In-Situ and Operando Nanoscale Characterization Capabilities for Photoelectrochemical Materials and Integrated Assemblies
LaboratoryLawrence Berkeley National Laboratory (LBNL)
Capability ExpertFrancesca M. Toma
Node Readiness Category1: Low-Temperature Electrolysis (LTE)
2: Photoelectrochemical (PEC)
A combination of different atomic force microscopy (AFM) techniques able to draw structure-function correlations to optimize photoelectrochemical assemblies under operating conditions (e. g. in liquid, under applied bias and illumination).
This suite of characterization techniques comprises peak force AFM (PF-AFM), photoconductive AFM (PC-AFM), kelvin probe force microscopy (KPFM), electrochemical AFM (EC-AFM), and photoelectrochemical AFM (PEC-AFM), for in-situ and operando characterizations of PEC materials and devices. A central aspect of this capability is focused on probing nanoscale properties of photoelectrocatalytic materials under illumination. Nanoscale characterization of photocatalysts in their working environments will enable understanding of reaction mechanisms and pave the way to rational design of efficient and selective heterogeneous photocatalysts of importance in a broad range of applications.
PF-AFM: This technique features direct, precise force control of the AFM measurements, and eliminates damaging lateral forces, thereby enabling high sensitivity and high-resolution current imaging. This is a basic tool that we can employ with all the following capabilities.
PC-AFM: Homogeneity of local conductive properties of photoelectrochemical assemblies can be investigated by PC-AFM, which simultaneously provides very high spatial resolution (~20 nm) for topology and photocurrent. We can offer full control on measurements conditions such as humidity, oxygen level, wavelength and light intensity with sub- and above band gap illumination. We found all these parameters to affect photo-carrier transport and trapping/de-trapping of defect states.
KPFM: Similar to the previous technique we can probe materials heterogeneity by correlating surface potential of photoelectrochemical assemblies with nanoscale morphology. We can control humidity, oxygen level, wavelength and light intensity with sub- and above band gap illumination. Specifically, we can achieve high spatial resolution by utilizing frequency modulated KPFM (FM-KPFM).
EC-AFM: This technique enables the time-lapse topological observation of photoelectrocatalytic and electrocatalytic materials under in situ and operando conditions with very high (<10 nm) spatial resolution.
PEC-AFM: This scanning probe technique will combine scanning electrochemical microscopy (SECM) with photoconductive atomic force microscopy (PC-AFM) for in situ and operando study of heterogeneous photocatalytic reactions at the nanoscale. We can measure contact current and photoelectrochemical current in different environment and under different illumination conditions, and correlate this information to topography. The resolution of this technique is currently <100 nm.
All of these techniques are very versatile. Because of the current geometry of our setup (bottom illumination), samples of interest need to be deposited on transparent and conductive substrates.
In situ and operando characterization of photoelectrochemical systems using light illumination including from various lasers. Control of humidity and oxygen levels for precise measurements. Strong expertise and wide range of techniques.
All of the techniques are utilized in JCAP and other programs but additional projects can be accommodated.
The study of photoelectrochemical assemblies and the understanding of local inhomogeneity and complexity at the nanoscale have the potential to reveal correlations between mescoscale interactions and functionality of materials. The development of advanced in situ and operando characterization techniques provides new opportunities for mechanistic understanding. Insights gained from these measurements on functional materials are expected to enable predictive design and synthesis of functional photocatalytic assemblies with novel properties. These techniques are suitable to directly image local nm-scale PEC activity for in-situ water splitting, and to measure ex-situ the electrical properties in inner material/device to understand the electrical mechanisms behind the PEC performance. The combination of these methods will enable unprecedented access to catalytic mechanisms, dynamic chemical and morphological transformations, and photocorrosion processes at the nano and mesoscale level, thereby providing understanding of the macroscale performance limitations. This information will be instrumental to instruct the synthesis of novel functional photoelectrocatalytic assemblies.
The photograph shows two different modifications of the AFM setup for (a) photoconductive and (b) for electrochemical measurements. (c) Topography image and photocurrent map of the same region of a BiVO4 photoanode measured under illumination (405 nm laser diode) at a bias voltage of 1.75 V. The photoconductive AFM on BiVO4 film shows the photocurrent variation over different grains with nanoscale resolution. (d) PEC-AFM (in dark in this specific case) images showing topography, contact current and electrochemical current. The experiments are performed in 10 mM [Ru(NH3)6]3+ solution as electrolyte. The topography image shows gold squares surrounded by a Si3N4 frame, the height difference is 7 nm.
F. M. Toma, J. K. Cooper, V. Kunzelmann, M. T. McDowell, Jie Yu, D. M. Larson N. J. Borys, C. Abelyan, J. W. Beeman, K. M. Yu, J. Yang, L. Chen, M. R. Shaner, J. Spurgeon, F. A. Houle, K. A. Persson, I. D. Sharp, "Mechanistic Insights into Chemical and Photochemical Transformations of Bismuth Vanadate Photoanodes", Nat. Commun. 2016, 7, article number: 12012. http://dx.doi.org/10.1038/ncomms12012.
S. Y. Leblebici, L. Leppert, Y. Li, S. E. Reyes-Lillo, S. Wickenburg, E. Wong, J. Lee, M. Melli, D. Ziegler, D. K. Angell, D. F. Ogletree, P. D. Ashby, F. M. Toma, J. B. Neaton, I. D. Sharp, A. Weber-Bargioni, "Facet-dependent photovoltaic efficiency variations in single perovskite grains", Nat. Energy 2016, 1, article number: 16093. http://dx.doi.org/10.1038/nenergy.2016.93.