Characterizing Degradation Processes at Photoelectrochemically Driven Interfaces
LaboratoryLawrence Livermore National Laboratory (LLNL)
Capability ExpertChris Orme, Trevor Willey
Node Readiness Category1: Photoelectrochemical (PEC)
2: Low-Temperature Electrolysis (LTE)
This capability provides a suite of tools to image and characterize electrochemically or photoelectrochemically driven substrates to monitor their stability during electrolysis. The group has 15+ years of experience characterizing electrochemically driven interface dynamics within a wide range of caustic fluid environments. Tools and expertise include scanning probe based microscopy (SPM), spectroscopy, x-ray scattering and tomography – all in conjunction with measurement of the electrochemical response. Such techniques, particularly in synergistic combinations, enable quantification of corrosion and degradation processes. We have used these methods to characterize semiconductors relevant for PEC cells for industrial partners.
This capability can measure the stability of new candidate materials (such as WSe2 and MoS2) as well as corrosion resistant coatings. X-ray methods and SPM/TEM are complementary techniques that probe physical and electrochemical evolution of the electrode and catalyst. X-ray nano and micro computed tomography (CT) image the internal material morphology during corrosion. X-ray radiography correlates the dissolving interface and adjacent solution concentration & composition with the electrochemical response of the system. For smaller length scales, scanning probe microscopy and surface small & wide X-ray scattering can characterize the change in catalyst morphology, crystalline phase, and electrochemical response in operando. Surface SAXS, TEM and SPM are powerful techniques to characterize the degradation of the catalyst quantitatively by obtaining dissolution and/or agglomeration rates. In cases such as WSe2 or MoS2 resonant SAXS/WAXS can also be employed to focus on the spatial distribution of only one of the components.
Electrode sizes depend upon by technique; generally ranging from 0.01 cm2 up to one cm2 and thicknesses < 0.5 mm in common electrochemical cell configurations. Time resolution is limited by technique (timescales from seconds to several minutes); however, most driven corrosion processes can be significantly slowed by changing the bias potential, enabling the surface to be "quenched" and monitored in a step-wise fashion. X-ray & electron induced chemistry can occur and needs to be considered.
We have extensive and unique capabilities in coupling electrochemical cells into the various scanning probe and x-ray techniques. With our recognized expertise and capabilities, we regularly train visiting scientists on our electrochemical AFM (including the instrument vendor staff). We design, build and use custom electrochemical cells for x-ray spectroscopy, imaging, and scattering capabilities. The group is experienced in developing protocols for quality assured measurements as needed for specific DOE programs. We have written review papers and taught several courses on using SPM to monitor molecular processes at fluid-solid interfaces. Our team includes beamline scientists responsible for implementing electrochemical control into beamline 15-D at the APS and for writing a state-of-the-art tomography analysis package enabling few view reconstruction & in-situ studies.
We have three in situ electrochemical scanning probe microscope stations that include potentiostats, fluid flow and temperature control. Short-term visitors (<2 week) typically work closely with a staff member to ensure quality measurements. Because SPMs are widely available (but typically not operated to their full potential) this capability can serve as a training facility to enable more widespread use in PEC science. Team members have frequent synchrotron beamtime & TEM access via user proposals and approved programs.
This capability can quantify corrosion and degradation processes providing insight into breakdown mechanisms that may guide improvements in both electrode and catalyst materials. Quantification also provides inputs and verification for corrosion modeling.
Table of in operando tools to investigate photoelectrochemically driven interfaces in solution environments
In situ electrochemical SPM/Ellipsometry & Raman: J.P. Bearinger, C.A. Orme, & J.L. Gilbert, Direct observation of hydration of TiO2 on Ti using electrochemical AFM: freely corroding versus potentiostatically held conditions. Surface Science 491, 370-387 (2001); J.J. Gray, B.S. El Dasher, & C.A. Orme, Competitive effects of metal dissolution and passivation modulated by surface structure: An AFM and EBSD study of the corrosion of alloy 22, Surface Science 600, 2488-2494, (2006); J. S. Keist, C.A. Orme, P.K. Wright, & J.W. Evans, An in situ AFM Study of the Evolution of Surface Roughness for Zinc Electrodeposition within an Imidazolium Based Ionic Liquid Electrolyte. Electrochimica Acta, 152, 161–171, doi:10.1016/j.electacta.2014.11.091 (2015).
In-situ Interfacial Electrochemical SAXS: J.A. Hammons et al., Supported Silver Nanoparticle and near-Interface Solution Dynamics in a Deep Eutectic Solvent, The Journal of Physical Chemistry C, (2015.); J.A. Hammons, et al., Interfacial Phenomena During Salt Layer Formation under High Rate Dissolution Conditions, The Journal of Physical Chemistry B, 117, 6724-32, (2013).
In-situ radiography, tomography, and TEM: T.M. Willey, L. Lauderbach, et al.; Journal of Applied Physics, 118 (5) 055901, DOI: 10.1063/1.4927614, (2015). M.H. Nielsen et al., In situ TEM imaging of CaCO3 nucleation reveals coexistence of direct and indirect pathways, Science 345 (6201) 1158-1162, DOI: 10.1126/science.1254051, (2014). M.H. Nielsen et al., Investigating Processes of Nanocrystal Formation and Transformation via Liquid Cell TEM, Microscopy and Microanalysis, 20(2), 425-436, DOI: 10.1017/S1431927614000294, (2014).