Electron Beam and In Situ Photon Beam Characterization of PEC Materials and Devices
LaboratorySandia National Laboratories (SNL)
Capability ExpertAlec Talin
Node Readiness Category1: Photoelectrochemical (PEC)
2: Low-Temperature Electrolysis (LTE)
Our key capabilities include electron and photon based methods to map photocarrier excitation/ transport in photoelectrode materials and correlate these characteristics with spatially resolved photoelectrochemical reaction rates measured in situ. Electron bean induced current (EBIC) is performed in a field emission scanning electron microscope (FESEM) retrofitted with two electrical nanomanipulator probes and cathodoluminescence (CL). Using this system we routinely probe nanostructures with dimensions <20 nm and have demonstrated EBIC with <10 nm resolution.1-3 Scanning photocurrent microscopy (SPCM or OBIC) and scanning electrochemical microscopy (SECM) are performed using a modified μRaman microscope with 100 nm step resolution stage and three laser excitation wavelengths (325 nm, 532 nm, and 633 nm). Using this set up we have correlated H2 evolution rates over a metal-insulator-semiconductor PEC cathode with external quantum efficiency (ECE) acquired simultaneously using the SPCM. 4,5 The addition of μRaman (also collected simultaneously) provides local chemical composition of the photoelectrodes and how it evolves over time during operation.
SECM combined with microRaman spectroscopy allows electrochemical activity and composition to be measured with sub-micron spatial resolution.
SNL is an internationally recognized leader in the development of MOFs for practical applications, with several MOF-related "firsts," including integration with MEMS devices, measurement of mechanical properties, catalytic nanoreactors for hydrogen storage, and luminescent MOFs for radiation detection. Our expertise in MOF thin film and membrane fabrication will further the development of high performance and low-cost MEAs.
The capability is available to staff, students and visitors of SNL-CA in Livermore, CA.
In situ measurements of carrier generation/transport, electrochemical reaction rates and electrode composition with high spatial resolution will help explain complex photoelectrochemical H2 evolution mechanisms
(a) A Ge nanowire (~30 nm diam.) is contacted with a nanomanipulator probe (b) EBIC map of a metal/Si nanowire junction (c) Schematic of a cell for simultaneous SPCM and SECM measurements (d,f) SPCM EQE and (e, g) SECM H2 evolution rates mapped for a Pt/SiO2/Si photocathode. The laser source is now coupled to Raman spectrometer for simultaneous vibrational spectroscopic analysis.
Triplett, M. et al. Long Minority Carrier Diffusion Lengths in Bridged Silicon Nanowires. Nano Lett. 15, 523-529, doi:10.1021/nl503870u (2015).
Leite, M. S. et al. Nanoscale Imaging of Photo current and Efficiency in CdTe Solar Cells. ACS Nano 8, 11883-11890, doi:10.1021/nn5052585 (2014).
Leonard, F. & Talin, A. A. Electrical contacts to one- and two-dimensional nanomaterials. Nat. Nanotechnol. 6, 773-783, doi:10.1038/nnano.2011.196 (2011).
Esposito, D. V. et al. Methods of photoelectrode characterization with high spatial and temporal resolution. Energy Environ. Sci. 8, 2863-2885, doi:10.1039/c5ee00835b (2015).
Esposito, D. V., Levin, I., Moffat, T. P. & Talin, A. A. H-2 evolution at Si-based metal-insulator-semiconductor photoelectrodes enhanced by inversion channel charge collection and H spillover. Nat. Mater. 12, 562-568, doi:10.1038/nmat3626 (2013).