:
- Gas-flow SXFM: Scanning X-ray fluorescence spectromicroscopy (SXFM) is well suited to mapping elemental and chemical state distributions of catalytically active materials within flowing gas environments.
- Gas-flow TEM: In situ high-resolution transmission electron microscopy (HRTEM) can probe the relationship between the structure, properties and function of nanostructures and surfaces in a dynamic fashion and under realistic operating conditions. Using the Gatan Imaging Filter system, electron energy loss spectroscopy (EELS) of solid nanomaterials in gaseous environments can be measured to improve the understanding of nanocatalysts’ structure-property-function relationship by exploring electronic structure evolution at the gas-solid interface.
- Laser STM: Scanning tunneling microscopy (STM) and spectroscopy (STS) in an ultrahigh-vacuum (UHV) environment provides atomic-scale information on morphology and electronic structure. Coupled with laser excitation, we plan to investigate photoabsorption, charge separation, and photocatalytic activity on atomic length scales and correlate this behavior with local structure.
A cross-platform gas-flow sample holder will developed to enable correlative measurements on the same catalytic system by SFXM as well as by HRTEM the sample will also be transferrable to UHV for STM studies. The multimodal and multiscale imaging data obtained will present significant challenges to reduce and process on a numerical level and to visualize and interpret at an atomistic level. In order to meet these challenges, we plan to develop novel differential analysis techniques that enable multimodality and integrated imaging studies, and develop first principles atomistic modeling that allows simulation of all of the experimental data from different imaging modalities using the same underlying atomistic model.