In-situ Analytical Tools

Topic #2: In situ analytical tools for (photo)electrochemical materials and devices

bubble-single
In-situ video of a single hydrogen bubble evolving from a catalytic disk on a silicon photoelectrode. Video credit: Anna Dorfi, Jhaelle Payne, and Ellie Prickett.

Key to the successful development of any new catalyst or photocatalyst is the accurate determination of its catalytic activity and the reaction mechanism(s) taking place at its surface. These tasks are especially important for complex, multi-component (photo)catalysts, where deconvoluting the influence of various parameters (true surface area, heterogeneous composition, etc.) can be very difficult. With these challenges in mind, one of the primary thrusts of our research is to develop and employ scanning probe techniques for in-situ evaluation of the optical, electronic, and catalytic properties of (photo)catalytic materials with high spatial resolution. Scanning probe measurement (SPM) techniques can be broadly defined as techniques in which a physical, optical, or electromagnetic probe is scanned across the surface of a sample while the probe/surface interaction is recorded as a function of probe position. Depending on the nature of the probe and its interaction with the surface, the properties of the surface and its surroundings are thus determined with spatial resolution that is generally around the size of the probe tip.

Fig2
a.) Optical image of laser beam and ultramicroelectrode (UME) used to simultaneously perform in-situ SPCM and SECM measurements on a hydrogen-evolving photoelectrode surface. b.) SPCM and c.) SECM maps obtained for photocathode surface in a.). White circles in a.) are the active catalyst deposited on the semiconducting photocathode.

In our lab, the primary in situ SPM techniques to be employed are scanning photocurrent microscopy (SPCM), scanning electrochemical microscopy (SECM), and Raman spectroscopy. In some cases, we employ these techniques in parallel, allowing for simultaneous collection of complementary information that is well-suited for i.) elucidating fundamental nano- and micro-scale charge transfer phenomena  ii.) screening for highly efficient and stable (photo)catalytic materials, iii.) diagnosing inefficiencies observed in macro-scale measurements, and iv.) guiding the design and optimization of cell and materials architectures. Additional efforts in our lab involve the development of novel scanning probe geometries that will enable greatly enhanced areal scan rates and functionality compared to existing SPM probes.

Publications:

  1. D.V. Esposito, J.B. Baxter, J. John, N.S. Lewis, T.P. Moffat, T. Ogitsu, G.D. O’Neil, T.A. Pham, A.A. Talin, J.M. Velazquez, B.C. Wood. “Methods of Photoelectrode Characterization with High Spatial and Temporal Resolution.” Energy & Environmental Science. vol. 8, 2863-2885, 2015.
  2. D.V. Esposito, I. Levin, T.P. Moffat, and A.A. Talin. “Hydrogen Evolution at Si-based Metal-Insulator-Semiconductor Photoelectrodes Enhanced by Inversion Channel Charge Collection and Hydrogen Spillover.” Nature Materials, vol. 12, 562-568 (2013).

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