We explore various aspects of electrochemistry and photoelectrochemistry using in situ spectroscopy of electrode (metal) and photoelectrode (semiconductor) interfaces under electrochemical working conditions. Using sum frequency generation (SFG) spectroscopy, we measure the voltage dependence of the orientation of D₂O molecules at a graphene electrode surface, which enables us to extract the free energy orienting potential of interfacial water.¹ In particular, we measure the “free OD” feature in the spectra, which corresponds to the topmost water molecule that is rotated up out of the bulk water solution and is, therefore, not hydrogen bonded. Using transient absorption spectroscopy (TAS), we measure the lifetime of hot electrons photoexcited in plasmon resonant nanostructures.⁵ In a similar study, we use transient reflectance spectroscopy (TRS) to measure the photoexcited carrier dynamics in a GaP/TiO₂ photoelectrode, as well as the electrostatic field dynamics at this semiconductor-liquid interface in situ under various electrochemical potentials.² Here, the electrostatic fields at the surface of the semiconductor are measured via Franz−Keldysh oscillations (FKO). These spectra reveal that the nanoscale TiO₂ protection layer enhances the built-in field and charge separation performance of GaP photoelectrodes. Using surface enhanced Raman scattering (SERS) spectroscopy, we monitor local electric fields via Stark-shifts of nitrile-functionalized silicon photoelectrodes.⁶ By monitoring Stark shifts in graphene-enhanced Raman spectroscopy (GERS), we measure local electric fields and local charge densities at monolayer graphene electrode surfaces.³ Lastly, we measure the stacking dependence of monolayer WSe₂/MoSe₂ heterostructures and observe resonant excitation of interlayer excitons for photocatalytic energy conversion.⁴

1. Montenegro, A., C. Dutta, M. Mammetkuliev, H.T. Shi, B.Y. Hou, D. Bhattacharyya, B.F. Zhao, S.B. Cronin and A.V. Benderskii, Asymmetric response of interfacial water to applied electric fields. Nature, 594, 62 (2021).
2. Xu, Z.H., B.Y. Hou, F.Y. Zhao, Z. Cai, H.T. Shi, Y.W. Liu, C.L. Hill, D.G. Musaev, M. Mecklenburg, S.B. Cronin and T.Q. Lian, Nanoscale TiO₂ Protection Layer Enhances the Built-In Field and Charge Separation Performance of GaP Photoelectrodes. Nano Letters, 21, 8017-8024 (2021).
3. Shi, H.T., B.F. Zhao, J. Ma, M.J. Bronson, Z. Cai, J.H. Chen, Y. Wang, M. Cronin, L. Jensen and S.B. Cronin, Measuring Local Electric Fields and Local Charge Densities at Electrode Surfaces Using Graphene-Enhanced Raman Spectroscopy (GERS)-Based Stark-Shifts. ACS Applied Materials & Interfaces, 11, 36252-36258 (2019).
4. Chen, J., C.S. Bailey, D. Cui, Y. Wang, B. Wang, H. Shi, Z. Cai, E. Pop, C. Zhou and S.B. Cronin, Stacking Independence and Resonant Interlayer Excitation of Monolayer WSe₂/MoSe₂ Heterostructures for Photocatalytic Energy Conversion. ACS Applied Nano Materials, DOI:10.1021/acsanm.9b01898 (2020).
5. Yu Wang, Yi Wang, Indu Aravind, Zhi Cai, Lang Shen, Boxin Zhang, Bo Wang, Jihan Chen, Bofan Zhao, Haotian Shi, Jahan M. Dawlaty, and Stephen B. Cronin. In Situ Investigation of Ultrafast Dynamics of Hot Electron-Driven Photocatalysis in Plasmon-Resonant Grating Structures. Journal of the American Chemical Society. DOI: 10.1021/jacs.1c12069 (2022).
6. Haotian Shi, Ryan T. Pekarek, Ran Chen, Boxin Zhang, Yu Wang, Indu Aravind, Zhi Cai, Lasse Jensen, Nathan R. Neale, and Stephen B. Cronin. Monitoring Local Electric Fields using Stark Shifts on Napthyl Nitrile-Functionalized Silicon Photoelectrodes. The Journal of Physical Chemistry C, 124, 17000-17005 (2020).