In situ/operando Study of Photocatalysis in TEM

Session

PST.6 - In-situ and in-operando microscopy

Authors

Dr. Khim Karki (1), Dr. Pawan Kumar (2), Antoine Verret (2), Noah Glachman (2), Dr. Daan Hein Alsem (1), Prof. Deep Jariwala (2), Norman Salmon (1), Prof. Eric A. Stach (2)

Affiliations

1. Hummingbird Scientific
2. University of Pennsylvania

Keywords

in-situ TEM, optical, photocatalysis, photoelectrochemistry, liquid cell

Abstract text

In-situ/operando liquid cell in transmission electron microscope (TEM) has already provided significant insights into particle dynamics, material synthesis, and electrochemical behavior in great details [1]. In this presentation, we will discuss results from the newly developed in-situ TEM holder that can provide light stimulus in the native liquid environment between the cell, thus enabling photoelectrochemistry in TEM.

 

The introduction of light within the confined liquid environment of TEM strengthens the capability by allowing the study of light interaction in materials during reaction at solid-liquid interface.   The study of hydrogen generation via photoelectrochemical method is one relevant application that can benefit from this technique and can provide fuel for energy storage solution in a clean and environmentally friendly manner [2-4]. Particularly, the atomic scale mechanisms of the photocatalysts that facilitate the water splitting for efficient hydrogen generation are currently poorly understood. The newly developed in-situ/operand optical liquid cell TEM holder [5] capability will enhance in understanding of the role of various photocatalysts and the physics governing the active hydrogen evolution sites for efficient design of photoelectrochemical devices.

 

The studies are performed using liquid cells, which consist of two microfabricated chips sandwiched with transparent SiNx membranes for encapsulating liquid and viewing in the microscope. An optical fiber is routed to the cell allowing direct light exposure to the sample. The optical fiber is coupled externally to the desired light source. The newly developed liquid cell hardware with optical component opens new researches into the photoactive behavior of materials while taking advantage of the exceptional temporal and spatial resolutions of the TEM. 

 

Using the optical liquid cell technique, we study the photo-electrochemical behavior of model materials such as Au nanoprisms and MoS₂ flakes. Au nanoprisms exhibit plasmonically-enhanced catalytic behavior while MoS₂ flakes are known for catalytically active edge sites. In this presentation, we will present the correlation of I-V characteristics with water splitting and simultaneous structural changes at the catalytically active sites, using both model materials. We will also present strategies for site-specific deposition/loading of sample materials in the desired electrodes of liquid cell chips for electroanalytical characterization and TEM imaging. The experimental redox IV characteristic of the sample with light shown enhanced peak compare to the case without light, suggesting light-induced catalytic effect of the sample. The availability and utilization of photo stimuli in liquid cell TEM can provide important fundamental insights into the understanding of several other photoelectrochemical systems [5].   

References

[1] F.M. Ross in Liquid Cell Electron Microscopy, Cambridge University Press (2016)

[2] Nowotny, J.; Sorrell, C. C.; Sheppard, L. R.; Bak, T. Int. J. Hydrogen Energy 2005, 30, 521

[3] Walter, M. G. et al. Solar water splitting cells. Chem. Rev. 110, 6446–6473 (2010)

[4] Maeda, K and Domen, K., J. Phys. Chem. Lett., 1(18), 2655-2661 (2010)

[5] Funding for the development of the sample holder was provided by the Department of Energy,

Office of Basic Energy Sciences, through SBIR Grant # DE-SC0015213