Direct Vibrational Stark Shift Probe of Quasi-Fermi Level Alignment in Metal Nanoparticle Catalyst-Based Metal–Insulator–Semiconductor Junction Photoelectrodes

Photoelectrodes consisting of metal–insulator–semiconductor (MIS) junctions are a promising candidate architecture for water splitting and for the CO₂ reduction reaction (CO₂RR). The photovoltage is an essential indicator of the driving force that a photoelectrode can provide for surface catalytic reactions. However, for MIS photoelectrodes that contain metal nanoparticles, direct photovoltage measurements at the metal sites under operational conditions remain challenging. Herein, we report a new in situ spectroscopic approach to probe the quasi-Fermi level of metal catalyst sites in heterogeneous MIS photoelectrodes via surface-enhanced Raman spectroscopy. Using a CO₂photocathode, nanoporous p-type Si modified with Ag nanoparticles, as a prototype, we demonstrate a selective probe of the photovoltage of ∼0.59 V generated at the Si/SiOₓ/Ag junctions. Because it can directly probe the photovoltage of MIS heterogeneous junctions, this vibrational Stark probing approach paves the way for the thermodynamic evaluation of MIS photoelectrodes with varied architectural designs.

Suo, S.; Sheehan, C.; Zhao, F.; Xiao, L.; Xu, Z.; Meng, J.; Mallouk, T. E.; Lian, T. Direct Vibrational Stark Shift Probe of Quasi-Fermi Level Alignment in Metal Nanoparticle Catalyst-Based Metal–Insulator–Semiconductor Junction Photoelectrodes. J. Am. Chem. Soc., 2023, 145 (26) 14260-14266. https://doi.org/10.1021/jacs.3c02333